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STEP 2000

Busway

Table of Contents

Introduction ..............................................................................2 Distribution Systems ................................................................4 Busway Purpose and Definition................................................6 Sentron Busway ..................................................................... 10 Types and Application ............................................................. 11 Design Standards and Ratings................................................ 13 Circuit Protection .................................................................... 18 Busway Construction..............................................................26 Busway System Components ................................................35 Sentron Low Amp Busway .....................................................50 Planning a Sentron Busway System .......................................53 Cable/Conduit Conversion ......................................................70 XL-U Busway...........................................................................73 XJ-L Busway ...........................................................................79 BD Busway .............................................................................82 Trol-E-Duct ..............................................................................86 Review Answers.....................................................................91 Final Exam ..............................................................................92

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Busway and related products. Upon completion of Busway you should be able to:

2

•

Identify the major components of several Siemens busway systems and describe their functions

•

Identify the role of busway in a distribution system

•

Explain the need for circuit protection

•

Identify feeder and plug-in busway and explain the use of each

•

Identify various organizations involved with busway design standards

•

Describe selected sections of the National Electrical Code® (NEC®) as it applies to busway

•

Measure and layout a basic busway system

•

Identify various ratings of Siemens busway

•

Describe how a cost savings is realized when busway is selected over cable and conduit

This knowledge will help you better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. You should complete Basics of Electricity before attempting Busway. An understanding of many of the concepts covered in Basics of Electricity is required for Busway. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. I-T-E, Vacu-Break, Speedfax, and XL-U are registered trademarks of Siemens Energy & Automation, Inc. Sentron, Trol-E-Duct, BD, and XJ-L are trademarks of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code® are reprinted with permission from NFPA 70-2002, National Electrical Code®, Copyright, 2001, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories, Inc. is a registered trademark of Underwriters Laboratories, Inc., Northbrook, IL 60062. The abbreviation “UL” is understood to mean Underwriters Laboratories, Inc. National Electrical Manufacturers Association is located at 2101 L. Street, N.W., Washington, D.C. 20037. The abbreviation “NEMA” is understood to mean National Electrical Manufacturers Association. Other trademarks are the property of their respective owners.

3

Distribution Systems

A distribution system is a system that distributes electrical power throughout a building. Distribution systems are used in every residential, commercial, and industrial building. Distribution systems used in commercial and industrial locations are complex. A distribution system consists of metering devices to measure power consumption, main and branch disconnects, protective devices, switching devices to start and stop power flow, conductors, and transformers. Power may be distributed through various switchboards, transformers, and panelboards. Good distribution systems don’t just happen. Careful engineering is required so that the distribution system safely and efficiently supplies adequate electric service to both present and possible future loads.

4

Distribution Example

In this example of a distribution system the incoming power is 277/480 volts, three-phase, four-wire. The utility company supplies power from a transformer. The secondary winding of the transformer produces 277/480 VAC.

Feeders

A feeder is a set of conductors that originate at a main distribution center and supplies one or more secondary, or one or more branch circuit distribution centers. Three feeders are used in this example. The first feeder is used for various types of power equipment. The second feeder supplies a group of 480 VAC motors. The third feeder is used for 120 volt lighting and receptacles.

5

Busway Purpose and Definition

Commercial and industrial distribution systems use several methods to transport electrical energy. These methods may include heavy conductors run in trays or conduit. Once installed, cable and conduit assemblies are difficult to change. Power may also be distributed using bus bars in an enclosure. This is referred to as busway. Bus Bars

6

A bus bar is a conductor that serves as a common connection for two or more circuits. It is represented schematically by a straight line with a number of connections made to it. Standard bus bars in Siemens busway are made of aluminum or copper.

NEMA Definition

Busway is defined by the National Electrical Manufacturers Association (NEMA) as a prefabricated electrical distribution system consisting of bus bars in a protective enclosure, including straight lengths, fittings, devices, and accessories. Busway includes bus bars, an insulating and/or support material, and a housing.

Busway Used in a Distribution System

A major advantage of busway is the ease in which busway sections are connected together. Electrical power can be supplied to any area of a building by connecting standard lengths of busway. It typically takes fewer man-hours to install or change a busway system than cable and conduit assemblies.

7

The total distribution system frequently consists of a combination of busway and cable and conduit. In this example power from the utility company is metered and enters the plant through a distribution switchboard. The switchboard serves as the main disconnecting means. The feeder on the left feeds a distribution switchboard, which in turn feeds a panelboard and a 480 volt, three-phase, three-wire (3Ø3W) motor. The middle feeder feeds another switchboard, which divides the power into three, three-phase, three-wire circuits. Each circuit feeds a busway run to 480 volt motors. The feeder on the right supplies 120/208 volt power, through a step-down transformer, to lighting and receptacle panelboards. Branch circuits from the lighting and receptacle panelboards supply power for lighting and outlets throughout the plant. In many cases busway can be used in lieu of the cable/conduit feeders at a lower cost.

8

Busway is used in various applications and can be found in industrial installations as well as high-rise buildings. Busway used in industrial locations can supply power to heavy equipment, lighting, and air conditioning. Busway risers (vertical busway) can be installed economically in a high-rise building where it can be used to distribute lighting and air conditioning loads.

9

Sentron Busway

Throughout this course Siemens Sentron™ busway will be used to explain and illustrate principles and requirements of busway. Sentron busway will meet the needs of most busway systems with current ratings from 800 amperes to 5000 amperes. Siemens manufactures several types of busway. There are a number of reasons why different types of busway are manufactured. An existing pre-Sentron busway system, for example, may need to be expanded. Other types of Siemens busway, including significant features, and ratings will be discussed later in the course.

10

Types and Application

Feeder Busway

There are two types of busway, feeder and plug-in. Feeder busway is used to distribute power to loads that are concentrated in one physical area. Industrial applications frequently involve long runs from the power source to a single load. This load may be a large machine, motor control center, panelboard, or switchboard.

Service Entrance

The service entrance is the point of entrance of supply conductors to a building or other structure. Feeder busway, which can be purchased for indoor or outdoor use, can be used as service entrance conductors to bring power from a utility transformer to a main disconnect inside the building.

11

Plug-in Busway

Plug-in busway is used in applications where power requirements are distributed over a large area. Using plug-in units, load connections can be added or relocated easily. Plug-in busway is for indoor use only.

Review 1

12

1.

A ____________ ____________ distributes electrical power throughout a building.

2.

A ____________ is a set of conductors that originate at a main distribution center and supply one or more secondary, or one or more branch circuit distribution centers.

3.

____________ is a type of power distribution device that is made up of heavy bus bars in an enclosure.

4.

It typically takes fewer man-hours to install or change a ____________ system than cable and conduit assemblies.

5.

The two types of busway are ____________ and ______ ______ .

6.

____________ busway can be purchased for use indoors or outdoors, ____________ busway is for indoor use only.

Design Standards and Ratings

Several organizations maintain standards of design, construction, installation, and performance of busway. The following list includes some of these organizations: Underwriters Laboratories, Inc. (UL) The National Electrical Manufacturers Association (NEMA) International Electrotechnical Commission (IEC) The National Electrical Code® (NEC®) Organizations responsible for state and local electrical codes Sentron™ busway meets the worldwide standards of UL 857, IEC 439-1, and IEC 439-2. Underwriters Laboratories

Busway bearing the Underwriters Laboratories listing mark must pass a series of performance tests based on UL publication UL 857. These tests and standards relate to the strength and integrity of a busway system when subjected to specific operating and environmental conditions. UL 1479 provides guidelines for a fire rating. Sentron busway has been tested in accordance with UL 1479 and offers a certified two hour fire rating for gypsum wallboard and a three hour fire rating for concrete slab or cement block. These ratings are achieved by using standard Sentron busway installed with SpecSeal® sealant from Specified Technologies, Inc.

13

NEMA

14

NEMA standards for busway are listed in NEMA publication number BU 1.1-2000. NEMA is primarily associated with equipment used in North America. It is important to note that NEMA short-circuit ratings require a 3 cycle short-circuit rating. This means that the busway was tested and rated on the basis of successfully experiencing 3 cycles of peak current (IP). NEMA recommends the following minimum short-circuit current ratings for busway.

IEC

The International Electrotechnical Commission is associated with equipment sold in many countries, including the United States. IEC standards are found in IEC publications 439 and 529. IEC also recommends short-circuit ratings for busway. Siemens manufacturers Sentron busway with continuous current ratings from 800 amperes to 5000 amperes. The following table shows the short-circuit ratings for Sentron busway. These ratings meet IEC specifications.

15

The following chart lists IEC and UL specifications for enclosure protection of busway.

Feeder or Plug-In Indoor Spray Proof

IP 40 IP 54 & IP55

Feeder Only Outdoor

16

NEMA 3R

National Electrical Code®

The National Electrical Code® (sponsored by the National Fire Protection Association), once adopted by the authority having jurisdiction, stipulates installation requirements which are necessary for the safe application of electrical equipment. ® Article 368 of the NEC® specifically applies to busway, ® although other articles in the NEC® are applicable in certain ® situations. Thorough familiarization of the NEC® requirements for busway is recommended. 368.1 368.2 368.4 368.5 368.6 368.7 368.8 368.9 368.10 368.11 368.12 368.13 368.15

State and Local Codes

Scope Definition Use Support Through Walls and Floors Dead Ends Branches from Busways Overcurrent Protection Rating of Overcurrent Protection - Feeders Reduction in Ampacity Size of Busway Feeder of Branch Circuits Rating of Overcurrent Protection - Branch Circuits Marking

State and local authorities have electrical codes which are often more stringent than other organizations. You are encouraged to become familiar with this material in your local area. In addition, busway is frequently used for the main electrical service of a building, in which case the busway is connected to one or more distribution transformers owned by local electric power companies. Electrical power companies throughout the United States prefer different methods of connecting to busway. It is recommended that the local power company be contacted before applying or installing a service entrance busway run.

NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association.

17

Circuit Protection

Circuit protection must be taken into consideration with any electrical circuit, including busway. Current flow in a conductor always generates a watts loss in the form of heat. As current flow increases, the conductor must be sized appropriately in order to compensate for higher watt losses. Excess heat is damaging to electrical components. For that reason, conductors have a rated continuous current carrying capacity or ampacity. Overcurrent protection devices are used to protect conductors from excessive current flow. Two devices used to protect circuits from overcurrent are fuses and circuit breakers. These protective devices are designed to limit the flow of current in a circuit to a safe level, preventing the circuit conductors from overheating.

The National Electrical Code® defines overcurrent as any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault (Article 100-definitions).

NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association. Reprinted with permission from NFPA 70-2002, the National Electrical Code®, Copyright© 2001, National Fire Protection Association, Quincy, MA 02269.

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Circuit protection would be unnecessary if overloads and short circuits could be eliminated. Unfortunately, overloads and short circuits do occur. To protect a circuit against these currents, a protective device must determine when a fault condition develops and automatically disconnect the electrical equipment from the voltage source. Inverse Time-Current Characteristic

An overcurrent protection device must be able to recognize the difference between overcurrents and short circuits and respond in the proper way. Protection devices use an inverse time-current characteristic. Slight overcurrents can be allowed to continue for some period of time, but as the current magnitude increases, the protection device must open faster. Short circuits must be interrupted instantly.

Fuse Construction

A fuse is the simplest device for interrupting a circuit experiencing an overload or a short circuit. A typical fuse, like the one shown below, consists of an element electrically connected to end blades or ferrules. The element provides a current path through the fuse. The element is enclosed in a tube and surrounded by a filler material.

19

Overcurrent

Current flowing through the element generates heat, which is absorbed by the filler material. When an overcurrent occurs temperature in the element rises. In the event of a harmless transient overload condition the excess heat is absorbed by the filler material. If a sustained overload occurs the heat will eventually melt open an element segment forming a gap; thus stopping the flow of current.

Short-Circuit Current

Short-circuit current can be several thousand amperes and generates extreme heat. When a short circuit occurs several element segments can melt simultaneously, which helps remove the load from the source voltage quickly. Short-circuit current is typically cut off in less than half a cycle, before it can reach its full value.

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Nontime-Delay Fuses

Nontime-delay fuses provide excellent short circuit protection. Short-term overloads, such as motor starting current, may cause nuisance openings of nontime-delay fuses. They are best used in circuits not subject to large transient surge currents. Nontime-delay fuses usually hold 500% of their rating for approximately one-fourth second, after which the current carrying element melts. This means that these fuses should not be used in motor circuits which often have inrush (starting) currents greater than 500%.

Time-Delay Fuses

Time-delay fuses provide overload and short circuit protection. Time-delay fuses usually allow five times the rated current for up to ten seconds. This is normally sufficient time to allow a motor to start without nuisance opening of the fuse unless an overload persists.

Ampere Rating

Fuses have a specific ampere rating, which is the continuous current carrying capability of a fuse. The ampere rating of a fuse, in general, should not exceed the current carrying capacity of the circuit. For example, if a conductor is rated for 10 amperes, the largest fuse that would be selected is 10 amperes. There are some specific circumstances when the ampere rating is permitted to be greater than the current carrying capacity of the circuit. For example, motor and welder circuits can exceed conductor ampacity to allow for inrush currents and duty cycles within limits established by the NEC®.

Sentron Fusible Switches

Plug-in fusible switches are available on Siemens busway. Sentron™ fusible switches, for example, are rated from 30 - 600 amperes.

Voltage Rating

The voltage rating of a fuse must be at least equal to the circuit voltage. The voltage rating of a fuse can be higher than the circuit voltage, but never lower. A 600 volt fuse, for example, can be used in a 480 volt circuit. A 250 volt fuse could not be used in a 480 volt circuit.

Ampere Interrupting Capacity (AIC)

Fuses are also rated according to the level of fault current they can interrupt. This is referred to as ampere interrupting capacity (AIC). When applying a fuse, one must be selected which can sustain the largest potential short circuit current which can occur in the selected application. The fuse could rupture, causing extensive damage, if the fault current exceeds the fuse interrupting rating.


21

UL Fuse Classification

22

Fuses are grouped into current limiting and non-current limiting classes based on their operating and construction characteristics. Fuses that incorporate features or dimensions for the rejection of another fuse of the same ampere rating but with a lower interruption rating are considered current limiting fuses. Underwriters Laboratories (UL) establishes and standardizes basic performance and physical specifications to develop its safety test procedures. These standards have resulted in distinct classes of low voltage fuses rated at 600 volts or less. The following chart lists various UL fuse classes.

Circuit Breakers

Another device used for overcurrent protection is a circuit breaker. The National Electrical Code® defines a circuit breaker as a device designed to open and close a circuit by nonautomatic means, and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating (Article 100 - definitions). Circuit breakers provide a manual means of energizing and deenergizing a circuit. In addition, circuit breakers provide automatic overcurrent protection of a circuit. A circuit breaker allows a circuit to be reactivated quickly after a short circuit or overload is cleared. Unlike fuses which must be replaced when they open, a simple flip of the breaker’s handle restores the circuit.

Ampere Rating

Like fuses, every circuit breaker has a specific ampere, voltage, and fault current interruption rating. The ampere rating is the maximum continuous current a circuit breaker can carry without exceeding its rating. As a general rule, the circuit breaker ampere rating should match the conductor ampere rating. For example, if the conductor is rated for 20 amperes, the circuit breaker should be rated for 20 amperes. Siemens I-T-E® breakers are rated on the basis of using 60° C or 75° C conductors. This means that even if a conductor with a higher temperature rating were used, the ampacity of the conductor must be figured on its 60° C or 75° C rating. NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association. Reprinted with permission from NFPA 70-2002, the National Electrical Code®, Copyright© 2001, National Fire Protection Association, Quincy, MA 02269.

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There are some specific circumstances when the ampere rating is permitted to be greater than the current carrying capacity of the circuit. For example, motor and welder circuits can exceed conductor ampacity to allow for inrush currents and duty cycles within limits established by NEC®. Generally the ampere rating of a circuit breaker is selected at 125% of the continuous load current. This usually corresponds to the conductor ampacity which is also selected at 125% of continuous load current. For example, a 125 ampere circuit breaker would be selected for a load of 100 amperes. Sentron MCCB Plug-In Units

Plug-in devices with molded case circuit breakers (MCCB) are available on Sentron busway with circuit breaker ratings from 125 - 800 amperes.

Voltage Rating

The voltage rating of the circuit breaker must be at least equal to the circuit voltage. The voltage rating of a circuit breaker can be higher than the circuit voltage, but never lower. For example, a 480 VAC circuit breaker could be used on a 240 VAC circuit. A 240 VAC circuit breaker could not be used on a 480 VAC circuit. The voltage rating is a function of the circuit breakers ability to suppress the internal arc that occurs when the circuit breaker’s contacts open.

Fault Current Interrupting Rating

Circuit breakers are also rated according to the level of fault current they can interrupt. When applying a circuit breaker, one must be selected which can sustain the largest potential short circuit current which can occur in the selected application. Siemens circuit breakers have interrupting ratings from 10,000 to 200,000 amperes. To find the interrupting rating of a specific circuit breaker refer to the Speedfax® catalog.

Additional Information

For additional information on circuit breakers refer to the STEP 2000 course, Molded Case Circuit Breakers.

24

Review 2 1.

In accordance with UL 1479, Sentron busway offers a ____________ hour fire rating for gypsum wallboard, and a ____________ hour fire rating for concrete slab when used with SpecSeal® sealant.

2.

Sentron busway, with a continuous current rating of 800 amperes and aluminum bus bars, has a 60 cycle shortcircuit rating of ____________ amperes.

3.

The highest level of enclosure protection of Sentron feeder busway is IP ____________ and the highest level of enclosure protection of Sentron plug-in busway is IP ____________ .

4.

Article ____________ in the National Electrical Code® specifically applies to busway.

5.

A Class R has an ampere interrupting capacity of ______ ______ amperes.

6.

Siemens circuit breakers have a fault current interrupting capacity of ____________ to ____________ amperes.


25

Busway Construction

Bus Bars

A better understanding of what busway is can be gained by examining its construction. A typical Siemens Sentron™ busway section has three or four formed aluminum or copper bars that function as electrical conductors. Aluminum busway can be supplied in ampacities up to 4000 amperes. Copper busway can be supplied in ampacities up to 5000 amperes.

Bus bars manufactured for use in feeder busway differ from those manufactured for use in plug-in busway. Plug-in busway will have a tab or some other form of connecting a plug-in device such as a disconnect.

26

Each bus bar is referred to as a phase. Bus bars of Sentron busway are separated electrically with epoxy insulation.

Enclosure

Glass wrap tape is wrapped around the Sentron bus bars to provide additionally protection and hold the bars together. The bus bars are then installed in an enclosure. The enclosure provides protection and support.

27

Bars per Pole

Sentron busway uses one bar per pole on busway rated up to 2000 amperes aluminum and 2500 amperes copper.

Sentron busway uses two bars per pole on busway rated from 2500 to 4000 amperes aluminum and 3000 to 5000 amperes copper.

28

NEMA Phase Arrangement

Bus bars are required to have phases in sequence so that an installer can have the same fixed phase arrangement in each termination point. This is established by NEMA (National Electrical Manufacturers Association). The following diagram illustrates accepted NEMA phase arrangements.

The following illustration shows the proper phase arrangement of bus bars in Sentron busway.

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Number of Bus Bars

The number of bars depends on the number of phases on the power supply and whether or not a neutral or ground is used.

200% Neutral

Siemens Sentron busway is available with a 200% neutral within the bus bar housing. Certain loads on the distribution system can cause non-sinusodial current referred to as harmonics. These harmonics cause circulating currents which increase the heat in the system and shorten component life. The 200% neutral capacity minimizes overheating, thus prolonging the life of power distribution equipment.

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Ground

The National Electrical Code® requires the metal enclosure of any busway run to be grounded back at the service entrance equipment. Sentron busway has several options to meet this requirement. The busway housing is an integral ground. Under more severe industrial applications a heavier ground may be required. The following cross section drawing of Sentron busway shows a bus bar a 50% internal ground has been added. This means that the ground is rated at 50% of the ampacity of the phase bus bars.

Busway Lengths

The standard length of a plug-in busway section is 10’ (3048 mm). Sentron busway is also available in 4’ (1219 mm), 6’ (1829 mm), and 8’ (2438 mm) lengths.

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Plug-in outlets on Sentron plug-in busway are located on 2’ (610 mm) centers on both sides of the busway.

Sentron Plug-In Outlets

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The Sentron plug-in outlet features a molded guard which prevents incidental finger contact with live conductors. This meets IEC, IP 2X requirements for preventing a 0.472” (12 mm) probe from entering. This is referred to as finger safe.

Feeder Busway Lengths

In addition to the 4’ (1219 mm), 6’ (1829 mm), 8’ (2438 mm), and standard 10’ (3048 mm) lengths, Sentron feeder busway sections are available in 0.125” (3.2 mm) increments from 1’ 4.5” (419 mm) to 10’ (3048 mm). Feeder busway does not have any plug-in outlets.

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Review 3

34

1.

In the Sentron busway, aluminum bus bars are available with ampacities up to ____________ amperes and copper bus bars are available with ampacities up to ____________ amperes.

2.

Identify the type of busway each of the bus bars represent in the following illustration.

3.

Plug-in busway is available in ____________ , ____________ , ____________ , and 10 foot lengths.

4.

Plug-in outlets are located on ____________ foot centers.

5.

Sentron feeder busway sections are available in ____________ inch increments from ____________ to ____________ feet.

Busway System Components

There are a number of components that make up a busway system. The various system components illustrated in this section, unless otherwise noted, will be the Siemens Sentron™ series. For more information on any component consult the Sentron Busway System Selection and Application Guide. It should also be noted that certain components available on one type busway system may not be available on another type busway system. Although components used in various busway systems perform the same or similar functions, they can’t be interchanged from one busway system to another. There are a number of reasons for this. Systems are tested and rated as a complete unit. Ratings and system integrity could not be guaranteed when components are interchanged between systems. Additionally, components from one system may not physically fit or connect to components of another system. Sections of Siemens Sentron busway, for example are clamped together with a joint stack. Siemens BD™ busway is bolted together.

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Joint Stack

The Siemens Sentron busway system, uses a single-bolt joint stack to connect busway sections. The bus bars from two busway sections are slid into a joint stack.

The assembly is clamped solidly together with the single bolt located on the joint stack. Sentron busway sections and components are supplied with required joint stacks.

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The single-joint bolt is a double-headed break-off bolt. The outer head is 5/8” and the bottom head is 3/4” . The doubleheaded bolt is tightened until the 5/8” outer head twists off (approximately 55 ft. lbs.). This eliminates the need for torque wrenches during initial installation. The bottom 3/4” head is permanent and is used for future joint maintenance. Each joint is adjustable by ± 5/8” .

Elbows

Elbows, offsets, and tees allow for turns and height changes in the busway system to made in any direction. An elbow can turn the busway system right or left, up or down. Elbows are supplied with a joint stack and covers.

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Combination Elbows

Combination elbows can turn the busway system up or down, and right or left.

Tees

Tees are used to start a new section of busway in a different direction. Tees can start a new section to the right, to the left, up, or down. Tees are supplied with two joint stacks.

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Crosses

A cross allows a busway run to expand in four directions.

Offsets

Offsets allow the busway system to continue in the same direction. Offsets can move the busway system to the right, to the left, up, or down. Offsets are supplied with a joint stack.

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Cable Tap Boxes

Tap boxes are used to connect electrical cable to the busway distribution system. End cable tap boxes can be installed at either end of the busway system. They can be used on feeder or plug-in busway.

Center, or plug-in, cable tap boxes can be installed along the length of a busway system. Plug-in cable tap boxes can only be used on plug-in busway.

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Stubs

Sentron busway standard stubs can be used to connect busway to other Siemens equipment, such as switchgear and switchboards. Sentron busway stubs can be shipped installed in Siemens switchboards and switchgear. This eliminates the field labor required to connect the busway to the switchboard, saving the installer time and money.

Flanged Ends

Flanged ends are also used to connect busway equipment such as switchgear and switchboards. These can be used with existing equipment. Siemens will furnish the outline drawings of this flanged end to the coordinating switchboard or equipment installer.

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Service Heads

Service heads are used to connect the busway to the electric service. There are two types in the Sentron series. A single service head that has all three phases, or three separate heads, one for each phase.

Riser Adaptors

In busway, a riser is a length of vertical busway. Panelboards and meter centers can be mounted directly to risers with a side-mounted adapter. When Sentron plug-in busway is used as a riser, plug-in receptacles are located only on one side.

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Phase Rotation

Some applications may require a phase rotation of the power supply to be reversed. The direction of rotation of a 3Ø AC motor, for example, is determined by the phase sequence of the power supply.

Reducers

A busway reducer is used to reduce the allowable ampere rating. Money can often be saved by using a lower rated group of sections near the end of a busway run. A branch circuit, for example, does not need as high an ampere rating as the main feeder circuit. Article 368.11 of the NEC® states that overcurrent protection shall be required where busways are reduced in ampacity. There is an exception to this article. Exception: For industrial establishments only, omission of overcurrent protection shall be permitted at points where busways are reduced in ampacity, provided that the length of the busway having the smaller ampacity does not exceed 15 m (50 ft) and has an ampacity at least equal to one-third the rating or setting of the overcurrent device next back on the line, and provided further that such busway is free from contact with combustible material. NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association. Reprinted with permission from NFPA 70-2002, the National Electrical Code®, Copyright© 2001, National Fire Protection Association, Quincy, MA 02269.

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Sentron busway offers fused reducers to meet the requirement of NEC® Article 368.11, and non-fused reducers when the exception is allowed. Illustrated below is a fused reducer.

Expansion Fittings

Expansion fittings are used when a busway system crosses an expansion joint in a building, or on long straight runs where both ends are held in a permanent fixed position. The Sentron expansion fitting contains a sliding expansion enclosure. Flexible connectors in the expansion enclosure allow a ±2” movement.


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Bus Plugs

Sentron II busway bus plugs are available with Siemens Sentron molded case circuit breakers or Siemens fusible switch.

Sentron II bus plugs feature a visible position indicator and relocateable operating handle. Alignment and interlock tabs prevent the plug from being installed 180° out of position and ensures that the plug is in the off position during installation and removal. Clamp assemblies are used to draw the bus plug firmly against the busway housing. Sentron Bus Plugs are designed with standard wire bending space and extended wire bending space (gutter). Plug-in units can be mounted horizontally or vertically (riser).

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In-line Disconnect Cubicle

Cubicles provide a means of mounting switches or circuit breakers where power enters or leaves a busway system. Inline disconnect cubicles are used where bolted connections are preferred, or at ampere ratings exceeding the standard plug-in unit ratings.

End Closer

End closers are used to safely terminate a run of busway and protect the bus bar ends.

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Hangers

Various hangers are used to support busway. When a vertical run of busway passes through a floor, a floor support is required. Spring hangers provide secure mounting of Sentron busway in riser applications. These hangers counter the weight of the busway on each floor and compensate for minimal building movement and thermal expansion.

Several types of hangers are available to suspend the busway from the ceiling, structural steel support, or mounted to a wall.

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Flanges

Wall, ceiling, and floor flanges are designed to close off the area around the busway as it passes through a wall, ceiling, or floor. The flange does not provide an air tight seal around the busway.

Roof flanges provide a watertight seal when outdoor rated busway enters through a roof. The pitch or angle of the roof must be specified when ordering roof flanges.

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Review 4 Identify the components in the following illustration:

1.

____________

2.

____________

3.

____________

4.

____________

5.

____________

6.

____________

7.

____________

8.

____________

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Sentron Low Amp Busway

Sentron Low Amp Busway is a member of the Siemens Sentron Busway family. Sentron Low Amp Busway specifically addresses the needs of low amp power distribution applications, with ratings from 225A to 800A UL and 100A to 800A IEC. Low Amp Busway provides all the features and advantages of Sentron Busway.

Plug-In Sections

Sentron Low Amp is available as plug-in only, with aluminum or copper bus bars. Aluminum bars are available in 225 - 600 ampere sections. Copper bars are available in 225 - 800 ampere sections. Sections include an integral housing ground. An optional copper internal or isolated ground is available in most ratings. Sentron Low Amp plug-in sections are available in 4’ (1219 mm), 6’, (1829 mm) 8’ (2438 mm), and 10’ (3048 mm) sections. Plugin openings are centered on 24” (610 mm) and staggered on both sides of the busway. Plug-in outlets, like standard Sentron, are finger safe and IP 2X rated. Plug-in sections are protected to IP40 specifications. IP54 is optionally available.

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Bus Plugs

Sentron II bus plugs used with standard Sentron can also be used with Sentron Low Amp.

Joint Stack Assembly

Sentron Low Amp uses the same joint stack assembly design as standard Sentron.

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Hangers

In addition to the hanger shown below, Sentron Low Amp is available with the same type hangers and supports as available with standard Sentron.

Components

Sentron Low Amp is available with a full range of elbows, tees, offsets, tap boxes, flanged ends, expansion fittings, reducers, and phase rotation fittings.

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Planning a Sentron Busway System

There are several considerations when planning a busway run. The best route would require the fewest fittings and the maximum number of 10’ straight sections. There are a number of techniques to ensure an accurate measurement before purchasing and installing busway. The following procedures are given as an example and are useful in obtaining a correct measurement. Laser Measuring Device

Laser measuring devices, such as the one illustrated below, provide an easy and highly accurate means of measuring a busway run.

Note: Consult Busway factory for laser measuring device information.

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Laser measuring devices project a laser beam which is reflected on an object such as a wall, ceiling, floor, or piece of machinery. The measuring device is able to accurately measure the distance the beam travels.

When measuring the distance from wall-to-wall or wall-toobstruction, place the laser measuring device flat against the wall. The distance measured will be from the wall to the point the laser beam is interrupted.

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Laying Out a Run

Using the laser measuring device, determine the height and location of obstructions. Select a route requiring the fewest offsets.

The planned route can be laid out on the floor with a pencil or chalk. Transfer the position of pipes, ducts, beams, and other obstructions to the floor. It will be easier to transfer the planned busway route to paper if significant portions are laid out full scale first.

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Once the route is laid out the laser measuring device can be used along the run to measure distance.

Walls, Ceilings, Floors

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When piercing a wall, ceiling, or floor find a reference point which is common to both sides and measure from it. This may be a pipe, a wall, or a door.

Sample Layout

In the following example, a busway system, connected to a switchboard, will pass through three rooms. The floor to ceiling height is 15’ on the first floor, and 12’6” on the second floor. The overall length is 42’. Walls and floors are 6” thick. The switchboard is a standard 90” high. Various types of equipment on the second floor will be connected to the busway through plug-in outlets along the length of the room.

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It is determined that a clear space is available 13’ above the floor in the switchboard room (5’6” from the top of the switchboard). The clear space extends on the other side of the wall in the second room to the far right wall. It is also clear on the second floor along the far right wall and 10’ above the floor for the length of the second floor.

A rough sketch can now be made of the proposed busway system route.

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NEC® Requirements

An important part of applying a busway system is to be sure that the system meets the requirements of The National Electrical Code®.

Article 368.4

According to NEC® Article 368.4, busways shall be permitted to be installed where they are located as follows: (1)

Located in the open and are visible, except as permitted in 368.6 or

(2)

Installed behind access panels, provided the busways are totally enclosed, of nonventilating-type construction, and installed so that the joints between sections and at fittings are accessible for maintenance purposes. Where installed behind access panels, means of access shall be provided, and the following conditions shall be met: a. The space behind the access panels shall not be used for air-handling purposes; or b. Where the space behind the access panels is used for environmental air, other than ducts and plenums, in which case there shall be no provisions for plug-in connections, and the conductors shall be insulated.


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Article 368.4 also restricts the use of busway in conditions where it may be damaged or cause damage. Busways shall not be installed as follows: (1) Where subject to severe physical damage or corrosive vapors (2) In hoistways (3) In any hazardous (classified) location, unless specifically approved for such use (4) Outdoors or in wet or damp locations unless identified for such use. Lighting busway and trolley busway shall not be installed less than 2.5 m (8 ft) above the floor or working platform unless provided with a cover identified for the purpose. Article 364.5

Article 368.5 requires adequate support for the busway. The following drawing illustrates one type of support available for Siemens Sentron™ busway. Busways shall be securely supported at intervals not exceeding 1.5 m (5 ft) unless otherwise designed and marked. Note: Picture frame and trapeze hangers used with Sentron Busway are designed on a maximum of 3.05 m (10 ft) centers.


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Article 368.6

Article 368.6 allows busway to pass through walls and floors provided there are no section joints in the wall or floor and vertical busway extends at least 6 feet through the floor. In addition, certain applications a curb may be required around busway passing through two or more dry floors. This will help eliminate the possibility of spilled liquid from running down the busway causing damage to the electrical system. (A) Walls. Unbroken lengths of busway shall be permitted to be extended through dry walls. (B) Floors. Floor penetrations shall comply with (1) and (2): (1) Busways shall be permitted to be extended vertically through dry floors if totally enclosed (unventilated) where passing through and for a minimum distance of 1.8 m (6 ft) above the floor to provide adequate protection from physical damage. (2) In other than industrial establishments, where a vertical riser penetrates two or more dry floors, a minimum 100 mm (4 in.) high curb shall be installed around all floor openings for riser busways to prevent liquids from entering the opening. The curb shall be installed within 300 mm (12 in.) of the floor opening. Electrical Equipment shall be located so that it will not be damaged by liquids that are retained by the curb. In addition to NEC® requirements, Sentron busway requires a minimum of 7” from a wall to a joint where a new section of busway begins. Sentron busway passing through a floor requires a minimum of 16” between the floor and a joint. This space is required for the floor supports.

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Article 368.7

Article 368.7 states that a dead end of a busway shall be closed. The following drawing illustrates the end closer used on Sentron busway.

Minimum Clearance

There are certain minimum clearances required when installing busway near a wall, ceiling, or another busway run. It is beyond the scope of this course to cover in detail the minimum clearances of every component. The minimum clearances of Sentron busway components are listed in the Sentron™ Busway Systems Selection and Application Guide. Specifications for other systems are listed in their respective selection and application guides.

Dimensions

Component dimensions must also be considered when planning a busway system. The dimensions given in the following examples are for illustrative purposes. For a complete listing of Sentron busway components refer to the Sentron™ Busway Systems Selection and Application Guide. Specifications for other systems are listed in their respective selection and application guides.

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Section Dimensions

It has already been mentioned that Sentron plug-in busway is available in 4’, 6’, 8’, and 10’ sections, and feeder busway is available in lengths from 2’ to 10’ in increments of 0.125”. The height of Sentron busway is 5” . The width varies with the maximum amperage rating. The width of 800 amp, one-bar-perpole aluminum Sentron busway, for example, is 4.5” wide.

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Other Component Dimensions

Other components, such as elbows, offsets, and tees must also be considered. Right and left elbows, for example, vary from 12” x 12” to 24” x 24” . This is due to the variance of bus bar width with amperage rating. An 800 ampere aluminum system, for example, would be 12” x 12”. Up or down elbows are 10” x 10” .

In the example busway system, the busway will be connected to a switchboard. A flanged end must also be selected. The flanged end is 8” long from the flange to the joint stack.

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System Assembly

The components can now be selected for the installation. A switchboard flanged end (8”(203 mm)), a 4’ (1219 mm) length of feeder busway, and one elbow (10” (254 mm)) is selected. The total height is 5’6” (1676 mm).

The busway runs horizontally on the first floor 31’8” (9652 mm) before making its second turn. Feeder busway is selected because no equipment will be connected to it on the first floor. A second elbow and three 10’ (3048 mm) feeder sections are selected.

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It is 2’6” (762 mm) from the top of the horizontal feeder run to the second floor level. The horizontal busway run on the second floor will be installed 10’ (3048 mm) from the floor, for a total rise of 12’6” (3810 mm). One elbow is already installed on the first floor horizontal feeder busway run. A second elbow will be needed at the top of the vertical riser. Each elbow is 10” (254 mm), which is subtracted from the total rise of 12’6” (3810 mm). 10’10” (3302 mm) of vertical riser will complete the vertical rise.

In addition to the standard lengths of 4’ (1219 mm), 6’ (1829 mm), 8’ (2438 mm), and 10’ (3048 mm), Sentron feeder busway also comes in any length from 2’ (609 mm) to 10’ (3048 mm) in 0.125” (3.17 mm) increments. One solution for the vertical riser might be to select one 6’ (1829 mm) and one 4’10” (1473 mm) section.

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The busway run is completed with three 10’ (3048 mm) plug-in sections on the second floor.

An end closer, wall and floor flanges, floor support, hangers, and the desired number of plug-in units finish the system. In this example three plug-in units were used.

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Bill of Material

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We now have the dimensions needed to assemble a bill of material for our example project.

Information Needed to Order Busway

The following information is necessary when planning a busway installation or expansion:

•

Description of application

•

Type of busway

•

Voltage and number of conductors

•

Maximum current

•

Length and configuration of run

•

Location and type of power supply to busway

•

Number of hangers

•

Type and number of tap-off devices (tees, crosses)

•

Type and number of accessories

Review 5 1.

According to NEC® Article 368.7 a dead end of a busway shall be ____________ .

2.

Dimensions of Sentron busway can be found in the _____________________________________________ .

3.

A right elbow with copper bus bars, rated at 5000 amperes has an X measurement of ____________ inches and a Y measurement of ____________ inches.

4.

According to NEC® Article 368.5 busway shall be securely supported at intervals not exceeding ____________ feet unless the busway is otherwise designed and marked.

5.

According to the National Electrical Code® it ____________ to extend unbroken lengths of busway through dry walls. a. is permissible b. is not permissible


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Cable/Conduit Conversion

Busway can be used in many applications where cable and conduit are more commonly used. The question arises, “Why use busway instead of conventional cable and conduit?”

Benefits of Busway

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There are several reasons why busway may be a better choice over cable and conduit. Busway provides greater flexibility by allowing equipment to be connected anywhere along the run on 24” centers. Equipment can be easily disconnected and moved to a new location without major rewiring.

Busway has a smaller cross section. This means less installation space is required. Sentron™ busway with aluminum bus bars rated at 1000 amperes, for example, occupies a much smaller space than a comparable cable and conduit installation. The smaller cross section also means that busway is lighter in weight, by as much as half, which means less loading on the building.

The installed cost of busway is typically less than cable and conduit. Busway is easier to install. Sections are simply hung and joined together using readily available hardware. Total installed costs associated with using Sentron busway over cable and conduit typically results in 20 - 30% lower installed cost.

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Sentron Busway Estimating Program

A software program, available from Siemens, compares the total installed price of cable and conduit to Sentron busway.

Comparison Example

The following table shows one example of the cost savings of busway over cable and conduit. The job calls for a 500 foot run of 1350 amperes. A hypothetical labor rate of $37.15 an hour is used. It will take an estimated 455 hours to install the cable and conduit. It will take an estimated 134 hours to install Sentron busway. The total savings, by using Sentron busway, is $12,693.

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XL-U Busway

XL-U® is available in both feeder and plug-in busway with ratings of 225 to 5000 amperes with aluminum bus bars or 225 to 6500 amperes with copper bus bars. Maximum voltage is 600 volts. XL-U feeder busway is available in either indoor or outdoor ventilated types. XL-U plug-in busway is indoor only and ventilated. XL-U is available in 3Ø3W and 3Ø4W.

Paired Phases

XL-U is available with a paired-phase bus bar scheme. Bus bars are grouped in pairs so that AC current in each pair is nearly equal in magnitude and opposite in direction. Two bus bars per phase are used. Phase C is paired with phase A, phase A is paired with phase B, and phase B is paired with phase C. The result is a minimized magnetic field. Current is balanced and temperature rise is kept to a minimum. Voltage drop is reduced. XL-U busway can be used on any application within its current rating but it is usually used for long runs where end-of-run voltage is critical. Due to its paired-phase design, XL-U busway is known throughout the industry as the best product available for welder loads.

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Sections and Components

XL-U feeder busway sections can be supplied in any length from 14” (356 mm) to 10’ (3048 mm). XL-U Plug-in busway is available in 4’ (1269 mm), 6’ (1828 mm), 8’ (2438 mm), and 10’ (3048 mm) sections. Elbows, tees, crosses, end closers, wall flanges, tap boxes, flanged end connections, switchboard connections, bus plugs, reducers, and hangers are available.

Joint Stack

XL-U busway uses a joint stack, similar to the Sentron™ busway, to connect sections together. The joint stack bolt is secured with a recommended 35 ft. lbs. of torque.

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One Bar Per Phase

XL-U busway is available from 225 to 6500 amperes. The number of bus bars and the dimensions depends on the maximum current rating. XL-U busway can be mounted vertically or horizontally, either edgewise or flatwise. The cross sections illustrated below are shown edgewise mounted. The “W” dimension varies with the current rating. There are two maximum current ratings for XL-U, UL and standard rating. XL-U busway is available in a one-bar-per-phase configuration for the maximum current ratings shown in the following table.

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Two Bars Per Phase

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XL-U busway is available in a two-bar-per-phase, paired- phase configuration for the maximum current ratings shown in the following table.

Four Bars Per Phase

At higher current ratings bus bars are doubled up. Four bars per phase are used in the current ratings shown in the following table. Note that paired-phasing is still used.

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Eight Bars Per Phase

To accommodate even higher current levels eight bars per phase are used.

Components

The following components are available for XL-U busway:

• • • • • • • • • •

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Hangers End closers Flanged ends Plug-in and center cable tap boxes Elbows Offsets Tees Crosses Reducers and expansion sections Bus plugs (circuit breaker, fusible)

XJ-L Busway

When an application needs a horizontal run of plug-in busway with a current rating that does not exceed 200 amperes, Siemens XJ-L™ would be a good choice. XJ-L busway is available with 100 or 200 ampere capacities, three-phase, three-wire (3Ø3W), 600 VAC or three-phase, four-wire (3Ø4W), 600 VAC. The neutral bus bar in the 3Ø4W type is rated for 100%. XJ-L busway is available in 2’ (610 mm), 5’ (1524 mm), and 10’ (3048 mm) lengths. There are up to 12 plug-ins per 10’ (3048 mm) length. Plug-ins are located in alternate positions from side-to-side.

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Installation

All XJ-L busway sections mate together end-to-end with overlapping joints which are held in place by integral spring pressure clips.

The sections are bolted together with captive screws.

Components

The following components are available for XJ-L busway:

• • • • • • •

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Hangers End closers Flanged ends Plug-in and center cable tap boxes Elbows Tees Bus plugs (circuit breaker, fusible)

XQ-R bus plug

XQ-R bus plugs serve both 120 and 240 VAC needs. This is useful for computer applications, laboratory/test facilities, schools, hospitals, and machine shops.

Review 6 1.

The installed cost of busway is typically ____________ than cable and conduit. a. b.

more less

2.

The maximum current rating available with XL-U busway with aluminum bus bars is ____________ amperes.

3.

____________ ____________ is a unique feature of XL-U busway that results in a magnetic field cancellation.

4.

To accommodate levels of current in the 3000 to 5000 ampere range, using aluminum XL-U busway, _________ ___ bars per phase are used.

5.

XJ-L is available in either ____________ ampere or ____________ ampere capacities.

6.

The ____________ is a bus plug available for XJ-L busway which provides 120 and 240 VAC.

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BD Busway

The BD™ busway is a general purpose power distribution busway of the plug-in design. BD busway is well established in the industry and has proven to be a dependable system. BD busway was first introduced in 1932, and with the exception of minor upgrades in materials, the basic design has remained unchanged. This means older systems can be expanded with today’s BD busway components.

Installation

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The bus bars of one end of a section are offset and the other end is straight. To connect two sections together match an offset end with a straight end. When ordering new BD busway to expand an existing system it is important to note if the new connection will be to an existing offset or straight end.

Bus bars are bolted together with a recommended 25 ft. lbs. of torque.

Plug-Ins

Each 10’ (3048 mm) section has ten bus plug receptacles, spaced alternately on each side (five on each side) of the busway section. Circuit breaker plugs are available in sizes from 100 to 800 amperes for voltages of 600 VAC or less. Fusible ® Vacu-Break switch plugs are available in sizes of 30 to 600 amperes, 3-pole, 600 VAC or less, or 4-pole solid neutral, 240 or 480 VAC. Capacitor and transformer bus plugs are also available. Capacitor bus plugs are used to reduce inductive heating and improving power factor. Transformer bus plugs furnish singlephase 120 or 240 VAC for lighting, small motors, or portable tools. Transformer plugs are also available with or without twopole AC magnetic contactors for plugging in on three-phase 240 or 480 VAC.

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Ratings and Dimensions

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BD busway comes in 10’ (3048 mm) lengths in current ratings from 225 to 1600 amperes. The number of bus bars per phase is determined by the current rating. A section of 225 amperes aluminum busway, for example, would have one bar per phase. A section of 1000 ampere aluminum busway would have two bus bars per phase. The following busway cross section diagram and table reflect ampere ratings and dimensions of BD busway.

Components

The following components are available for BD busway:

• • • • • • • •

Hangers End closers Flanged ends Plug-in and center cable tap boxes Elbows Tees Crosses Bus plugs (circuit breaker, fusible)

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Trol-E-Duct

Trol-E-Duct™ is part of the Siemens busway family. This busway is designed to provide power to indoor moving equipment, such as cranes, conveyors, hoists, mobile tools, and similar moving equipment.

Ratings

Trol-E-Duct is available in the following ratings: Indoor 1Ø2W, 1Ø3W, 3Ø3W, 3Ø4W 100 to 800 amperes 600 VAC

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Construction

Bus bars inside a housing provide power to a trolley. Brushes, mounted on the trolley, make contact with the bus bars. The trolley can be moved along an internal channel that is part of the housing. A section of the bus bar can be removed and replaced with a spacer that can be as small as ¼” (6.35 mm) or as large as 1’ (305 mm). It may be desirable to have a system that is powered only at specific locations. In these cases less expensive busless casings can be used throughout the unpowered sections.

Sections

Trol-E-Duct sections can be straight or curved. Curved sections are available only for 100 ampere busway. Curved sections can either be horizontal (shown) or vertical (not shown). Curved sections join with straight sections to create a continuous Trol-E-Duct system that matches any structural pattern. Curved sections are available for any radius of two feet or greater.

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Trolleys

Several types of trolleys are available for Trol-E-Duct. There are two types of tool hanger trolleys. Types TPTH and TBTH. Both types of tool hangers should not be used on a curved section with a radius of less than 5’. Type TPTH has provision for wiring a tool to the trolley. Type TBTH also has space for starters, receptacles and fuses.

Several other types of trolleys are available for a wide variety of applications. In the following example a hoist is wired to a trolley. The hoist moves along a monorail that runs parallel to a Trol-E-Duct system.

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Standard Trolleys

Standard trolleys are recommended for applications where the load current is less than 30 amperes, trolley speed is less than 5 m.p.h., and the curve radius is 5’ (1524 mm) or larger.

Heavy-Duty Trolleys

Heavy duty trolleys are used where the load current is less than 60 amperes, trolley speed is less than 5 m.p.h., and the curve radius is 5’ (1524 mm) or larger. By adding an additional pigtail between the brush and the wire grip the trolley can be rated as high as 90 amperes.

Roller-Type Trolleys

Roller-type trolleys are used on lighter duty applications. The load current is less than 20 amperes and the trolley speed does not exceed 2.5 m.p.h. Roller-type trolleys will negotiate a 5’ (1524 mm) radius curve.

Curved-Type Trolleys

Curved-type trolleys will negotiate a curve with a 3’ (914 mm) radius or greater, speeds up to 5 m.p.h., and loads as high as 60 amperes.

Button-Type Trolleys

Button-type trolleys will negotiate a curve with a 5’ (1524 mm) radius or greater, speeds up to 5 m.p.h., and loads as high as 60 amperes. Extra wheels on this trolley make it well suited for carrying a heavy weight.

Transfer Trolley

The transfer trolley is rated at 30 amperes and is suited for applications where the trolley must jump a gap in duct. Flared ends are used on the bus duct when the trolley must jump. The trolley can jump a separation as great as 3/8” (9.5 mm) with sections misaligned as much as 3/8” (9.5 mm). It will negotiate a curve with a radius of 2’ (610 mm) or greater.

Nylon Brush Trolley

Nylon brush trolleys have brushes which are used to remove abrasive material, such as metallic or cement dust, from the bus bars.

Abrasive Trolley

Abrasive trolleys are designed to clean and remove corrosive buildup from bus bars in harsh atmospheres.

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Review 7

90

1.

BD busway was first introduced in ____________ .

2.

When ordering new BD busway to expand an existing system it is important to note if the new connection will be to an existing ____________ or straight end.

3.

Fusible Vacu-Break switches are available in sizes of ____________ to ____________ amperes for BD busway.

4.

____________ is a type of busway that is designed to provide power to moving equipment such as cranes or hoists.

5.

Standard Trol-E-Duct trolleys can handle a curve radius of ____________ feet or larger.

Review Answers

Review 1

1) distribution system; 2) feeder; 3) Busway; 4) busway: 5) feeder, plug-in; 6) Feeder, plug-in.

Review 2

1) two, three; 2) 47,000; 3) 66, 54; 4) 368; 5) 200,000; 6) 10,000, 200,000.

Review 3

1) 4,000, 5,000; 2) a. feeder, b. plug-in; 3) 4’, 6’, 8’; 4) 2; 5) 0.125, 1’ 4.5” , 10’.

Review 4

1) C; 2) F; 3) A; 4) B; 5) E; 6) H; 7) G; 8) D.

Review 5

1) closed; 2) Sentron Busway Systems Selection and Application Guide; 3) 24, 24; 4) 5; 5) a.

Review 6

1) b; 2) 5000; 3) Paired phases; 4) eight; 5) 100, 200; 6) XQ-R.

Review 7

1) 1932; 2) offset; 3) 30, 600; 4) Trol-E-Duct; 5) 5.

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Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. Questions

1.

The two types of busway are ____________ . a. b. c. d.

2.

It typically takes ____________ man-hours to install a busway system than cable and conduit. a. b.

3.

fewer twice as many

10,000 14,000

c. d.

22,000 42,000

2X 40

c. d.

43 54

General guidelines which discuss the safe application of busway are covered in the NEC® Article ____________ . a. b.

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c. d.

According to IEC 529, a plug-in outlet that is said to be “finger safe” has an IEC code of IP ____________ . a. b.

5.

about the same more

According to NEMA publication number BU 1.1-2000, the short-circuit rating of plug-in busway with a maximum continuous current rating of 1000 amperes should be at least ____________ amperes. a. b.

4.

feeder and service entrance feeder and plug-in plug-in and service entrance indoor and outdoor

368 445

c. d.

365 450

6.

The interrupting rating of a class R fuse is ____________ amperes. a. b.

7.

50,000 200,000

2,000 3,000

c. d.

4,000 5,000

The following Sentron bus bar is used for ____________ busway.

a. b. 9.

c. d.

The maximum current rating of Sentron™ busway with aluminum bus bars is ____________ amperes. a. b.

8.

10,000 100,000

feeder plug-in

c. d.

service entrance outdoor

Plug-in outlets on Sentron busway are located on ____________ centers. a. b.

16” (406 mm) 2’ (610 mm)

c. d.

30” (762 mm) 3’ (914 mm)

10. A Sentron busway expansion fitting allows for an expansion compensation of ± ____________ . a. b.

2” (50.8 mm) 1’ (305 mm)

c. d.

18” (457 mm) 6” (152 mm)

11. ___________ are used to house Siemens molded case circuit breakers or fusible switches. a. b.

Reducers Service heads

c. d.

Bus Plugs Expansion fittings

12. ____________ are used to safely terminate a run of busway and protect the bus bar ends. a. b.

End closers Service heads

c. d.

Tees Flanged ends 93

13. A minimum distance of ____________ from the wall to a joint where the new section of busway begins is required when Sentron busway passes through a wall. a. b.

4” (102 mm) 7” (127 mm)

c. d.

6” (152 mm) 10” (254 mm)

14. The dimensions of a Sentron right elbow, with aluminum bus bars, rated for 1000 amperes is ____________ . a. b.

10” x 10” 12” x 12”

c. d.

18” x 18” 24” x 24”

15. The paired-phase bus bar scheme is used with ____________ busway. a. b.

Sentron XJ-L

c. d.

XL-U BD

16. The maximum current rating of XL-U busway with copper bus bars is ____________ amperes. a. b. 17.

3000 4000

c. d.

5000 6500

The maximum current rating of XJ-L busway is ____________ amperes. a. b.

100 5000

c. d.

200 6000

18. The type of Siemens busway that was first introduced in 1932 is ____________ busway. a. b.

Sentron XJ-L

c. d.

XL-U BD

19. ____________ is the type of Trol-E-Duct tool box hanger that provides space for starters, receptacles and fuses. a. b.

TBTH TPTH

c. d.

Transfer trolley Button-type trolley

20. Curved Trol-E-Duct sections are available for ____________ . a. b. c. d. 94

any radius of 2’ (610 mm) or greater a 2’ (610 mm) radius only any radius of 5’ (1524 mm) or greater a 5’ radius only (1524 mm)

quickSTEP Online Courses

quickSTEP online courses are available at http://www.sea.siemens.com/step. The quickSTEP training site is divided into three sections: Courses, Downloads, and a Glossary. Online courses include reviews, a final exam, the ability to print a certificate of completion, and the opportunity to register in the Sales & Distributor training database to maintain a record of your accomplishments. From this site the complete text of all STEP 2000 courses can be downloaded in PDF format. These files contain the most recent changes and updates to the STEP 2000 courses. A unique feature of the quickSTEP site is our pictorial glossary. The pictorial glossary can be accessed from anywhere within a quickSTEP course. This enables the student to look up an unfamiliar word without leaving the current work area.

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Table of Contents

Introduction ............................................................................. 2 Control Circuits........................................................................ 4 Electrical Symbols ................................................................... 6 Line Diagrams ....................................................................... 16 Overload Protection............................................................... 22 Overload Relays .................................................................... 26 Manual Control ...................................................................... 35 Magnetic Contactors and Starters ......................................... 41 Starter Ratings ....................................................................... 46 Furnas INNOVA PLUS Starters .............................................. 49 ESP100 Starters .................................................................... 50 SIRIUS Type 3R Starters ........................................................ 51 World Series Type 3TF Starters .............................................. 53 Multi-Speed and Reversing Starters ...................................... 55 Reduced-Voltage Starting ...................................................... 59 Solid-State Reduced-Voltage Controllers ............................... 64 Pilot Devices ......................................................................... 67 Control Transformers .............................................................. 78 Control Relays ....................................................................... 79 Timing Relays ........................................................................ 85 Pressure Switches ................................................................ 90 LOGO! Logic Module ............................................................ 93 Review Answers ................................................................... 96 Final Exam ............................................................................. 97

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Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Basics of Control Components and related products. Upon completion of Basics of Control Components you will be able to:

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State the purpose and general principles of control components and circuits

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State the difference between manual and automatic control operation

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Identify various symbols which represent control components

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Read a basic line diagram

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Describe the construction and operating principles of manual starters

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Describe the construction and operating principles of magnetic contactors and magnetic motor starters

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Identify various Siemens and Furnas manual starters and magnetic motor starters, and describe their operation in a control circuit

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Explain the need for motor overload protection

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State the need for reduced-voltage motor starting

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Describe typical motor starting methods

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Describe the difference between normally open and normally pilot devices

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Describe the operating principles of control relays

This knowledge will help you better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. You should complete Basics of Electricity before attempting Basics of Control Components. An understanding of many of the concepts covered in Basics of Electricity is required for Basics of Control Components. In addition, you may want to complete the STEP 2000 course Sensors after completing Basics of Control Components. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. Siemens & Furnas Controls is a business unit of Siemens Energy & Automation, Inc. SIMICONT is a registered trademark of Siemens Energy & Automation, Inc. INNOVA PLUS and ESP100 are trademarks of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-1999, National Electrical Code Copyright, 1998, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories Inc. is a registered trademark of Underwriters Laboratories Inc., Northbrook, IL 60062. The abbreviation “UL” shall be understood to mean Underwriters Laboratories Inc. CAGE CLAMP is a trademark of WAGO Corporation, Brown Deer, WI 53223

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Control Circuits

The National Electrical Code® (NEC®) defines a controller as a device or group of devices that serves to govern, in some predetermined manner, the electrical power delivered to the apparatus to which it is connected (Article 100-definitions). Control

Control, as applied to control circuits, is a broad term that means anything from a simple toggle switch to a complex system of components which may include relays, contactors, timers, switches, and indicating lights. Every electrical circuit for light or power has control elements. One example of a simple control circuit is a light switch used to turn lights on and off.

Of course there are many other devices and equipment systems in industrial applications. Motor control, for example, can be used to start and stop a motor and protect the motor, associated machinery, and personnel. In addition, motor controllers might also be used for reversing, changing speed, jogging, sequencing, and pilot-light indication. Control circuits can be complex: accomplishing high degrees of automatic and precise machine operation.

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Manual Control

Control is considered to be manually operated when someone must initiate an action for the circuit to operate. For example, someone might have to flip the switch of a manual starter to start and stop a motor.

Automatic Operation

While manual operation of machines is still common practice, many machines are started and stopped automatically. Frequently there is a combination of manual and automatic control. A process may have to be started manually, but may be stopped automatically.

Control Elements

The elements of a control circuit include all of the equipment and devices concerned with the circuit function. This includes enclosures, conductors, relays, contactors, pilot devices, and overcurrent-protection devices. The selection of control equipment for a specific application requires a thorough understanding of controller operating characteristics and wiring layout. The proper control devices must be selected and integrated into the overall plan.

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Electrical Symbols

Language has been developed in order to transfer ideas and information. In order to understand the ideas and information being communicated, an understanding of the language is necessary. The language of controls consists of a commonly used set of symbols which represents control components. Contact Symbols

Contact symbols are used to indicate an open or closed path of current flow. Contacts are shown as normally open (NO) or normally closed (NC). Contacts shown by this symbol require another device to actuate them.

The standard method of showing a contact is by indicating the circuit condition it produces when the actuating device is in the deenergized or nonoperated state. For example, in the following illustration a relay is used as the actuating device. The contacts are shown as normally open, meaning the contacts are open when the relay is deenergized. A complete path of current does not exist and the light is off.

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Normally Open Contact Example

In a control diagram or schematic, symbols are usually not shown in the energized or operated state. For the purposes of explanation in this text, a contact or device shown in a state opposite of its normal state will be highlighted. For example, in the following illustration the circuit is first shown in the deenergized state. The contacts are shown in their normally open (NO) state. When the relay is energized, the contacts close completing the path of current and illuminating the light. The contacts have been highlighted to indicate they are now closed. This is not a legitimate symbol. It is used here for illustrative purposes only.

Normally Closed Contact Example

In the following illustration the contacts are shown as normally closed (NC), meaning the contacts are closed when the relay is deenergized. A complete path of current exists and the light is on. When the relay is energized, the contacts open turning the light off.

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Switch Symbols

Switch symbols are also used to indicate an open or closed path of current flow. Variations of this symbol are used to represent limit switches, foot switches, pressure switches, level switches, temperature-actuated switches, flow switches, and selector switches. Switches, like contacts, require another device or action to change their state. In the case of a manual switch someone must manually change the position of the switch.

Normally Open Switch Example

In the following illustration a battery is connected to one side of a normally open switch and a light to the other. Current is prevented from flowing to the light when the switch is open. When someone closes the switch, the path of current flow is completed and the light illuminates.

Normally Closed Switch Example

In the following illustration a battery is connected to one side of a normally closed switch and a light to the other. Current is flowing to the light when the switch is closed. When someone opens the switch, the path of current flow is interrupted and the light turns off.

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Pushbutton Symbols

There are two basic types of pushbuttons: momentary and maintained. A normally open momentary pushbutton closes as long as the button is held down. A normally closed momentary pushbutton opens as long as the button is held down. A maintained pushbutton latches in place when the button is pressed.

Normally Open Pushbutton Example

In the following illustration a battery is connected to one side of a normally open pushbutton and a light is connected to the other side. When the pushbutton is depressed, a complete path of current flow exists through the pushbutton and the light is illuminated.

Normally Closed Pushbutton Example

In the following example current will flow to the light as long as the pushbutton is not depressed. When the pushbutton is depressed, current flow is interrupted and the light turns off.

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Coil Symbols

Coils are used in electromagnetic starters, contactors, and relays. The purpose of contactors and relays is to open and close associated contacts. A letter is used to designate the coil; for example, “M” frequently indicates a motor starter and “CR” indicates a control relay. The associated contacts have the same identifying letter. Contactors and relays use an electromagnetic action which will be described later to open and close these contacts. The associated contacts can be either normally open or normally closed.

Coil Example Using Normally Open Contacts

In the following example, the “M” contacts in series with the motor are controlled by the “M” contactor coil. When someone closes the switch, a complete path of current flow exists through the switch and “M” contactor coil. The “M” contactor coil actuates the “M” contacts which provide power to the motor.

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Overload Relay Symbols

Overload relays are used to protect motors from overheating due to an overload on the driven machinery, low-line voltage, or an open phase in a three-phase system. When excessive current is drawn for a predetermined amount of time, the relay opens and the motor is disconnected from its source of power.

Pilot Light Symbols

A pilot light is a small electric light used to indicate a specific condition of a circuit. For example, a red light might be used to indicate a motor is running. The letter in the center of the pilot light symbol indicates the color of the light.

Other Symbols

In addition to the symbols discussed here, there are many other symbols used in control circuits. The following chart shows many of the commonly used symbols.

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Abbreviations

Abbreviations are frequently used in control circuits. The following list identifies a few commonly used abbreviations. AC ALM AM ARM AU BAT BR CAP CB CKT CONT CR CT D DC DISC DP DPDT DPST DT F FREQ FTS FU GEN GRD HOA IC INTLK IOL JB LS LT M

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Alternating Current Alarm Ammeter Armature Automatic Battery Brake Relay Capacitor Circuit Breaker Circuit Control Control Relay Current Transformer Down Direct Current Disconnect Switch Double-Pole Double-Pole, Double-Throw Double-Pole, Single-Throw DoubleThrow Forward Frequency Foot Switch Fuse Generator Ground Hand/Off/Auto Selector Switch Integrated Circuit Interlock Instanstaneous Overload Junction Box Limit Switch Lamp Motor Starter

MTR MN NEG NEUT NC NO OHM OL PB PH POS PRI PS R REC RES RH S SEC SOL SP SPDT SPST SS SSW T TB TD THS TR U UV VFD XFR

Motor Manual Negative Neutral Normally Closed Normally Open Ohmmeter Overload Pushbutton Phase Positive Primary Pressure Switch Reverse Rectifier Resistor Rheostat Switch Secondary Solenoid Single-Pole Single-Pole, Double Throw Single-Pole, Single Throw Selector Switch Safety Switch Transformer Terminal Board Time Delay Thermostat Switch Time Delay Relay Up Under Voltage Variable Frequency Drive Transformer

Review 1 1.

A control is ____________ operated when someone must initiate an action for the circuit to operate.

2.

Which of the following symbols represents a normally open contact?

a. 3.

b.

c.

Which of the following symbols indicates a normally open pushbutton? a.

5.

c.

Which of the following symbols represents a normally closed contact?

a. 4.

b.

b.

c.

Which of the following symbols indicates a mushroom head pushbutton? a.

b.

c.

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Line Diagrams

The method of expressing the language of control symbols is a line diagram, also referred to as a ladder diagram. Line diagrams are made up of two circuits, the control circuit and the power circuit. Electrical wires in a line diagram are represented by lines. Control-circuit wiring is represented by a lighter-weight line and power-circuit wiring is represented by a heavier-weight line. A small dot or node at the intersection of two or more wires indicates an electrical connection.

Line diagrams show the functional relationship of components and devices in an electrical circuit, not the physical relationship. For example, the following illustration shows the physical relationship of a pilot light and a pushbutton.

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The functional relationship can be shown pictorially with the following illustration.

Reading a Line Diagram

This functional relationship is shown symbolically with a line diagram. Line diagrams are read from left to right. Depressing the pushbutton would allow current to flow from L1 through the pushbutton, illuminating the pilot light, to L2. Releasing the pushbutton stops current flow turning the pilot light off.

Power Circuit and Control Circuit

The power circuit, indicated by the heavier-weight line, is what actually distributes power from the source to the connected load (motor). The control circuit, indicated by the lighter-weight line, is used to “control” the distribution of power.

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Connecting Loads and Control Devices

Control circuits are made up of control loads and control devices. The control load is an electrical device that uses electrical power. Pilot lights, relays, and contactors are examples of control loads. Control devices are used to activate the control load. Pushbuttons and switches are examples of control devices. The following illustration shows the proper connection of a pilot light (load) with a pushbutton (control device). The power lines are drawn vertically and marked L1 and L2. In this example the voltage potential between L1 and L2 is 120 VAC. The pilot light selected must be rated for 120 VAC. When the pushbutton is depressed, the full 120 volt potential is applied to the pilot light.

Connecting the Load to L2

Only one control load should be placed in any one circuit line between L1 and L2. One side of the control load is connected to L2 either directly or, in some instances, through overload relay contacts. In the following example a pilot light is directly connected to L2 on one circuit line. A contactor coil is indirectly connected through a set of overload contacts (OL) to L2 on a second circuit line. This is a parallel connection. Depressing the pushbutton would apply 120 VAC to the pilot light and the “M” contactor.

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Control loads are generally not connected in series. The following illustration shows two ways to connect a control load. In one instance the control loads are improperly connected in series. When the pushbutton is depressed, the voltage across L1 and L2 is divided across both loads, the result being that neither load will receive the full 120 volts necessary for proper operation. If one load fails in this configuration, the entire circuit is rendered useless. In the other instance the loads are properly connected in parallel. In this circuit there is only one load for each line between L1 and L2. The full 120 volts will appear across each load when the pushbutton is depressed. If one load fails in this configuration, the other load will continue to operate normally.

Connecting Control Devices

Control devices are connected between L1 and the load. The control device can be connected in series or parallel, depending on the desired results. In the following illustration, the pushbuttons are connected in parallel. Depressing either pushbutton will allow current to flow from L1, through the depressed pushbutton, through the pilot light, to L2.

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In the following illustration, two pushbuttons are connected in series. Both pushbuttons must be depressed in order to allow current to flow from L1 through the load to L2.

Line Numbering

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Numbering each line makes it easier to understand more complex line diagrams. In the following illustration, line 1 connects pushbutton 1 to pilot light 1. Line 2 connects pushbutton 2 to pilot light 1. Line 3 connects switch 1 to pilot light 2 and the “M” contactor on line 4.

Review 2 1.

Line diagrams are read from ____________ to ____________ , or L1 to L2.

2.

Match the items on the line diagram with the associated list.

A ____________ B ____________ C ____________ D ____________ E ____________ F ____________

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Overload Protection

Before discussing specific control components, it is necessary to review what an overload is and what steps can be taken to limit the damage an overload can cause. Current and Temperature

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Current flow in a conductor always generates heat due to resistance. The greater the current flow, the hotter the conductor. Excess heat is damaging to electrical components. For that reason, conductors have a rated continuous current carrying capacity or ampacity. Overcurrent protection devices are used to protect conductors from excessive current flow. Thermal overload relays are designed to protect the conductors (windings) in a motor. These protective devices are designed to keep the flow of current in a circuit at a safe level to prevent the circuit conductors from overheating.

Excessive current is referred to as overcurrent. The National Electrical Code® defines overcurrent as any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault (Article 100-definitions). Short Circuits

When two bare conductors touch, a short circuit occurs. When a short circuit occurs, resistance drops to almost zero. Shortcircuit current can be thousands of times higher than normal operating current.

Ohm’s Law demonstrates the relationship of current, voltage, and resistance. For example, a 240 volt motor with 24 ohms of resistance would normally draw 10 amps of current.

When a short circuit develops, resistance drops. If resistance drops to 24 milliohms, current will be 10,000 amps.

The heat generated by this current will cause extensive damage to connected equipment and conductors. This dangerous current must be interrupted immediately when a short circuit occurs.

Reprinted with permission from NFPA 70-1999, the National Electrical Code®, Copyright© 1998, National Fire Protection Association, Quincy, MA 02269.

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Overload Conditions

An overload occurs when too many devices are operated on a single circuit or a piece of electrical equipment is made to work harder than it is designed for. For example, a motor rated for 10 amperes may draw 20, 30, or more amperes in an overload condition. In the following illustration a package has become jammed on a conveyor causing the motor to work harder and draw more current. Because the motor is drawing more current it heats up. Damage will occur to the motor in a short time if the problem is not corrected or the circuit is not shut down by the overload relay.

Temporary Overload Due to Starting Current

Electric motors are rated according to the amount of current they will draw at full load. When most motors start, they draw current in excess of the motor’s full-load current rating. Motors are designed to tolerate this overload current for a short period of time. Many motors require 6 times (600%) the full-load current rating to start. Some newer, high-efficiency motors may require higher starting currents. As the motor accelerates to operating speed, the current drops off quickly. The time it takes for a motor to accelerate to operating speed depends on the operating characteristics of the motor and the driven load. A motor, for example, might require 600% of full-load current and take 8 seconds to reach operating speed.

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Overload Protection

Fuses and circuit breakers are protective devices used to protect circuits against short circuits, ground faults, and overloads. In the event of a short circuit, a properly sized fuse or circuit breaker will immediately open the circuit. There is, however, a dilemma that occurs when applying fuses and circuit breakers in motor control circuits. The protective device must be capable of allowing the motor to exceed its fullload rating for a short time. Otherwise, the motor will trip each time it is started. In this situation it is possible for a motor to encounter an overload condition which does not draw enough current to open the fuse or trip the circuit breaker. This overload condition could easily cause enough heat to damage the motor. In the next section we will see how overload relays are used to solve this problem.

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Overload Relays

Overload relays are designed to meet the special protective needs of motor control circuits. Overload relays:

Trip Class

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allow harmless temporary overloads, such as motor starting, without disrupting the circuit

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will trip and open a circuit if current is high enough to cause motor damage over a period of time

•

can be reset once the overload is removed

Overload relays are rated by a trip class, which defines the length of time it will take for the relay to trip in an overload condition. The most common trip classes are Class 10, Class 20 and Class 30. Class 10, for example, has to trip the motor off line in 10 seconds or less at 600% of the full load amps. This is usually sufficient time for the motor to reach full speed. Many industrial loads, particularly high inertia loads, use Class 30. Siemens standard overload relays are Class 10 or Class 20 with Class 30 available with some starters.

Overload Relay in a Motor Circuit

The following illustration shows a motor circuit with a manual starter and overloads. Current flows through the overloads while the motor is running. Excess current will cause the overload to trip at a predetermined level, opening the circuit between the power source and the motor. After a predetermined amount of time the starter can be reset. When the cause of the overload has been identified and corrected the motor can be restarted.

Bimetal Overloads

Overload protection is accomplished with the use of a bimetal strip. This component consists of a small heater element wired in series with the motor and a bimetal strip that can be used as a trip lever. A bimetal strip is made of two dissimilar metals bonded together. The two metals have different thermal expansion characteristics, so the bimetal bends at a given rate when heated. Under normal operating conditions the heat generated by the heater element will be insufficient to cause the bimetal strip to bend enough to trip the overload relay.

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As current rises, heat also rises. The hotter the bimetal becomes, the more it bends. In an overload condition the heat generated from the heater will cause the bimetal strip to bend until the mechanism is tripped, stopping the motor.

Some overload relays that are equipped with a bimetal strip are designed to automatically reset the circuit when the bimetal strip has cooled and reshaped itself, restarting the motor. If the cause of the overload still exists, the motor will trip again and reset at given intervals. Care must be exercised in the selection of this type of overload as repeated cycling will eventually damage the motor.

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Ambient Compensated Overload Relay

In certain applications, such as a submersible pump, the motor may be installed in a location having a constant ambient temperature. The motor control, along with the overload relay, may be installed in a location with a varying ambient temperature. The trip point of the overload relay will vary with the temperature of the surrounding air as well as current flowing through the motor. This can lead to premature and nuisance tripping. Ambient compensated overload relays are designed to overcome this problem. A compensated bimetal strip is used along with a primary bimetal strip. As the ambient temperature changes, both bimetal strips will bend equally and the overload relay will not trip the motor. However, current flow through the motor and the heater element will affect the primary bimetal strip. In the event of an overload condition the primary bimetal strip will engage the trip unit.

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Class 48 Bimetal Ambient Compensated Overload Relay

The Class 48 bimetal ambient compensated overload relay is available in single-pole or three-pole designs. Unlike the melting alloy overload relay, the bimetal ambient compensated overload relay can be set for manual or self-resetting operation. An adjustment dial located on the unit allows the ampere trip setting to be adjusted by ±15%. The bimetal ambient compensated overload relay heater elements are available in Class 20 or Class 10 ratings. A normally open or normally closed auxiliary contact is available as an option.

SIRIUS 3RU11 Overload Relay

The Siemens SIRIUS 3RU11 is a bimetal type of overload relay with the heater elements as an integral part of the design. The unit comes with a Class 10 trip as standard. The SIRIUS 3RU11 features manual or automatic reset, adjustable current settings, and ambient compensation. A switch-position indicator also incorporates a test function which is used to simulate a tripped overload relay. A normally open and a normally closed auxiliary contact are included.

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Electronic Overload Relays

Electronic overload relays are another option for motor protection. The features and benefits of electronic overload relays vary but there are a few common traits. One advantage offered by electronic overload relays is a heaterless design. This reduces installation cost and the need to stock a variety of heaters to match motor ratings. Electronic relays offer phase loss protection. If a power phase is lost, motor windings can burn out very quickly. Electronic overload relays can detect a phase loss and disconnect the motor from the power source. This feature is not available on mechanical types of overload relays.

Furnas ESP 100 Electronic Overload Relay

A single ESP100 overload relay replaces at least six size ranges of heaters. Instead of installing heaters the full-load amperes (FLA) of the motor is set with a dial. The ESP100 overload relay illustrated below, for example, is adjustable from 9 to 18 amperes. NEMA Class 10, 20, and 30 trip curves are available for a variety of applications. The relay comes in either a manual or self-resetting version. Auxiliary contacts are available as an option.

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Siemens 3RB10 Electronic Overload Relay

The Siemens SIRIUS 3RB10 is an electronic overload relay with a design very similar to the ESP 100. The unit comes with a Class 10 or Class 20 trip. The 3RB10 features manual or automatic reset, adjustable current settings, and ambient compensation. A switch-position indicator also incorporates a test function which is used to simulate a tripped overload relay. A normally open and a normally closed auxiliary contact are included.

Siemens 3RB12 Electronic Overload Relay

In addition to heaterless construction and phase loss protection, the 3RB12 offers ground fault protection, phase unbalance, LED displays (ready, ground fault, and overload), automatic reset with remote capability, and selectable trip classes (5, 10, 15, 20, 25, or 30). The 3RB12 is self-monitoring and is provided with 2 normally open and 2 normally closed isolated auxiliary contacts.

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PROFIBUS DP

In any complex process the need for rapid information flow is critcal. PROFIBUS DP is an open communication system based upon international standards developed through industry associations. PROFIBUS DP allows the connection of several field devices, such as SIMOCODE-DP, on a single bus for communication to a PLC or computer. PROFIBUS DP is suitable as a replacement for costly parallel wiring.

3UF5 SIMOCODE-DP

The 3UF5 SIMOCODE-DP overload relay integrates with PROFIBUS-DP. SIMOCODE-DP protects the load against overload, phase failure, ground fault, and current imbalance. SIMOCODE-DP can be parametrized, controlled, observed, and tested from a central source such as a PC with WinSIMOCODE-DP/Professional installed, or a PLC with a PROFIBUS-DP communication processor. The 3UF50 basic unit can also be used as an autonomous solid-state overload relay for motor protection. A trip class in six steps from Class 5 to Class 30 can be selected. The basic unit (shown) is supplied with four inputs and four outputs. An available expansion unit provides eight additional inputs and four additional outputs.

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Review 3 1.

With an increase in current, heat will ____________ . a. increase b. decrease c. remain the same

2.

The National Electrical Code® defines overcurrent as any current in ____________ of the rated current of equipment or the ampacity of a conductor.

3.

An ____________ occurs when electrical equipment is required to work harder than it is rated.

4.

A Class __________ overload relay will trip an overloaded motor offline within 10 seconds at six times fullload amps. a. 10 b. 20 c. 30

5.

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A ____________ strip uses two dissimilar metals bonded together.

Manual Control

Manual control, as the name implies, are devices operated by hand. A simple knife switch, like the one shown in the following illustration, was the first manual-control device used to start and stop motors. The knife switch was eventually replaced with improved control designs, such as manual and magnetic starters.

Basic Operation

The National Electrical Code® requires that a motor control device must also protect the motor from destroying itself under overload conditions. Manual starters, therefore, consist of a manual contactor, such as a simple switch mechanism, and a device for overload protection. The following diagram illustrates a single-pole manual motor starter. Each set of contacts is called a pole. A starter with two sets of contacts would be called a two-pole starter.

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Two-Pole Manual Starter

Starters are connected between the power source and the load. For example, a two-pole or single-phase motor starter is connected to a motor. When the switch is in the “OFF” position, the contacts are open preventing current flow to the motor from the power source. When the switch is in the “ON” position, the contacts are closed and current flows from the power source (L1), through the motor, returning to the power source (L2).

This is represented with a line drawing and symbols as illustrated in the following drawing.

Low Voltage Protection

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Some manual motor starters offer low-voltage protection (LVP) as an option. LVP will automatically remove power from the motor when incoming power drops or is interrupted. The starter must be manually reset when power is restored. This protects personnel from potential injury caused by machinery that may otherwise automatically restart when power is restored.

SMF FractionalHorsepower Manual Starters

Siemens SMF fractional-horsepower starters provide overload protection and manual “ON/OFF” control for small motors. SMF starters are available in one- or two-pole versions suitable for AC motors up to 1 HP and 277 VAC. The two-pole version is suitable for DC motors up to 3/4 HP and 230 VDC. SMF manual starters are available in a variety of enclosures. A two-speed version is available.

MMS and MRS Manual Switches

Siemens MMS and MRS manual switches are similar to SMF starters but do not provide overload protection. MMS and MRS switches only provide manual “ON/OFF” control of single- or three-phase AC motors where overload protection is provided separately. These devices are suitable for use with three-phase AC motors up to 10 HP and 600 VAC and up to 1-1/2 HP and 230 VDC. The MMS and MRS manual switches are available in various enclosures. Two-speed and reversing versions are available.

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Furnas Class 11 Manual Starter and Manual Contactor

Furnas Class 11 manual starters use a melting-alloy overload relay with interchangeable heater elements and a manual reset. It has a maximum rating of 10 HP at 460 VAC (3Ø) and 5 HP at 230 VAC (1Ø). Class 11 manual starters are available in a complete line of general-purpose and industrial-duty enclosures. Class 11 manual starters may also be furnished with a low-voltage protection circuit. Class 11 manual contactors provide no overload protection.

3RV10 Motor Starter Protectors

3RV10 motor starter protectors (MSPs) are part of the Siemens SIRIUS 3R motor control product line. A thermal overload with a bimetal strip is used to provide overload protection with the 3RV10 motor starter protector. 3RV10 MSPs come in four frame sizes: 3RV101, 3RV102, 3RV103, and 3RV104. Frame 3RV101 3RV102 3RV103 3RV104

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Max Current at 460 VAC 12 Amps 25 Amps 50 Amps 100 Amps

Max HP at 460 VAC 7.5 20 40 75

The 3RV101 is available in both screw-terminal and CAGE CLAMP™ versions. The 3RV102, 3RV103, and 3RV104 are available with screw terminals.

CAGE CLAMP™

The CAGE CLAMP™ is available on many Siemens SIRIUS 3R products including the MSPs. To connect a wire, simply push an electrician blade screwdriver into the appropriate portal, insert the stripped end of the wire into the portal directly above, remove the screwdriver, and the wire is securely connected. CAGE CLAMP™ devices are especially beneficial in installations that are subject to vibration.

Enclosures and Options

Siemens 3RV10 MSPs are available in a variety of enclosures. Several options, such as indicator lights, are also available.

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Reversing Drum Controller

Manually operated drum controllers, like the Furnas Class 58 reversing drum controller, stop and change direction of reversible AC motors. Overload protection is not provided by the reversing drum controller and must be supplied by an external means. The Furnas Class 58 reversing drum controller is rated for 10 HP at 460 VAC. Another style of drum switch is used to change speed of multi-speed motors.

Master Switch

The Furnas Class 53 master switches provide single-handle control of hoists, cranes, oven pushers, and other equipment requiring speed steps of wound rotor or direct-current motors. Master switches are available with momentary or maintained contacts and up to five speed settings.

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Magnetic Contactors and Starters

Most motor applications require the use of remote control devices to start and stop the motor. Magnetic contactors, similar to the ones shown below, are commonly used to provide this function. Contactors are also used to control distribution of power in lighting and heating circuits.

Basic Contactor Operation

Magnetic contactors operate utilizing electromagnetic principles. A simple electromagnet can be fashioned by winding a wire around a soft iron core. When a DC voltage is applied to the wire, the iron becomes magnetic. When the DC voltage is removed from the wire, the iron returns to its nonmagnetic state. This principle is used to operate magnetic contactors.

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The following illustration shows the interior of a basic contactor. There are two circuits involved in the operation of a contactor: the control circuit and the power circuit. The control circuit is connected to the coil of an electromagnet, and the power circuit is connected to the stationary contacts.

The operation of this electromagnet is similar to the operation of the electromagnet we made by wrapping wire around a soft iron core. When power is supplied to the coil from the control circuit, a magnetic field is produced magnetizing the electromagnet. The magnetic field attracts the armature to the magnet, which in turn closes the contacts. With the contacts closed, current flows through the power circuit from the line to the load. When the electromagnet’s coil is deenergized, the magnetic field collapses and the movable contacts open under spring pressure. Current no longer flows through the power circuit.

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The following schematic shows the electromagnetic coil of a contactor connected to the control circuit through a switch (SW1). The contacts of the contactor are connected in the power circuit to the AC line and a three-phase motor. When SW1 is closed, the electromagnetic coil is energized, closing the “M” contacts and applying power to the motor. Opening SW1 deenergizes the coil and the “M” contacts open, removing power from the motor.

Overload Relay

Contactors are used to control power in a variety of applications. When applied in motor-control applications, contactors can only start and stop motors. Contactors cannot sense when the motor is being loaded beyond its rated conditions. They provide no overload protection. Most motor applications require overload protection. However, some smaller-rated motors have overload protection built into the motor (such as a household garbage disposal). Overload relays, similar to the one shown below, provide this protection. The operating principle, using heaters and bimetal strips, is similar to the overloads discussed previously.

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Motor Starter

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Contactors and overload relays are separate control devices. When a contactor is combined with an overload relay, it is called a motor starter.

Motor Starter in a Control Circuit

The following diagram shows the electrical relationship of the contactor and overload relay. The contactor, highlighted with the darker grey, includes the electromagnetic coil, the main motor contacts, and the auxiliary contacts. The overload relay, highlighted by the lighter grey, includes the “OL” heaters and overload contacts. The contactor and the overload relay have additional contacts, referred to as auxiliary contacts, for use in the control circuit. In this circuit a normally closed “OL” contact has been placed in series with the “M” contactor coil and L2. A normally open “M” auxiliary contact (“Ma”) has been placed in parallel with the “Start” pushbutton.

Review 4 1.

A starter with two sets of contacts would be called a ____________ -pole starter.

2.

____________ will automatically disconnect power from the motor when incoming power drops or is interrupted.

3.

The Furnas Class 11 motor starter protects motors up to ____________ HP at 460 VAC and ____________ HP at 230 VAC.

4.

The 3RV102 motor starter protector protects motors up to ____________ HP at 460 VAC.

5.

When a contactor is combined with an overload relay, it is called a ____________ ____________ .

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Starter Ratings

Starter contactors are rated according to size and type of load they handle. The National Electrical Manufacturers Association (NEMA) and the International Electrotechnical Commission (IEC) are two organizations that rate contactors and motor starters. NEMA is primarily associated with equipment used in North America. IEC, on the other hand, is associated with equipment sold in many countries including the United States. International trade agreements, market globalization, and domestic and foreign competition have made it important for controls manufacturers to be increasingly aware of international standards. NEMA

NEMA ratings are maximum horsepower ratings, according to the National Electrical Manufacturers Association ICS2 standards. NEMA starters and contactors are selected according to their NEMA size. These sizes range from size 00 to size 9. NEMA Size 00 0 1 2 3 4 5 6 7 8 9

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Continuous HP 230 VAC HP 460 VAC Amp Rating 9 1 2 18 3 5 27 7 10 45 15 25 90 30 50 135 50 100 270 100 200 540 200 400 810 300 600 1215 450 900 2250 800 1600

NEMA motor-control devices have generally become known for their very rugged, heavy-duty construction. Because of their rugged design NEMA devices are physically larger than IEC devices. NEMA motor starters and contactors can be used in virtually any application at their stated rating, from simple “ON” and “OFF” applications to more-demanding applications that include plugging and jogging. To select a NEMA motor starter for a particular motor one need only know the horsepower and voltage of the motor. If there is considerable plugging and jogging duty involved, however, even a NEMA-rated device will require some derating. Motor Matched Sizes

Siemens also has what are called Motor Matched sizes available on some Siemens motor starters. The ratings for these devices fall in between the ratings of normal NEMA sizes. This allows the user to more closely match the motor control to the actual application. The following table shows Motor Matched sizes available. MM Size Continuous HP 230 VAC HP 460 VAC AMP Rating 1¾ 2½ 3½ 4½

IEC

40 60 115 210

10 20 40 75

15 31 75 150

Not all applications require a heavy-duty industrial starter. In applications where space is more limited and the duty cycle is not severe, IEC devices represent a cost-effective solution. IEC devices are rated for maximum operational current as specified by the International Electrotechnical Commission in publication IEC 158-1. IEC does not specify sizes. Utilization categories are used with IEC devices to define the typical duty cycle of an IEC device. AC-3 and AC-4 are the categories of most interest for general motor-starting applications. Utilization Category

IEC Category Description

AC1

Non-inductive or slightly inductive loads.

AC2

Starting of slip-ring motors

AC3

Starting of squirrel-cage motors and switching off only after the motor is up to speed. (Make LRA, Break FLA)

AC4

Starting of squirrel-cage motors with inching and plugging duty. Rapid Start/Stop. (Make and break LRA)

AC11

Auxiliary (control) circuits.

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Definite Purpose

Definite Purpose (DP) contactors have certain characteristics which must be taken into consideration. DP contactors were designed for specific applications where the operating conditions are clearly defined. These operating conditions include full load amps, locked rotor amps, noninductive amps (resisitive load), number of power poles, duty cycle, and the total number of expected operations. DP contactors are sized by the motor full-load amps (FLA) and locked rotor amps (LRA). FLA is the amount of current the motor draws at full speed, under full mechanical load, at rated voltage. LRA is the maximum current the motor will draw at the instant full-line voltage is applied to the motor. DP contactors are well suited for loads found in the following areas: • Heating, Ventilating, and Air Conditioning (HVAC) • Farm Equipment and Irrigation • Environmental Control Systems • Office Equipment • Pool and Spa Controls • Welding Equipment • Medical Equipment • Food-Service Equipment

Other Organizations

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There are several other organizations that have developed standards and tests for electrical equipment. Underwriters Laboratory (UL), for example, specifies a maximum horsepower rating for which a contactor can be used. The contactor is tested by Underwriters Laboratory using test procedure U.L. 508. All Siemens contactors are rated in accordance with at least one of the previous organizations’ test procedures. Some carry multiple ratings. For example, Furnas INNOVA starters meet or exceed NEMA and UL standards. Siemens SIRIUS starters meet or exceed NEMA, IEC, and UL standards.

Furnas INNOVA PLUS Starters

Furnas INNOVA PLUS™ starters are available in NEMA sizes 0 through 4. They are available up to 100 HP. Furnas INNOVA PLUS starters are available with Class 10 or 20 ambientcompensated bimetal overload relays.

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ESP100 Starters

The Furnas ESP100™ starters use the same contactor as the INNOVA PLUS™ starters. The ESP100 starters are supplied with a Class 10, 20, or 30 ESP100 solid-state overload relay. The ESP100 overload relay protects 3Ø motors with FLA of ¼ ampere through 135 amperes. From ¼ ampere to 10 amperes the overload has a 4:1 FLA range, i.e.; 2½ - 10 amperes. Above 10 amperes the range is 2:1. The ESP100 overload relay illustrated below, for example, is adjustable from 9 to 18 amperes.The ESP100 also protects the motor against phase loss. The ESP100 trips within three seconds of loss of one of the power-supply phases.

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SIRIUS Type 3R Starters

SIRIUS 3R is a complete modular, building-block system. The system includes a structured range of contactors and overload relays covering loads up to 95 amps in four frame sizes. These four frame sizes are referred to as S00 (12A), S0 (25A), S2 (50A), and S3 (95A). A feature of the SIRIUS product line is a narrow mounting width. An S3 contactor rated at 75 HP, for example, is only 70mm (2.75”). SIRIUS 3R contactors and overload relays can operate in ambient temperatures up to 140°F (60°C). This, along with the smaller size, allows more units to be packed into a panel without overheating the components.

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CAGE CLAMP™

Size S00 contactors and overload relays are available with CAGE CLAMP™ connections on power and control-circuit terminals. Size S0, S2, and S3 contactors and overload relays have CAGE CLAMP™ connections on the control-circuit terminals only.

Overload Relays

SIRIUS 3R overload relays provide Class 10 overcurrent protection for both AC and DC motors. Ambient-compensated bimetal strips prevent the overload relay from nuisance tripping when the panel temperature is higher than the ambient temperature of the motor. The design of the overload relay also includes a differential trip bar that causes the unit to trip faster in the event of a phase-loss condition. An optional remote-reset module (not shown) is available.

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World Series Type 3TF Starters

The World Series starters are supplied with a type 3TF contactor and overload relay. World Series starters are available in horsepower ratings from 100 to 500 HP at 460 VAC. Auxiliary contacts are provided for use in the control circuit. World Series type 3TF contactors are available with various enclosures. Additional auxiliary contacts can be added. Coil voltages for the electromagnetic coil range from 24 to 600 VAC. The overload relay is a Class 10 relay that uses a bimetal strip unit and heater element to detect overloads. Each phase monitors current. The unit has a full-load amps adjustment, test button, and reset button. The full-load amps adjustment corresponds to the range of the motor full-load ampere rating. The test button is to ensure the overload relay is functioning properly. The reset button is used to reset a trip. It can be either automatic or manual reset. There is also a trip indicator.

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Overload Relay Selection

The following chart is useful in selecting the correct contactor and overload-relay combination. The chart reflects the maximum horsepower rating using Underwriters Laboratory test procedure U.L. 508 and the appropriate overload relay. Contactor Max HP (at Overload 460 VAC) Relay 3TF50 100 3UA60 3TF51 100 3UA61 3TF52 125 3UA62 3TF53 150 3UA62 3TF54 200 3UA66 3TF55 250 3UA66 3TF56 300 3UA66 3TF57 400 3UA68 3TF68 500 3UA68

Review 5

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1.

____________ is an organization primarily associated with rating equipment used in North America and ____________ is associated with rating equipment used in many countries including the U.S.

2.

A NEMA Size ____________ starter is rated for 200 HP at 460 volts .

3.

IEC utilization category ____________ applications are described as the starting of squirrel-cage motors and switching off only after a motor is up to speed.

4.

Furnas INNOVA PLUS™ starters are available in NEMA sizes 0 through ____________ .

5.

The ESP100 trips within ____________ seconds of loss of one of the power-supply phases.

6.

The maximum load current of a size S2 SIRIUS 3R starter is ____________ amps.

7.

The correct overload relay for a 3TF54 contactor is ____________ .

Multi-Speed and Reversing Starters

Full-voltage AC magnetic multi-speed controllers are designed to control squirrel-cage induction motors for operation at two, three, or four different constant speeds, depending on motor construction. The speed of a constant-speed motor is a function of the supply frequency and the number of poles and is given in the following formula:

The speed in RPM is the synchronous speed or the speed of the rotating magnetic field in the motor stator. Actual rotor speed is always less due to slip. The design of the motor and the amount of load applied determine the percentage of slip. This value is not the same for all motors. A motor with four poles on a 60 hertz AC line has a synchronous speed of 1800 RPM. This means that, after allowing for slip, the motor is likely to run at 1650 to 1750 RPM when loaded.

An induction motor with two poles on a 60 hertz AC line, however, would run at twice that speed. When motors are required to run at different speeds, the motor’s torque or horsepower characteristics will change with a change in speed. The proper motor must be selected and correctly connected for the application. In these applications, there are three categories. Constant Torque (CT) Variable Torque (VT) Constant Horsepower (CHP)

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Separate-Winding

There are two basic methods of providing multi-speed control using magnetic starters: separate-winding motors and consequent-pole motors. Separate-winding motors have a separate winding for each speed. The speed of each winding depends on the number of poles. The low-speed winding is wound for more poles than the high-speed winding.The motor cost is higher than consequent pole, but the control is simpler. There are many ways multi-speed motors can be connected depending on speed, torque, and horsepower requirements. The following schematic shows one possible connection of a twospeed, two-winding, wye-connected motor.

Consequent-Pole Motors

Consequent-pole motors have a single winding for two speeds. Taps can be brought from the winding for reconnection for a different number of poles. Two-speed, consequent-pole motors have one reconnectable winding. Low speed of a twospeed, consequent-pole motor is one half the speed of high speed. Three-speed motors have one reconnectable winding and one fixed winding. Four-speed motors have two reconnectable windings.

Speed Selection

There are three control schemes of speed selection for multispeed motors: selective control, compelling control, and progressive control. Selective control permits motor starting at any speed and to move to a higher speed the operator depresses the desired speed pushbutton. Compelling control requires the motor to be started at the lowest speed, then the operator must manually increment through each speed step to the desired speed. With progressive control the motor is started at the lowest speed and automatically increments to the selected speed.

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Reversing

Many applications require a motor to run in both directions. In order to change the direction of motor rotation, the direction of current flow through the windings must be changed. This is done on a three-phase motor by reversing any two of the three motor leads. Traditionally T1 and T3 are reversed. The following illustration shows a three-phase reversing motor circuit. It has one set of forward (F) contacts controlled by the “F” contactor, and one set of reverse (R) contacts controlled by the “R” contactor.

When the “F” contacts are closed, current flows through the motor causing it to turn in a clockwise direction.

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When the “R” contacts are closed, current flows through the motor in the opposite direction causing it to rotate in a counterclockwise direction. Mechanical interlocks prevent both forward and reverse circuits from being energized at the same time.

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Reduced-Voltage Starting

Full-Voltage Starting

The most common type of motor starting is full-voltage starting. The motor is placed directly across the line with this method.

With this type of starter the motor receives the full-line voltage. When a motor is started with full voltage, starting current can be as high as 600% of full-load current on standard squirrel cage motors. It can be even higher on high efficiency motors. There are situations where this method of starting is not acceptable. On large motors the high starting current is reflected back into the power lines of the electric utility, causing lights to flicker and in more serious situations can cause computers to malfunction. Many power companies in the U.S. require reduced-voltage starting on large-horsepower motors.

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Another potential problem with applying full-voltage starts is the high torque developed when power is first applied to the motor. This can be as high as 175% to 200% of full-load torque on a standard NEMA B type motor. Many applications require the starting torque to be applied gradually. A conveyor belt, for example, requires the starting torque to be applied gradually to prevent belt slipping or bunching.

Reduced-Voltage Starting

In general, starting methods which deviate from full-voltage starting by providing a lower starting voltage are referred to as reduced-voltage starting. Reduced-voltage starting should be used when it is necessary to limit the initial inrush of current or it is desired to reduce the starting torque of a motor. Reduced-voltage starting reduces the starting voltage of an induction motor with the purpose of confining the rate of change of the starting current to predetermined limits. It is important to remember that when the voltage is reduced to start a motor, current is also reduced, which also reduces the amount of starting torque a motor can deliver. Several methods are available for reduced-voltage starting. The application or the type of motor generally dictates the method to use. A few of the methods offered by Siemens are described in the following paragraphs.

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Autotransformer ReducedVoltage Starters

Autotransformer reduced-voltage starters provide the highest starting torque per ampere of line current and is one of the most effective means of starting a motor for an application in which starting current must be reduced with a minimum sacrifice of starting torque. Autotransformers have adjustable taps to reduce starting voltage to 50%, 65%, or 80% of full-line voltage. Applications: Blowers, Pumps, Compressors

Part-Winding Starters

Part-winding, reduced-voltage starters are used on motors with two separate parallel windings on the stator. The windings used during start draw about 65 - 80% of rated locked rotor current. During run each winding carries approximately 50% of the load current. Part-winding, reduced-voltage starters are the leastexpensive type of reduced-voltage starters and use a very simplified control circuit. However, they require special motor design and are not suitable for high inertia loads. There is no adjustment of current or torque. Applications: Pumps, Fans, Refrigeration, Compressors

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Wye-Delta Starters

Wye-delta, reduced-voltage starters are applicable only with motors having stator windings not connected internally and all six motor leads available. Connected in a wye configuration, the motor starts with reduced starting line current. The motor is reconfigured to a delta connection for run. This type of starter is a good method for applications requiring frequent starts. The starting torque is lower compared to other methods of reduced voltage starters. Applications: Central Air Conditioning Equipment, Compressors

Primary Resistance Starter

This is a simple and effective starting method. The motor is initially energized through a resistor in each of the three incoming lines. Part of the voltage is dropped through the resistors. The motor receives 70% to 80% of the full-line voltage. As the motor picks up speed, the motor sees more of the line voltage. At a preset time a time-delay relay closes a separate set of contacts, shorting out the resistors and applying full voltage to the motor. This type of reduced voltage starting is limited by the amount of heat the resistors can dissipate. Applications: Conveyors, Belt-Driven and Gear Drive Equipment

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Review 6 1.

____________ - ____________ ____________ is a method of providing multi-speed control that utilize taps brought out from a reconnectable winding.

2.

With ____________ ____________ the motor is started at the lowest speed and automatically increments to the selected speed.

3.

In general, starting methods which deviate from fullvoltage starting by providing a lower starting voltage are referred to as ___________ ___________ ___________ .

4.

____________ reduced-voltage starters have adjustable taps to reduce starting voltage to 50%, 65%, or 80% of full line voltage.

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Solid-State Reduced-Voltage Controllers

Solid-state or soft-start controllers also use reduced voltage starting. These controllers are more advanced and allow greater control of the starting, running, and stopping of an AC motor than the electromechanical starters discussed in the previous section. Reduced-voltage electromechanical starters start a motor in steps by first applying a reduced voltage followed by full voltage. Solid-state reduced-voltage controllers, however, can apply voltage gradually from some low intial volatge to 100% voltage. The following graph compares a solid-state reduced-voltage controller to a full- voltage (across-the-line) starter. By applying voltage gradually, the motor experiences reduced inrush current and speed is accelerated smoothly. In addition, just enough torque can be applied to start and accelerate the motor. This is beneficial for loads that have problems with the initial jerk and rapid acceleration of across-the-line starting.

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SIRIUS 3R Soft-Start Controls

SIRIUS 3R controllers provide gradual voltage starting and stopping.SIRIUS 3R soft-start controls are compact and compliment the rest of the SIRIUS line. The compact design allows the controls to be DIN rail mounted and integrated with any combination of other controls, such as, overloads, contactors, and motor starter protectors. SIRIUS 3R soft-start controls are available for motors up 75HP at 575 volts. A cost saving advantage of the SIRIUS 3R controller is the ability of one model to handle voltages from 200 to 460 volts.

SIKOSTART

SIKOSTART controllers are used in applications of up to 1000 horsepower. Like the SIRIUS 3R, SIKOSTART provides gradual voltage starting and stopping.

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SIKOSTART Wired Inline

SIKOSTART can easily be wired conventionally in line with the motor windings. In this configuration the controller sees full motor current.

SIKOSTART Wired Inside the Delta

On motors that have all leads available, the SIKOSTART controller can also be wired inside the delta connection of the motor. This offers a significant cost advantage. Current inside the delta of an AC motor is approximately 57% of nominal motor current. With this configuration a smaller SIKOSTART controller can be selected.

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Pilot Devices

A pilot device directs the operation of another device (pushbuttons and selector switches) or indicates the status of the operating system (pilot lights). This section discusses Siemens 3SB and Furnas Class 51/52 pushbuttons, selector switches, and pilot lights. 3SB devices are available in 22 mm diameters. Class 51/52 pilot devices are available in 30 mm diameter. The diameter refers to the size of the knockout hole required to mount the devices. Class 51 devices are rated for hazardous locations environments such as Class I, Groups C and D and Class II, Groups E, F, and G. Class 52 devices are heavy duty for harsh, industrial environments. Bifurcated Contacts

Whether one chooses the 3SB or the Class 51/52 pilot devices, the fine silver contacts have a 10 A/600 V continuous-current rating and can be used on solid state equipment. The 3SB and the Class 51/52 devices use bifurcated movable contacts. The design of the bifurcated contacts provides four different pathways for current to flow, thus improving contact reliability.

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Pushbuttons

A pushbutton is a control device used to manually open and close a set of contacts. Pushbuttons are available in a flush mount, extended mount, with a mushroom head, illuminated or nonilluminated. Pushbuttons come with either normally open, normally closed, or combination contact blocks. The Siemens 22 mm pushbuttons can handle up to a maximum of 6 circuits. The Furnas 30 mm pushbutton can handle up to a maximum fo 16 circuits.

Normally Open Pushbuttons

Pushbuttons are used in control circuits to perform various functions. For example, pushbuttons can be used when starting and stopping a motor. A typical pushbutton uses an operating plunger, a return spring, and one set of contacts. The following drawing illustrates a normally open (NO) pushbutton. Normally the contacts are open and no current flows through them. Depressing the button causes the contacts to close. When the button is released, the spring returns the plunger to the open position.

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Normally Closed Pushbuttons

Normally closed (NC) pushbuttons, such as the one shown below, are also used to open and close a circuit. In the pushbutton’s normal position the contacts are closed to allow current flow through the control circuit. Depressing the button opens the contacts preventing current flow through the circuit. These types of pushbuttons are momentary contact pushbuttons because the contacts remain in their activated position only as long as the plunger is held depressed.

Pushbuttons are available with variations of the contact configuration. For example, a pushbutton may have one set of normally open and one set of normally closed contacts so that when the button is depressed, one set of contacts is open and the other set is closed. By connecting to the proper set of contacts, either a normally open or normally closed situation exists. Using Pushbuttons in a Control Circuit

The following line diagram shows an example of how a normally open and a normally closed pushbutton might be used in a control circuit.

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Momentarily depressing the “Start” pushbutton completes the path of current flow and energizes the “M” contactor’s electromagnetic coil.

Holding Circuit Three-Wire Control

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This closes the associated normally open “M” and “Ma” contacts. When the “Start” pushbutton is released a holding circuit exists to the “M” electromagnetic coil through the auxiliary contacts “Ma” . The motor will run until the normally closed “Stop” pushbutton is depressed, breaking the path of current flow to the “M” electromagnetic coil and opening the associated “M” and “Ma” contacts. This is referred to as threewire control because there are three wires or three connection points required to connect the “Start” and “Stop” pushbuttons and the holding circuit (“Ma”). An advantage to three-wire control is low-voltage protection. If an overload causes the “OL” contacts in the control circuit to open, the “M” coil is deenergized and the motor shut down. When the overload is cleared, the motor will not suddenly restart on its own. An operator must depress the “Start” button to restart the motor.

Two-Wire Control

In comparison, a two-wire control has only two connection points for the “Start/Stop” circuit. When the contacts of the control device close, they complete the coil circuit of the contactor, causing it to be energized and connect the load to the line through the power contacts. When the contacts of the control device open, the power is removed from the motor and it stops. A two-wire control circuit provides low-voltage release but not low-voltage protection. This means that in the event of a power loss the contactor will deenergize, stopping the motor. This is low-voltage release. However, when power is restored, the motor will restart without warning if the control device is still closed. This type of control scheme is used for remote or inaccessible installations such as water-treatment plants or pumping stations. In these applications it is desireable to have an immediate return to service when power is restored.

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Selector Switches

Selector switches are also used to manually open and close contacts. Selector switches can be maintained, spring return or key operated. Selector switches are available in two-, three-, and four-position types. The basic difference between a push button and a selector switch is the operator mechanism. With a selector switch the operator is rotated to open and close contacts. Contact blocks used on pushbuttons are interchangeable with those on used on selector switches. Selector switches are used to select one of several circuit possibilities such as manual or automatic operation, low or high speed, up or down, right or left, and stop or run. The Siemens 22 mm selector switches can handle up to a maximum of 6 circuits. The Furnas 30 mm selector switch can handle up to a maximum of 16 circuits.

Two Position Selector Switch

In the following example PL1 is connected to the power source when the switch is in position 1. PL2 is connected to the power source when the switch is in position 2. In this circuit either PL1 or PL2 would be on at all times. If there were only one load, then the selector switch could be used as an On/Off switch.

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Contact Truth Tables

There are two accepted methods of indicating contact position of a selector switch in a circuit. The first method uses solid and dashed lines to denote contact position as shown in the previous example. In the second method truth tables, also known as target tables, are used. Each contact is marked with a letter. An “X” in the truth table indicates which contacts are closed for a given switch position. In this example contact A is closed, connecting PL1 to the power source, when the switch is in position 1. Contact B is closed, connecting PL2 to the power source, when the switch is in position 2.

Three-Position

A three-position selector switch can be used to select either of two sets of contacts or to disconnect both sets of contacts. Hand/Off/Auto is a typical application for a three-position selector switch used for controlling a pump. In the Hand (manual) position the pump will start when the Start pushbutton is pressed. The pump can be stopped by switching the switch to the Off position.The liquid level switch has no effect in either the Hand or Off position. When the selector switch is set to Auto, the pump will be controlled by the liquid-level switch. At a predetermined level the liquid level switch closes, starting the pump. At a predetermined level the liquid level switch opens, stopping the pump.

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Pilot Lights

Pilot lights provide visual information at a glance of the circuit’s operating condition. Pilot lights are normally used for “ON/OFF” indication, caution, changing conditions, and alarm signaling.

Pilot lights come with a color lens, such as red, green, amber, blue, white, or clear. A red pilot light normally indicates that a system is running. A green pilot light normally indicates that the system is off or deenergized. For example, a red pilot light located on a control panel would give visual indication that a motor was running. A green pilot light would give visual indication that a motor was stopped.

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Using a Pilot Light in a Control Circuit

In the following line diagram, a red pilot light is connected in parallel with the “M” electromagnetic coil.

When the coil is energized, the light will illuminate to indicate the motor is running. In the event the pilot light burns out the motor will continue to run.

In the following line diagram a green pilot light is connected through a normally closed “M” auxiliary contact (Mb). When the coil is deenergized, the pilot light is on to indicate the motor is not running.

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Depressing the “Start” pushbutton and energizing the “M” contactor opens the normally closed “Mb” contacts, turning the light off.

Signalling Columns

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Signalling columns can be mounted locally on individual machines, making it possible for the operating personnel to monitor production stations from a distance. Individual modules, or elements, are connected together. Various visual elements are available, including strobe lights, steady or flashing lights, and incandescent or LED lights. Lenses for the light elements are available in red, yellow, green, blue, and clear. Audible elements for the 8WD43 include a siren and a buzzer. Audible elements for the 8WD42 include a buzzer. In addition, a communication element is available allowing the signalling column to communicate with PLCs or computers through the Actuator Sensor Interface (ASI) network. Up to 10 elements can be used on a signalling column.

Review 7 1.

A ____________ ____________ directs the operation of another device.

2.

Which of the following circuits represents a two-wire control and which represents a three-wire control?

3.

Pilot lights provide ____________ information of the circuit’s operating condition.

4.

A ____________ pilot light normally indicates a motor is running and a ____________ pilot light normally indicates a motor is stopped.

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Control Transformers

It is often desirable to operate the control circuit at a lower voltage than the power circuit. Control transformers are used to step a voltage down to a lower level. Siemens control transformers are available in various primary and secondary voltages from 50 to 5000 VA.

In the following example, the power circuit is 460 VAC. A control transformer is used to step the voltage down to 24 VAC for use in the control circuit. The electromagnetic coil voltage must be rated for 24 VAC. Fuses on the primary and secondary windings of the transformer provide overcurrent protection.

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Control Relays

Relays are widely used in control circuits. They are used for switching multiple control circuits and for controlling light loads such as starting coils, pilot lights, and audible alarms.

Relay Operation

The operation of a control relay is similar to a contactor. In the following example a relay with a set of normally open (NO) contacts is used. When power is applied from the control circuit, an electromagnetic coil is energized. The resultant electromagnetic field pulls the armature and movable contacts toward the electromagnet closing the contacts. When power is removed, spring tension pushes the armature and movable contacts away from the electromagnet opening the contacts.

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Contact Arrangement

A relay can contain normally open, normally closed, or both types of contacts. The main difference between a control relay and a contactor is the size and number of contacts. The contacts in a control relay are relatively small because they need to handle only the small currents used in control circuits. There are no power contacts. Also, unlike a contactor, each contact in a control relay controls a different circuit. In a contactor, they all control the starting and stopping of the motor. Some relays have a greater number of contacts than are found in the typical contactor. The use of contacts in relays can be complex. There are three words which must be understood when dealing with relays.

Pole

Pole describes the number of isolated circuits that can pass through the relay at one time. A single-pole circuit can carry current through one circuit. A double-pole circuit can carry current through two circuits simultaneously. The two circuits are mechanically connected so that they open or close at the same time.

Throw

Throw is the number of different closed-contact positions per pole. This is the total number of different circuits each pole controls.

The following abbreviations are frequently used to indicate contact configurations: SPST SPDT DPST DPDT

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Single-Pole, Single-Throw Single-Pole, Double-Throw Double-Pole, Single-Throw Double-Pole, Double-Throw

Break

Break is the number of separate contacts the switch contacts use to open or close individual circuits. If the switch breaks the circuit in one place, it is a single-break. If the relay breaks the circuit in two places, it is a double-break.

The following illustrates various contact arrangements.

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Interposing a Relay

The following line diagram illustrates one way a control relay might be used in a circuit. A 24 VAC coil may not be strong enough to operate a large starter. In this example the electromagnetic coil of the “M” contactor selected is rated for 460 VAC. The electromagnetic coil of the control relay (CR) selected is 24 VAC. This is known as interposing a relay.

When the “Start” pushbutton in line 2 is momentarily depressed, power is supplied to the control relay (CR).

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The “CR” contacts in lines 1and 2 close. The “CR” contacts in line 2 maintain the start circuit. The “CR” contacts in line 1 complete the path of current to the “M” motor starter. The “M” motor starter energizes and closes the “M” contacts in the power circuit, starting the motor. Depressing the “Stop” pushbutton deenergizes the “CR” relay and “M” motor starter.

SIRIUS 3RH11 Control Relays

Siemens has a complete line of industrial-control relays. SIRIUS 3RH11 relays are available with screw terminal or Cage Clamp. The screw terminal version is shown in the following illustration. Four contacts are available in the basic device. Four additional contacts in the form of a snap-on device can be added to the front of the relay. Some SIRIUS 3RH11 relays are specifically designed to interface directly with PLCs and other solid-state control devices. SIRIUS 3RH11 relays are rated for switching both AC and DC circuits. Coil voltages range from 12 VDC to 230 VDC and 24 VAC to 600 VAC.

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General-Purpose Relays (Plug-In Relays)

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Siemens also manufactures a variety of general-purpose relays for socket and flange mounting. Coil voltages are available in 24 VAC, 120 VAC or 24 VDC. The biggest benefit of this type of relay is all the wiring stays in place with the socket if the relay needs to replaced with a new one.

Timing Relays

Timing relays, such as the SIRIUS 3RP timing relays, are used in control switching operations involving time delay. SIRIUS 3RP1 timing relays have timing ranges available from .05 seconds to 10 hours. SIRIUS 3RP15 have timing ranges from .05 seconds to 100 hours.

Time Delay

A timing relay has two major functions: On-delay and Off-delay timing. An arrow is used to denote the function of the timer. An arrow pointing up indicates an On-delay timing action. An arrow pointing down indicates an Off-delay timing action.

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On-delay and Off-delay timers can turn their connected loads on or off, depending on how the timer’s output is wired into the circuit. On-delay indicates that once a timer has received a signal to turn on, a predetermined time (set by the timer) must pass before the timer’s contacts change state. Off-delay indicates that once a timer has received a signal to turn off, a predetermined time (set by the timer) must pass before the timer’s contacts change state. On-Delay, Time Closed

The following is an example of On-delay, timed closed. For this example a set of normally open (NO) contacts is used. This is also referred to as normally open timed closed (NOTC). The timing relay (TR1) has been set for an On-delay of 5 seconds.

When S1 is closed, TR1 begins timing. When 5 seconds has elapsed, TR1 will close its associated normally open (NO) TR1 contacts, illuminating pilot light PL1. When S1 is open, deenergizing TR1, the TR1 contacts open immediately, extinguishing PL1.

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On-Delay, Timed Open

The following is an example of On-delay, timed open. For this example a set of normally closed (NC) contacts is used. This is also referred to as normally closed, timed open (NCTO). PL1 is illuminated as long as S1 remains open. The timing relay (TR1) has been set for an ON delay of 5 seconds.

When S1 is closed, timing relay TR1 is energized. After a timed delay of 5 seconds, the associated normally closed TR1 contacts open, extinguishing PL1. When S1 is open, deenergizing TR1, the TR1 contacts close immediately, illuminating PL1.

Off-Delay, Timed Open

The following is an example of Off-delay, timed open. For this example a set of normally open contacts (NO) is used. This is also referred to as normally open, timed open (NOTO). The timing relay (TR1) has been set for an off delay of 5 seconds. Closing S1 energizes TR1 causing its associated normally open TR1 contacts to close immediately, illuminating PL1.

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When S1 is opened, TR1 begins timing. When 5 seconds has elapsed, TR1 will open its associated normally open contacts, extinguishing pilot light PL1.

Off-Delay, Timed Closed

The following is an example of Off-delay, timed closed. For this example a set of normally closed (NC) contacts is used. This is also referred to as normally closed, timed closed (NCTC). The timing relay (TR1) has been set for 5 seconds. PL1 is on. Closing S1 energizes TR1 causing its associated contacts to open immediately, extinguishing PL1.

When S1 is opened, timing relay TR1 is deenergized. After 5 seconds, the associated normally closed contacts close, illuminating PL1.

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Instantaneous Contacts

Timing relays can also have normally open or normally closed instantaneous contacts. In the following example, when switch S1 is closed, the TR1 instantaneous contacts will close immediately, illuminating PL1. After a preset time delay the TR1 timing contacts will close, illuminating PL2.

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Pressure Switches

Pressure switches are control devices that respond to changes in pressure of liquid or air. The liquid or air is referred to as fluid pressure. They open or close electrical contacts in response to pressure changes by either turning on or off a motor, opening or closing louvers, or signaling a warning light or horn. For loads up to 5 HP the pressure switches may handle the current directly. For larger loads the pressure switch is used to energize relays, contactors, or motor starters, which then energize the load.

Pressure Switch Components

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The basic components of a pressure switch are illustrated below. Electrical contacts are operated by the movement of a diaphragm against the force of a spring. The contacts may be normally open (NO) or normally closed (NC). The spring setting determines how much fluid pressure is required to operate the contacts.

Application

Pressure switches are frequently used to maintain a specified pressure range in a storage tank. Storage tanks can be used to hold a liquid, such as water, or a gas, such as air.

Operation

In this example a normally closed pressure switch is used. The pump starts as soon as power is applied to the circuit. When the pressure in the storage tank has reached a predetermined level, the contacts in the pressure switch open, removing power from the pump motor. As the contents of the storage tank are used, the pressure in the tank decreases. At a predetermined level the pressure switch will close its contacts, applying power to the pump motor.

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Pressure Range

Pressure switches are designed to operate within a specified pressure range, usually given in pounds per square inch (PSI). In the following example, a Furnas Class 69ES water pressure switch operates within a range of 10 to 80 PSI. The minimum close, or cut-in pressure, is 10 PSI. This is the point at which fluid pressure on the diaphragm causes the contacts to close. The maximum open, or cut-out pressure, is 80 PSI. This is the point at which fluid pressure on the diaphragm causes the contacts to open. Pressure differential is the difference between these two settings. The Furnas Class 69ES pressure switch can have a differential range of 15-25 PSI. In this example the cut-in pressure has been set to 30 PSI. The cut-out pressure has been set to 50 PSI. The pressure differential is 20 PSI. The pressure switch will regulate the pressure between 30 and 50 PSI.

Reverse Action

Reverse action pressure switches cut-in on a rising pressure. They are designed to ground the ignition on gas engine driven pumps and compressors when the maximum pressure has been reached. In the following example a Furnas Class 69WR5 reverse action pressure switch has been selected. The 69WR5 has a minimum open (cut-out) of 10 PSI and a maximum close (cut-in) of 80 PSI. The differential is set so that the switch opens at 30 PSI and closes at 50 PSI.

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LOGO! Logic Module

LOGO! is a logic module used to perform control tasks. The module is compact and user friendly, providing a cost-effective solution for the end user.

Hard-Wired Control

In the past, many of these control tasks were solved with contactor or relay controls. This is often referred to as hard-wired control. Circuit diagrams had to be designed and electrical components specified and installed. A change in control function or system expansion could require extensive component changes and rewiring.

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Many of the same tasks can be performed with LOGO!. Initial hard-wiring, though still required, is greatly simplified. Modifying the application is as easy as changing the program via the keypad located on the front of the LOGO!. Likewise, control programs can be created and tested before implementation via a PC software program. Once the program is performing per specification, the transfer to LOGO! is as simple as plugging in a cable. Basic LOGO! Operation

LOGO! accepts a variety of digital inputs, such as pushbuttons, switches, and contacts. LOGO! makes decisions and executes control instructions based on the user-defined program. The instructions control various outputs. The outputs can be connected to virtually any type of load such as relays, contactors, lights, and small motors.

Design Features

LOGO! is available in many different versions for different supply voltages (12 VDC, 24 VDC, 24 VAC or 115/230 VAC). All models have: • • • • • • • • • •

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Relay outputs with maximum 10 amp output current (not LOGO! 24/24L models) Integrated clock (not LOGO! 24/24L models) Integrated display Integrated keypad Integrated basic and special functions Integrated EEPROM for storing programs and setpoints Optional program module Yellow Module for simple program dupication Red Module for program backup and protection Basic AND, OR, NOT, NAND, NOR, and XOR functions AND and NAND functions with positive and negative edge detection Special ON delay, latching ON delay, OFF delay, pulse relay, latching relay, clock pulse generator, and counter (up/ down) functions (total of 21 special functions)

Basic version features: • •

Six digital inputs, four digital outputs for AC models Eight digital inputs, four digital outputs for DC models with two inputs capable of accepting analog inputs

Pure version features: •

LOGO! Basic without display

L model features: • •

Twelve digital inputs, eight digital outputs Four additional inputs and outputs on the AS-i modules

The maximum possible options for every model version are as follows: • • • • • • • •

16 Timers 24 Counters Eight Time Switches Three Operating Hour Counters 42 Current Impulse Relays 42 Latching Relays Four Markers for Program Continuation 56 Total Function Blocks

Review 8 1.

___________ is the total number of different circuits each pole controls.

2.

___________ describes the number of isolated circuits that can pass through a relay at one time.

3.

An SPDT relay has ___________ pole(s) and ____________ closed contact position(s).

4.

A timing relay that has received a signal to turn on, and then delays a predetermined amount of time before an action takes place is referred to as ____________ delay.

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Review Answers

Review 1

1) manually; 2) a; 3) b; 4) b; 5) c.

Review 2

1) left to right; 2) A - Node, B - Power Circuit, C - Power Load, D- Control Circuit; E - Control Device; F - Control Load.

Review 3

1) a; 2) excess; 3) overload; 4) a; 5) bimetal.

Review 4

1) 2; 2) LVP; 3) 10, 5; 4) 20; 5) motor starter.

Review 5

1) NEMA, IEC; 2) 5; 3) AC3; 4) 4; 5) 3; 6) 50; 7) 3UA66.

Review 6

1) Consequent-pole motor; 2) progressive control; 3) reducedvoltage starting; 4) Autotransformer.

Review 7

1) pilot device; 2) Three-Wire Control, Two-Wire Control; 3) visual; 4) red, green.

Review 8

1) Throw; 2) Pole; 3) one, two; 4) ON.

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Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. After completing the test, mail in the answer sheet for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. Questions

1.

The standard method of showing a contact is by indicating the circuit condition it produces when the actuating device is in the ____________ state. a. c.

2.

4.

normally open deenergized

green amber

b. d.

red white

Which of the following symbols represents a normally closed, timed open (NCTO) contact? a.

b.

c.

d.

With an increase of current, temperature will ____________ . a. c.

5.

b. d.

A motor that is running would usually be indicated by a ____________ pilot light. a. c.

3.

normally closed energized

decrease remain the same

b. d.

increase increase and decrease

The two circuits involved in the operation of a contactor are the ____________ circuits. a. b. c. d.

power and control power and armature control and electromagnetic control and starter 97

6.

A motor starter is a combination of a/an ____________ . a. b. c. d.

7.

Which of the following is not part of a contactor? a. b. c. d.

8.

b. d.

compelling consequent pole

NEMA ICS

b. d.

UL IEC

The proper overload relay for a World Series 3TF50 contactor is ____________ . a. c.

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selective progressive

The organization primarily concerned with the rating of contactors and starters used in many countries, including the U.S. is ____________ . a. c.

11.

apply torque gradually increase starting torque get motor to full speed faster run the motor at a lower speed

A type of speed selection control that requires the operator to manually increment through each speed step to get to the desired speed is ____________ control. a. c.

10.

armature electromagnetic coil overcurrent sensing device stationary contacts

One reason reduced-voltage starting may be used to start a motor is to ____________ . a. b. c. d.

9.

electromagnet and armature contactor and electromagnet contactor and overload relay overload relay and instantaneous contacts

3UA50 3UA58

b. d.

3UA54 3UA60

12.

A device used to provide visual information of the circuit’s operating condition is a ____________ . a. c.

13.

DPDT SPDT

cut-out pressure pressure range

b. d.

cut-in pressure pressure differential

200 810

b. d.

540 1600

siren buzzer

b. d.

buzzer and siren horn

Furnas INNOVA PLUS™ starters are available up to ____________ HP. a. c.

18.

b. d.

Audible elements for the 8WD42 siganlling column include a ____________ . a. c.

17.

DPST SPST

A NEMA Size 6 starter has a continuous amp rating of ____________ amps. a. c.

16.

selector switch pilot light

The point at which fluid pressure on the diaphragm of a pressure switch causes the contacts to open is referred to as ____________ . a. c.

15.

b. d.

A relay that has two isolated circuits and one closed contact position per pole is a ____________ . a. c.

14.

pushbutton proximity switch

25 100

b. d.

50 250

SIRIUS Type 3R motor starters are available for loads up to ___________ amps. a. c.

95 200

b. d.

135 270

99

19.

In the following diagram, the motor will stop when ____________ . a. b. c. d.

20.

The __________ overload relay integrates with PROFIBUS-DP. a. c.

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the “Stop” button is depressed limit switch “LS1” opens the motor overload contact opens all of the above

3RB10 3UF5

b. d.

ESP 100 3RU11

Table of Contents

Introduction ............................................................................. 2 Totally Integrated Automation and DC Drives ......................... 4 Mechanical Basics ................................................................... 6 DC Motors ............................................................................. 13 Basic DC Motor Operation .................................................... 17 Types of DC Motors .............................................................. 22 DC Motor Ratings .................................................................. 26 Speed/Torque Relationships of Shunt Connected Motors .... 30 Basic DC Drives ..................................................................... 35 Converting AC to DC ............................................................. 39 Basic Drive Operation ............................................................ 44 SIMOREG 6RA70 DC MASTER Electronics .......................... 54 Parameters and Function Blocks ........................................... 69 Engineering Tools................................................................... 75 Applications ........................................................................... 77 Application Examples ............................................................ 78 Selecting a Siemens DC Drive .............................................. 81 Review Answers .................................................................... 85 Final Exam ............................................................................. 86

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Basics of DC Drives and related products. Upon completion of Basics of DC Drives you will be able to: Explain the concepts of force, inertia, speed, and torque

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•

Explain the difference between work and power

•

Describe the operation of a DC motor

•

Identify types of DC motors by their windings

•

Identify nameplate information on a DC motor necessary for application to a DC drive

•

Identify the differences between a power module and a base drive

•

Explain the process of converting AC to DC using thyristors

•

Describe the basic construction of a DC drive

•

Explain the significant differences between 1- and 4quadrant operation in a DC drive

•

Describe features and operation of the Siemens 6RA70 DC MASTER

•

Describe the characteristics of constant torque, constant horsepower, and variable torque applications

This knowledge will help you better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. SIMOREG, SIMOREG DC-MASTER, SIMOVIS, and SIMOLINK are registered trademarks of Siemens Energy & Automation, Inc. Other trademarks are the property of their respective owners.

3

Totally Integrated Automation and DC Drives

Totally Integrated Automation

4

Totally Integrated Automation (TIA) is a strategy developed by Siemens that emphasizes the seamless integration of automation products. The TIA strategy incorporates a wide variety of automation products such as programmable controllers, computer numerical controls, Human Machine Interfaces (HMI), and DC drives which are easily connected via open protocol networks. An important aspect of TIA is the ability of devices to communicate with each other over various network protocols such as PROFIBUS-DP.

Siemens DC Drives

SIMOREG® is the trade name for Siemens adjustable speed DC Drives. SIMOREG stands for SIemens MOtor REGulator. Siemens DC drives are an important element of the TIA strategy. DC motors were the first practical device to convert electrical energy into mechanical energy. DC motors, coupled with DC drives such as the Siemens SIMOREG 6RA70, have been widely used in industrial drive applications for years, offering very precise control.

Although AC motors and vector-control drives now offer alternatives to DC, there are many applications where DC drives offer advantages in operator friendliness, reliability, cost effectiveness, and performance. We will discuss applications later in the course.

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Mechanical Basics

Before discussing Siemens DC drives it is necessary to understand some of the basic terminology associated with the mechanics of DC drive operation. Many of these terms are familiar to us in some other context. Later in the course we will see how these terms apply to DC drives. Force

In simple terms, a force is a push or a pull. Force may be caused by electromagnetism, gravity, or a combination of physical means. The English unit of measurement for force is pounds (lb).

Net Force

Net force is the vector sum of all forces that act on an object, including friction and gravity. When forces are applied in the same direction they are added. For example, if two 10 lb forces were applied in the same direction the net force would be 20 lb.

If 10 lb of force were applied in one direction and 5 lb of force applied in the opposite direction, the net force would be 5 lb and the object would move in the direction of the greater force.

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If 10 lb of force were applied equally in both directions, the net force would be zero and the object would not move.

Torque

Torque is a twisting or turning force that tends to cause an object to rotate. A force applied to the end of a lever, for example, causes a turning effect or torque at the pivot point. Torque (τ) is the product of force and radius (lever distance). Torque (τ) = Force x Radius In the English system torque is measured in pound-feet (lb-ft) or pound-inches (lb-in). If 10 lbs of force were applied to a lever 1 foot long, for example, there would be 10 lb-ft of torque.

An increase in force or radius would result in a corresponding increase in torque. Increasing the radius to 2 feet, for example, results in 20 lb-ft of torque.

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Speed

An object in motion travels a given distance in a given time. Speed is the ratio of the distance traveled to the time it takes to travel the distance.

Linear Speed

The linear speed of an object is a measure of how long it takes the object to get from point A to point B. Linear speed is usually given in a form such as feet per second (f/s). For example, if the distance between point A and point B were 10 feet, and it took 2 seconds to travel the distance, the speed would be 5 f/s.

Angular (Rotational) Speed

The angular speed of a rotating object is a measurement of how long it takes a given point on the object to make one complete revolution from its starting point. Angular speed is generally given in revolutions per minute (RPM). An object that makes ten complete revolutions in one minute, for example, has a speed of 10 RPM.

Acceleration

An object can change speed. An increase in speed is called acceleration. Acceleration occurs when there is a change in the force acting upon the object. An object can also change from a higher to a lower speed. This is known as deceleration (negative acceleration). A rotating object, for example, can accelerate from 10 RPM to 20 RPM, or decelerate from 20 RPM to 10 RPM.

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Law of Inertia

Mechanical systems are subject to the law of inertia. The law of inertia states that an object will tend to remain in its current state of rest or motion unless acted upon by an external force. This property of resistance to acceleration/deceleration is referred to as the moment of inertia. The English system of 2 measurement is pound-feet squared (lb-ft ). If we look at a continuous roll of paper, as it unwinds, we know that when the roll is stopped, it would take a certain amount of force to overcome the inertia of the roll to get it rolling. The force required to overcome this inertia can come from a source of energy such as a motor. Once rolling, the paper will continue unwinding until another force acts on it to bring it to a stop.

Friction

A large amount of force is applied to overcome the inertia of the system at rest to start it moving. Because friction removes energy from a mechanical system, a continual force must be applied to keep an object in motion. The law of inertia is still valid, however, since the force applied is needed only to compensate for the energy lost. Once the system is in motion, only the energy required to compensate for various losses need be applied to keep it in motion. In the previous illustration, for example: these losses include: • • •

Friction within motor and driven equipment bearings Windage losses in the motor and driven equipment Friction between material on winder and rollers

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Work

Whenever a force of any kind causes motion, work is accomplished. For example, work is accomplished when an object on a conveyor is moved from one point to another.

Work is defined by the product of the net force (F) applied and the distance (d) moved. If twice the force is applied, twice the work is done. If an object moves twice the distance, twice the work is done. W=Fxd

Power

Power is the rate of doing work, or work divided by time.

In other words, power is the amount of work it takes to move the package from one point to another point, divided by the time.

10

Horsepower

Power can be expressed in foot-pounds per second, but is often expressed in horsepower (HP). This unit was defined in the 18th century by James Watt. Watt sold steam engines and was asked how many horses one steam engine would replace. He had horses walk around a wheel that would lift a weight. He found that each horse would average about 550 foot-pounds of work per second. One horsepower is equivalent to 500 foot-pounds per second or 33,000 foot-pounds per minute.

The following formula can be used to calculate horsepower when torque (lb-ft) and speed (RPM) are known. It can be seen from the formula that an increase of torque, speed, or both will cause a corresponding increase in horsepower.

Power in an electrical circuit is measured in watts (W) or kilowatts (kW). Variable speed drives and motors manufactured in the United States are generally rated in horsepower (HP); however, it is becoming common practice to rate equipment using the International System of Units (SI units) of watts and kilowatts.

11

Review 1 1.

____________ is the trade name for Siemens motor generators (DC drives).

2.

If 20 lb of force where applied in one direction and 5 lb of force applied in the opposite direction, the net force would be ____________ lb.

3.

If 5 lb of force were applied to a radius of 3 feet, the torque would be ____________ lb-ft.

4.

Speed is determined by ___________ . a. dividing Time by Distance b. dividing Distance by Time c. multiplying Distance x Time d. subtracting Distance from Time

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5.

Work is accomplished whenever ____________ causes motion.

6.

The law of inertia states that an object will tend to remain in its current state of rest or motion unless acted upon by an ____________ ____________ .

DC Motors

DC motors have been used in industrial applications for years. Coupled with a DC drive, DC motors provide very precise control. DC motors can be used with conveyors, elevators, extruders, marine applications, material handling, paper, plastics, rubber, steel, and textile applications to name a few.

13

Construction

DC motors are made up of several major components which include the following: • Frame • Shaft • Bearings • Main Field Windings (Stator) • Armature (Rotor) • Commutator • Brush Assembly Of these components, it is important to understand the electrical characteristics of the main field windings, known as the stator, and the rotating windings, known as the armature. An understanding of these two components will help with the understanding of various functions of a DC Drive.

14

Basic Construction

The relationship of the electrical components of a DC motor is shown in the following illustration. Field windings are mounted on pole pieces to form electromagnets. In smaller DC motors the field may be a permanent magnet. However, in larger DC fields the field is typically an electromagnet. Field windings and pole pieces are bolted to the frame. The armature is inserted between the field windings. The armature is supported by bearings and end brackets (not shown). Carbon brushes are held against the commutator.

Armature

The armature rotates between the poles of the field windings. The armature is made up of a shaft, core, armature windings, and a commutator. The armature windings are usually form wound and then placed in slots in the core.

15

Brushes

16

Brushes ride on the side of the commutator to provide supply voltage to the motor. The DC motor is mechanically complex which can cause problems for them in certain adverse environments. Dirt on the commutator, for example, can inhibit supply voltage from reaching the armature. A certain amount of care is required when using DC motors in certain industrial applications. Corrosives can damage the commutator. In addition, the action of the carbon brush against the commutator causes sparks which may be problematic in hazardous environments.

Basic DC Motor Operation

Magnetic Fields

You will recall from the previous section that there are two electrical elements of a DC motor, the field windings and the armature. The armature windings are made up of current carrying conductors that terminate at a commutator. DC voltage is applied to the armature windings through carbon brushes which ride on the commutator. In small DC motors, permanent magnets can be used for the stator. However, in large motors used in industrial applications the stator is an electromagnet. When voltage is applied to stator windings an electromagnet with north and south poles is established. The resultant magnetic field is static (nonrotational). For simplicity of explanation, the stator will be represented by permanent magnets in the following illustrations.

17

Magnetic Fields

A DC motor rotates as a result of two magnetic fields interacting with each other. The first field is the main field that exists in the stator windings. The second field exists in the armature. Whenever current flows through a conductor a magnetic field is generated around the conductor.

Right-Hand Rule for Motors

A relationship, known as the right-hand rule for motors, exists between the main field, the field around a conductor, and the direction the conductor tends to move. If the thumb, index finger, and third finger are held at right angles to each other and placed as shown in the following illustration so that the index finger points in the direction of the main field flux and the third finger points in the direction of electron flow in the conductor, the thumb will indicate direction of conductor motion. As can be seen from the following illustration, conductors on the left side tend to be pushed up. Conductors on the right side tend to be pushed down. This results in a motor that is rotating in a clockwise direction. You will see later that the amount of force acting on the conductor to produce rotation is directly proportional to the field strength and the amount of current flowing in the conductor.

18

CEMF

Whenever a conductor cuts through lines of flux a voltage is induced in the conductor. In a DC motor the armature conductors cut through the lines of flux of the main field. The voltage induced into the armature conductors is always in opposition to the applied DC voltage. Since the voltage induced into the conductor is in opposition to the applied voltage it is known as CEMF (counter electromotive force). CEMF reduces the applied armature voltage.

The amount of induced CEMF depends on many factors such as the number of turns in the coils, flux density, and the speed which the flux lines are cut. Armature Field

An armature, as we have learned, is made up of many coils and conductors. The magnetic fields of these conductors combine to form a resultant armature field with a north and south pole. The north pole of the armature is attracted to the south pole of the main field. The south pole of the armature is attracted to the north pole of the main field. This attraction exerts a continuous torque on the armature. Even though the armature is continuously moving, the resultant field appears to be fixed. This is due to commutation, which will be discussed next.

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Commutation

In the following illustration of a DC motor only one armature conductor is shown. Half of the conductor has been shaded black, the other half white. The conductor is connected to two segments of the commutator. In position 1 the black half of the conductor is in contact with the negative side of the DC applied voltage. Current flows away from the commutator on the black half of the conductor and returns to the positive side, flowing towards the commutator on the white half.

In position 2 the conductor has rotated 90°. At this position the conductor is lined up with the main field. This conductor is no longer cutting main field magnetic lines of flux; therefore, no voltage is being induced into the conductor. Only applied voltage is present. The conductor coil is short-circuited by the brush spanning the two adjacent commutator segments. This allows current to reverse as the black commutator segment makes contact with the positive side of the applied DC voltage and the white commutator segment makes contact with the negative side of the applied DC voltage.

20

As the conductor continues to rotate from position 2 to position 3 current flows away from the commutator in the white half and toward the commutator in the black half. Current has reversed direction in the conductor. This is known as commutation.

21

Types of DC Motors

The field of DC motors can be a permanent magnet, or electromagnets connected in series, shunt, or compound. Permanent Magnet Motors

The permanent magnet motor uses a magnet to supply field flux. Permanent magnet DC motors have excellent starting torque capability with good speed regulation. A disadvantage of permanent magnet DC motors is they are limited to the amount of load they can drive. These motors can be found on low horsepower applications. Another disadvantage is that torque is usually limited to 150% of rated torque to prevent demagnetization of the permanent magnets.

Series Motors

In a series DC motor the field is connected in series with the armature. The field is wound with a few turns of large wire because it must carry the full armature current. A characteristic of series motors is the motor develops a large amount of starting torque. However, speed varies widely between no load and full load. Series motors cannot be used where a constant speed is required under varying loads. Additionally, the speed of a series motor with no load increases to the point where the motor can become damaged. Some load must always be connected to a series-connected motor. Series-connected motors generally are not suitable for use on most variable speed drive applications.

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Shunt Motors

In a shunt motor the field is connected in parallel (shunt) with the armature windings. The shunt-connected motor offers good speed regulation. The field winding can be separately excited or connected to the same source as the armature. An advantage to a separately excited shunt field is the ability of a variable speed drive to provide independent control of the armature and field. The shunt-connected motor offers simplified control for reversing. This is especially beneficial in regenerative drives.

Compound Motors

Compound motors have a field connected in series with the armature and a separately excited shunt field. The series field provides better starting torque and the shunt field provides better speed regulation. However, the series field can cause control problems in variable speed drive applications and is generally not used in four quadrant drives.

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Speed/Torque Curves

The following chart compares speed/torque characteristics of DC motors. At the point of equilibrium, the torque produced by the motor is equal to the amount of torque required to turn the load at a constant speed. At lower speeds, such as might happen when load is added, motor torque is higher than load torque and the motor will accelerate back to the point of equilibrium. At speeds above the point of equilibrium, such as might happen when load is removed, the motor’s driving torque is less than required load torque and the motor will decelerate back to the point of equilibrium.

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Review 2 1.

The field in larger DC motors is typically an ____________ .

2.

Whenever ____________ flows through a conductor a magnetic field is generated around the conductor.

3.

Voltage induced into the conductors of an armature that is in opposition to the applied voltage is known as ____________ .

4.

Identify the following motor types.

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DC Motor Ratings

The nameplate of a DC motor provides important information necessary for correctly applying a DC motor with a DC drive. The following specifications are generally indicated on the nameplate: • • • • • • • • • •

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Manufacturer’s Type and Frame Designation Horsepower at Base Speed Maximum Ambient Temperature Insulation Class Base Speed at Rated Load Rated Armature Voltage Rated Field Voltage Armature Rated Load Current Winding Type (Shunt, Series, Compound, Permanent Magnet) Enclosure

HP

Horsepower is a unit of power, which is an indication of the rate at which work is done. The horsepower rating of a motor refers to the horsepower at base speed. It can be seen from the following formula that a decrease in speed (RPM) results in a proportional decrease in horsepower (HP).

Armature Speed, Volts, and Amps

Typically armature voltage in the U.S. is either 250 VDC or 500 VDC. The speed of an unloaded motor can generally be predicted for any armature voltage. For example, an unloaded motor might run at 1200 RPM at 500 volts. The same motor would run at approximately 600 RPM at 250 volts.

The base speed listed on a motor’s nameplate, however, is an indication of how fast the motor will turn with rated armature voltage and rated load (amps) at rated flux (Φ). The maximum speed of a motor may also be listed on the nameplate. This is an indication of the maximum mechanical speed a motor should be run in field weakening. If a maximum speed is not listed the vendor should be contacted prior to running a motor over the base speed.

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Winding

The type of field winding is also listed on the nameplate. Shunt winding is typically used on DC Drives.

Field Volts and Amps

Shunt fields are typically wound for 150 VDC or 300 VDC. Our sample motor has a winding that can be connected to either 150 VDC or 300 VDC.

Field Economizing

In many applications it may be necessary to apply voltage to the shunt field during periods when the motor is stationary and the armature circuit is not energized. Full shunt voltage applied to a stationary motor will generate excessive heat which will eventually burn up the shunt windings. Field economizing is a technique used by DC drives, such as the SIMOREG® 6RA70, to reduce the amount of applied field voltage to a lower level when the armature is de-energized (standby). Field voltage is reduced to approximately 10% of rated value. A benefit of field economizing over shuting the field off is the prevention of condensation.

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Insulation Class

The National Electrical Manufacturers Association (NEMA) has established insulation classes to meet motor temperature requirements found in different operating environments. The insulation classes are A, B, F, and H. Before a motor is started the windings are at the temperature of the surrounding air. This is known as ambient temperature. NEMA has standardized on an ambient temperature of 40°C (104°F) for all classes.

Temperature will rise in the motor as soon as it is started. The combination of ambient temperature and allowed temperature rise equals the maximum winding temperature in a motor. A motor with Class F (commonly used) insulation, for example, has a maximum temperature rise of 105°C. The maximum winding temperature is 145°C (40°C ambient + 105°C rise). A margin is allowed to provide for a point at the center of the motor’s windings where the temperature is higher. This is referred to as the motor’s hot spot.

The operating temperature of a motor is important to efficient operation and long life. Operating a motor above the limits of the insulation class reduces the motor’s life expectancy. A 10°C increase in the operating temperature can decrease the life expectancy of a motor by as much as 50%. In addition, excess heat increases brush wear. 29

Speed/Torque Relationships of Shunt Connected Motors

An understanding of certain relationships within a DC motor will help us understand the purposes of various functions in a DC drive later in the course. The formulas given in the following discussion apply to all three types of DC motors (series, shunt, and compound). However, because shunt connected motors are more commonly used with DC drives focus will be on shunt connected DC motors. DC Motor Equations

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In a DC drive voltage applied (Va) to the armature circuit is received from a variable DC source. Voltage applied to the field circuit (Vf) is from a separate source. The armature of all DC motors contains some amount of resistance (Ra). When voltage is applied (Va), current (Ia) flows through the armature. You will recall from earlier discussion that current flowing through the armature conductors generates a magnetic field. This field interacts with the shunt field (Φ) and rotation results.

Armature Voltage

The following armature voltage equation will be used to demonstrate various operating principles of a DC motor. Variations of this equation can be used to demonstrate how armature voltage, CEMF, torque, and motor speed interact with each other. Va = (KtΦn) + (IaRa) Where: Va = Applied Armature Voltage Kt = Motor Design Constants Φ = Shunt Field Flux n = Armature Speed Ia = Armature Current Ra = Armature Resistance

CEMF

We have already learned that rotation of the armature through the shunt field induces a voltage in the armature (Ea) that is in opposition to the armature voltage (Va). This is counter electromotive force (CEMF). CEMF is dependent on armature speed (n) and shunt field (Φ) strength. An increase in armature speed (n) or an increase of shunt field (Φ) strength will cause a corresponding increase in CEMF (Ea). Ea = KtΦn or Ea = Va - (IaRa)

Motor Speed

The relationship between VA and speed is linear as long as flux (Φ) remains constant. For example, speed will be 50% of base speed with 50% of VA applied.

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Motor Torque

The interaction of the shunt and armature field flux produces torque (M). An increase in armature current (Ia) increases armature flux, thereby increasing torque. An increase in field current (If) increases shunt field flux (Φ), thereby increasing torque. M ≈ IaΦ

Constant Torque

Base speed corresponds to full armature voltage (Va) and full flux (Φ). A DC motor can operate at rated torque (M) at any speed up to base speed, by selecting the appropriate value of armature voltage. This is often referred to as the constant torque region. Actual torque (M) produced, however, is determined by the demand of the load (Ia).

Constant Horsepower

Some applications require the motor to be operated above base speed. Armature voltage (Va), however, cannot be higher than rated nameplate voltage. Another method of increasing speed is to weaken the field (Φ). Weakening the field reduces the amount of torque (M) a motor can produce. Applications that operate with field weakening must require less torque at higher speeds.

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Horsepower is said to be constant because speed (N) increases and torque (M) decreases in proportion.

Field Saturation

It can be seen from the speed (n) and torque (M) formulas that field flux (Φ) density has a direct effect on motor speed and available torque. An increase in field flux (Φ), for example, will cause a decrease in speed (n) and an increase in available motor torque (M).

The relationship between field current (If) and flux (Φ) is not as directly proportional as it may appear. As flux density increases the field’s ability to hold additional flux decreases. It becomes increasingly difficult to increase flux density. This is known as saturation. A saturation curve, such as the example shown below, can be plotted for a DC motor. Flux (Φ) will rise somewhat proportionally with an increase of field current (If) until the knee of the curve. Further increases of field current (If) will result in a less proportional flux (Φ) increase. Once the field is saturated no additional flux (Φ) will be developed.

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Review 3 1.

One way to increase motor speed is to ____________ armature voltage. a. increase b. decrease

2.

CEMF is zero when the armature is ____________ . a. turning at low speed b. turning at max speed c. not turning d. accelerating

3.

A ____________ - connected motor is typically used with DC drives.

4.

A DC motor, operating from zero to base speed, can be said to be operating in the constant ____________ range. a. horsepower b. torque

5.

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No additional ____________ can be developed once the field becomes saturated.

Basic DC Drives

The remainder of this course will focus on applying the SIMOREG DC MASTER® 6RA70, to DC motors and associated applications. The SIMOREG DC MASTER 6RA70 drives are designed to provide precise DC motor speed control over a wide range of machine parameters and load conditions. Selection and ordering information, as well as engineering information can be found in the SIMOREG 6RA70 DC MASTER catalog, available from you local Siemens sales representative.

SIMOREG drives are designed for connection to a three-phase AC supply. They, in turn, supply the armature and field of variable-speed DC motors. SIMOREG drives can be selected for connection to 230, 400, 460, 575, 690, and 830 VAC, making them suitable for global use.

35

Siemens SIMOREG DC MASTER 6RA70 drives are available up to 1000 HP at 500 VDC in standard model drives. In addition, drives can be paralleled, extending the range up to 6000 HP. Siemens SIMOREG drives have a wide range of microprocessor-controlled internal parameters to control DC motor operation. It is beyond the scope of this course to cover all of the parameters in detail, however; many concepts common to most applications and drives will be covered later in the course.

36

Power Modules

The SIMOREG 6RA70 is available in a power module and base drive panels. The power module contains the control electronics and power components necessary to control drive operation and the associated DC motor.

Base Drive Panels

The base drive panel consists of the power module mounted on a base panel with line fuses, control transformer, and contactor. This design allows for easy mounting and connection of power cables.

37

High Horsepower Designs

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High horsepower designs are also available with ratings up to 14,000 amps. These drives have input ratings up to 700 VAC and can operate motors with armature ratings up to 750 VDC. For additional information on high horsepower design SIMOREG 6RA70 DC MASTER drives, contact your Siemens sales representative.

Converting AC to DC

Thyristor

A primary function of a DC drive, such as the SIMOREG 6RA70 DC MASTER, is to convert AC voltage into a variable DC voltage. It is necessary to vary to DC voltage in order to control the speed of a DC motor. A thyristor is one type of device commonly used to convert AC to DC. A thyristor consists of an anode, cathode, and a gate.

Gate Current

A thyristor acts as a switch. Initially, a thyristor will conduct (switch on) when the anode is positive with respect to the cathode and a positive gate current is present. The amount of gate current required to switch on a thyristor varies. Smaller devices require only a few milliamps; however, larger devices such as required in the motor circuit of a DC drive may require several hundred milliamps.

Holding Current

Holding current refers to the amount of current flowing from anode to cathode to keep the thyristor turned on. The gate current may be removed once the thyristor has switched on. The thyristor will continue to conduct as long as the anode remains sufficiently positive with respect to the cathode to allow sufficient holding current to flow. Like gate current, the amount of holding current varies from device to device. Smaller devices may require only a few milliamps and larger devices may require a few hundred milliamps.

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The thyristor will switch off when the anode is no longer positive with respect to the cathode.

AC to DC Conversion

The thyristor provides a convenient method of converting AC voltage to a variable DC voltage for use in controlling the speed of a DC motor. In this example the gate is momentarily applied when AC input voltage is at the top of the sinewave. The thyristor will conduct until the input’s sinewave crosses zero. At this point the anode is no longer positive with respect to the cathode and the thyristor shuts off. The result is a half-wave rectified DC.

The amount of rectified DC voltage can be controlled by timing the input to the gate. Applying current on the gate at the beginning of the sinewave results in a higher average voltage applied to the motor. Applying current on the gate later in the sinewave results in a lower average voltage applied to the motor.

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DC Drive Converter

The output of one thyristor is not smooth enough to control the voltage of industrial motors. Six thyristors are connected together to make a 3Ø bridge rectifier.

Gating Angle

As we have learned, the gating angle of a thyristor in relationship to the AC supply voltage, determines how much rectified DC voltage is available. However, the negative and positive value of the AC sine wave must be considered when working with a fully-controlled 3Ø rectifier. A simple formula can be used to calculate the amount of rectified DC voltage in a 3Ø bridge. Converted DC voltage (VDC) is equal to 1.35 times the RMS value of input voltage (VRMS) times the cosine of the phase angle (cosα). VDC = 1.35 x VRMS x cosα The value of DC voltage that can be obtained from a 460 VAC input is -621 VDC to +621 VDC. The following table shows sample values of rectified DC voltage available from 0° to 180°. It is important to note that voltage applied to the armature should not exceed the rated value of the DC motor.

Volts RMS 460 VAC 460 VAC 460 VAC 460 VAC 460 VAC 460 VAC 460 VAC

α 0 30 60 90 120 150 180

Cosine 1.00 0.87 0.50 0.00 -0.50 -0.87 -1.00

Formula VDC = 460 x 1.35 x 1 VDC = 460 x 1.35 x 0.87 VDC = 460 x 1.35 x 0.50 VDC = 460 x 1.35 x 0 VDC = 460 x 1.35 x (-0.50) VDC = 460 x 1.35 x (-0.87) VDC = 460 x 1.35 x (- 1)

VDC 621 538 310.5 0 -310.5 -538 -621

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The following illustration approximates the output waveform of a fully controlled thyristor bridge rectifier for 0°, 60°, and 90°. The DC value is indicated by the heavy horizontal line. It is important to note that when thyristors are gated at 90° the DC voltage is equal to zero. This is because thyristors conduct for the same amount of time in the positive and negative bridge. The net result is 0 VDC. DC voltage will increase in the negative direction as the gating angle (α) is increased from 90° to a maximum of 180°.

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Review 4 1.

An increase of torque causes a corresponding ____________ in horsepower a. increase b. decrease

2.

Typically, DC motor armature voltage is either rated for ____________ VDC or ____________ VDC.

3.

Identify the following insulation classes.

4.

The SIMOREG 6RA70 DC MASTER ____________ drive consists of the power module mounted on a panel with line fuses, control transformer, and a contactor.

5.

A thyristor is one type of device commonly used to convert ____________ . a. DC to AC b. AC to DC

6.

The approximate converted DC voltage of a six-pulse converter when the thyristors are gated at 30° is ____________ VDC.

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Basic Drive Operation

Controlling a DC Motor

A thyristor bridge is a technique commonly used to control the speed of a DC motor by varying the DC voltage. Examples of how a DC rectifier bridge operates are given on the next few pages. Voltage values given in these examples are used for explanation only. The actual values for a given load, speed, and motor vary.

It is important to note that the voltage applied to a DC motor be no greater than the rated nameplate. Armature windings are commonly wound for 500 VDC. The control logic in the drive must be adjusted to limit available DC voltage to 0 - 500 VDC. Likewise, the shunt field must be limited to the motor’s nameplate value.

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Basic Operation

A DC drive supplies voltage to the motor to operate at a desired speed. The motor draws current from this power source in proportion to the torque (load) applied to the motor shaft.

100% Speed, 0% Load

In this example an unloaded motor connected to a DC drive is being operated at 100% speed. The amount of armature current (Ia) and unloaded motor needs to operate is negligible. For the purpose of explanation a value of 0 amps is used. The DC drive will supply only the voltage required to operate the motor at 100% speed. We have already learned the amount of voltage is controlled by the gating angle (COSα) of the thyristors. In this example 450 VDC is sufficient. The motor accelerates until CEMF reaches a value of Va - IaRa. Remember that Va = IaRa + CEMF. In this example IaRa is 0, therefore CEMF will be approximately 450 VDC.

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100% Speed, 100% Load

A fully loaded motor requires 100% of rated armature current at 100% speed. Current flowing through the armature circuit will cause a voltage drop across the armature resistance (Ra). Full voltage (500 VDC) must be applied to a fully loaded motor to operate at 100% speed. To accomplish this, thyristors are gated earlier in the sine wave (36.37°). The DC drive will supply the voltage required to operate the motor at 100% speed. The motor accelerates until CEMF reaches a value of Va - IaRa. Remember that Va = IaRa + CEMF. In this example armature current (Ia) is 100% and Ra will drop some amount of voltage. If we assume that current and resistance is such that Ra drops 50 VDC, CEMF will be 450 VDC.

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1 Quad, 4 Quad

Up to this point we have only looked at a drive in singlequadrant operation. A single-quadrant DC drive will have six thyristors. In the speed-torque chart there are four quadrants of operation according to direction of rotation and direction of torque. A four-quadrant DC drive will have twelve thyristors.

Single-Quadrant Operation

Single-quadrant drives only operate in quadrant I. Motor torque (M) is developed in the forward or clockwise (CW) direction to drive the motor at the desired speed (N). This is similar to driving a car forward on a flat surface from standstill to a desired speed. It takes more forward or motoring torque to accelerate the car from zero to the desired speed. Once the car is at desired speed your foot can be let off the accelerator a little. When the car comes to an incline a little more gas, controlled by the accelerator, maintains speed. To slow or stop a motor in single-quadrant operation the drive lets the motor coast.

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Changing Direction of a DC Motor

There are two ways to change the direction a DC motor rotates. 1. Reverse Armature Polarity 2. Reverse Field Polarity

Reversing in SingleQuadrant Operation

Field contactor reverse kits can be used to provide bidirectional rotation from a single-quadrant drive. To turn the motor in the forward direction the “F” contacts are closed, applying DC voltage in one polarity across the shunt field. Simply reversing the polarity of the field, by opening the “F” contacts and closing the “R” contacts, will reverse direction of a DC motor. It is important to note that field reversal will only work when a quick reversal is not required. The field circuit is inductive and must be brought to 0 current before opening the contacts.

Stopping a Motor

48

Stopping a motor in single-quadrant operation can be done by simply removing voltage to the motor and allowing the motor to coast to a stop. Alternatively, voltage can be reduced gradually until the motor is at a stop. The amount of time required to stop a motor depends on the inertia of the motor and connected load. The more inertia the longer the time.

Dynamic Braking

Dynamic braking is often used on single quadrant drives as a means of stopping a motor quickly. Dynamic braking is not recommended for continuous or repetitive operation. Dynamic braking kits for use with Siemens SIMOREG® drives are typically designed to stop a load operating at base speed a maximum of three consecutive times. After three consecutive stops a waiting period of 15 minutes is required. Dynamic braking develops stopping torque by using a contact (MAUX) to connect a resistor (Rdb) across the armature terminals after the drive controller turns off power to the motor. The field remains energized to supply stopping torque. This is because motor torque (M) depends on armature current (Ia) and field flux (Φ). Armature current (Ia) reverses direction as the motor now acts like a generator. A reversal in armature current (Ia) results in a reversal of torque applied to the motor. Torque, now applied in the opposite direction, acts as a brake to the motor. Stored energy in the rotating motor is applied across the resistor and converted to heat. The resistor is sized to allow 150% current flow initially. Armature voltage decreases as the motor slows down, producing less current through the resistors. The motor is finally stopped due to frictional torque of the connected load.

49

Four-Quadrant Operation

The dynamics of certain loads require four-quadrant operation. If motor voltage is suddenly reduced, negative torque is developed in the motor due to the inertia of the connected load. The motor acts like a generator by converting mechanical power from the shaft into electrical power which is returned to the drive. This is similar to driving a car downhill. The car’s engine will act as a brake. Braking occurs in quadrants II and IV.

Regen

In order for a drive to operate in all four quadrants a means must exist to deal with the electrical energy returned by the motor. Electrical energy returned by the motor tends to drive the DC voltage up, resulting in excess voltage that can cause damage. One method of getting four-quadrant operation from a DC drive is to add a second bridge connected in reverse of the main bridge. The main bridge drives the motor. The second bridge returns excess energy from the motor to the AC line. This process is commonly referred to as regen. This configuration is also referred to as a 4-Quad design.

50

Motoring

The motor receives power from the incoming line. In this example the motor is operating at full speed (500 VDC).

100% Speed, -100% Load

When the motor is required to stop quickly, the motoring bridge shuts off and the regen bridge turns on. Due to the initial inertia of the connected load the motor acts like a generator, converting mechanical power at the shaft into electrical power which is returned to the AC line. The IaRa voltage drop (-50 VDC) is of opposite polarity then when the drive was supplying motoring power. The control logic is gating thyristors in the regen bridge at an angle of 130° and the resultant DC voltage on the bridge is 400 VDC, in the opposite polarity. Because the regen bridge is of opposite polarity, the voltage applied to the motor acts like an electrical brake for the connected load.

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Regen vs. Dynamic Braking

Regen and dynamic braking provide the same amount of braking power to slow a motor from maximum speed in field weakening to base speed. This is because field strength increases until the motor reaches base speed. However, from base speed to stop, regen is capable of slowing a motor at a faster rate. In addition, regen can develop torque at zero speed to bring the motor to a complete stop. Another advantage of regen is that regen braking is not limited in duty cycle and cool-down periods. Applications that require frequent braking or have overhauling loads should consider four quadrant operation with regen braking.

Reversing

52

A four-quadrant drive can easily reverse the direction of rotation of a DC motor simply by applying armature voltage in the opposite polarity. This is accomplished by using what was the regen bridge to motor. The bridge that was used to drive the motor in the forward direction becomes the regen bridge.

Review 5 1.

When torque is developed in the forward direction and the armature is turning in the forward direction, the motor is operating in quadrant ____________ .

2.

When the armature is turning in the forward direction but torque is developed in the reverse direction, the motor is operating in quadrant ____________ .

3.

The direction of rotation of a DC motor, operated from a 6-pulse converter, can be reversed by reversing the polarity of the DC voltage applied to the ____________ field.

4.

____________ ____________ is a method used to stop a motor quickly by applying a resistor to the armature.

5.

Which of the following is an advantage of a 4-quad converter? a. Instead of being dissipated in heat, excess energy is returned to the supply line. b. From base speed to zero speed a 4-quad converter will stop a motor faster than a 1-quad converter. c. A 4-quad converter can reverse motor direction by simply applying voltage in the opposite polarity across the armature. d. all of the above.

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SIMOREG 6RA70 DC MASTER Electronics

Up to this point we have looked at the power components of a DC Drive necessary to control the speed of a DC motor. The actual control of these components is accomplished with electronic hardware and technology software. Speed Control with CEMF Feedback

Speed control is one mode of operation. The drive will attempt to maintain a constant speed regardless of the load’s torque. A speed reference is input into a ramp function generator which applies reference voltage to the speed controller over a specified period of time. This allows a smoother acceleration of the motor and connected load. The output of the speed controller is routed to the firing circuit, which controls the amount of voltage applied to the armature. You will recall that Va (applied voltage) = IaRa + CEMF. IaRa is proportional to load and is generally 10% of nameplate armature voltage at 100% load. Therefore, as load torque/ current varies between 0 and 100%, IaRa varies from 0 to 50 VDC for a 500 VDC armature. Va and Ia are constantly monitored. Ra is measured during the comissioning and tuning of the drive. Because Va, Ia, and Ra are known values, CEMF (Ea) can be precisely calculated. CEMF is proportional to speed and the speed controller uses this value to calculate actual speed. Speed control with CEMF feedback can only be used on applications where the motor operates between zero and base speed. CEMF feedback provides approximately 2-5% speed regulation.

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Speed Control with Tach Feedback

A tachometer can be used when a more accurate measurement of speed is needed, or when the motor will be operated above base speed. A measurement of actual speed is returned to the speed controller. The speed controller will make armature voltage adjustments to maintain constant speed with variations in load. If, for example, load is suddenly increased the motor will slow, reducing speed feedback. The speed controller will output a higher signal to the current controller, which will increase the firing angle of the firing circuit. The resulting increased armature voltage applies more torque to the motor to offset the increased load. Motor speed will increase until it is equal with the speed reference setpoint. When the motor is rotating faster than desired speed armature voltage is reduced. In a four-quad drive DC armature voltage could momentarily be reversed to slow the motor at a faster rate to the desired speed. Several tachs can be used with the SIMOREG 6RA70. DC tachs can provide approximately 0.10 to 2% regulation. Digital (pulse) tachs can provide approximately 0.10 to 0.25% regulation. These values vary depending on the tach and the operating conditions.

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Current Measurement

The drive monitors current, which is summed with the speed control signal at the current controller. The drive acts to maintain current at or below rated current by reducing armature voltage if necessary. This results in a corresponding reduction in speed until the cause of the overcurrent is removed.

Torque Control

Some applications require the motor to operate with a specific torque regardless of speed. The outer loop (speed feedback) is removed and a torque reference is input. The current controller is effectively a torque controller because torque is directly proportional to current.

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Tuning the Drive

A feature of the SIMOREG 6RA70 DC MASTER is the ability to self tune for a given motor and associated load. An improperly tuned control may result in an excessive speed overshoot when changing from one speed to another. Oscillations can occur which contribute to system instability.

A properly tuned drive will have an initial overshoot of approximately 43% and settle into a new speed quickly. This provides a stable system with quick response.

The SIMOREG 6RA70 DC MASTER has three self-tuning routines to match the performance of the drive to the controlled motor and associated load. •

Armature Tuning tunes the drive to the motor characteristics

•

Speed Tuning tunes the drive to the connected load

•

CEMF Tuning tunes the drive for field weakening

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CUD1 Board

The CUD1 board is the main control board for the SIMOREG 6RA70. This board contains the necessary software and hardware interfaces for operating the drive in speed or torque control. It has input and output connections for wiring the control devices of various functions such as start/stop pushbuttons and speed potentiometer. The CUD1 board has comprehensive diagnostics for troubleshooting. CUD1 also contains the necessary software for self-tuning. Programmable binary outputs, used to indicate the condition of the drive, are available on X171. Binary inputs are also available to start and stop the drive on X171. In addition, there are two programmable binary inputs for such functions as reverse and jog. The 6RA70 accepts analog inputs for speed control on X174. Programmable analog outputs on X175 provide meter indication of various drive parameters such as current and voltage. A motor temperature switch can be connected to X174 and is used to stop the drive if the motor becomes overheated. Connections are also available on X173 for a digital tach.

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Typical Connections

The following diagram shows a typical connection used to operate the drive. A normally open (NO) contact is used to start and stop the drive.

Alternately, pushbuttons can be used to start and stop the drive.

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Programming and Operating Sources

SIMOREG 6RA70 drives can be programmed and operated from various sources, such as the PMU, OP1S, or other SIMATIC® HMI device such as the TP170A, TP170B, OP27, or MP370. In addition to these, various methods of serial communication is available through RS232 or RS485 connections. These will be discussed later in this section with the option boards. The PMU can be used alone or with the OP1S. The OP1S can be mounted directly on the PMU or up to 200 meters away with an external power supply. Parameters, such as ramp times, minimum and maximum speed, and modes of operation are easily set. The changeover key (“P”) toggles the display between a parameter number and the value of the parameter. The up and down pushbuttons scroll through parameters and are used to select a parameter value, once the “P” key sets the parameter. The OP1S has a numbered key pad for direct entry.

SIMATIC HMI Devices

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Another, more robust option, is a SIMATIC HMI device such as the TP170A. The TP170A uses a touch-sensitive screen for control and monitoring. It is powered from the drive and standard PROFIBUS connections.

CUD2 Expansion Board

The CUD2 is typically selected when additional inputs and outputs (I/O) are required. CUD2 I/O is selectable. An advantage to the CUD2 expansion board is that it mounts directly on the CUD1 and requires no additional hardware. The CUD2 provides four optically isolated binary inputs, four selectable binary inputs to ground, two analog inputs, one analog input for motor temperature evaluation, two binary outputs, and one serial interface. In addition to the expanded I/O, the CUD2 provides a parallel interface for paralleling up to six power modules.

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EB1 and EB2 Expansion Boards

EB1 and EB2 are half-sized expansion boards that provide a number of additional I/O possibilities. EB1 has three binary inputs and four bidirectional binary I/O. Bidirectional I/O can be configured as a binary input or output. One of the analog inputs is used as a voltage or current reference input. Two of the analog inputs can also be configured as binary inputs. EB2 has two binary inputs, one analog input, one analog output, and four relay contacts. Three of the contacts are normally open (NO) and one of the contacts can be configured as normally open (NO) or normally closed (NC).

T400 Technology Board

I/O Isolated Binary Inputs

CUD2 4

EB1 0

EB2 0

Binary Inputs

4

3

2

Bidirectional Binary I/O

0

4

0

Analog Inputs

2

3

1

Analog Outputs

2

2

1

Relay (Binary) Outputs

2

0

4

Serial Interface

1

0

0

Parallel Converter Interface

1

0

0

The T400 is an option board that is used to provide specialized features for applications, such as winders, tension control, position control, and hoisting gear. In addition to applying built-in technology functions, users familiar with the Siemens PLC software SIMATIC STEP-7 can also implement their own process functions.

To implement the various control functions required by specific applications the T400 has two analog outputs, five analog inputs, two binary outputs, eight binary inputs, four bidirectional binary inputs/outputs, two incremental encoder inputs, and two serial interfaces. 62

Communications

One of the strong points of the SIMOREG 6RA70 is its serial interface capabilities, which makes it easy to integrate the drive with other automation components. Communication options are available for PROFIBUS-DP, SIMOLINK®, CAN, and DeviceNet communications.

SLB

The SLB communication board is used for peer-to-peer communication with other Siemens drives via SIMOLINK. SIMOLINK is a high speed fiber optic ring bus that allows various data to be passed from one drive to the next. Communication is not limited to the SIMOREG 6RA70. SIMOLINK can also communicate between Siemens AC drives such as the MASTERDRIVE MC and MASTERDRIVE VC.

CBP2

PROFIBUS-DP is an open bus standard for a wide range of applications in various manufacturing and automation applications. Siemens DC drives can easily communicate with other control devices such as programmable logic controllers (PLCs) and personal computers (PCs) through the PROFIBUSDP communication system and other various protocols. The CBP2 board is required to communicate via PROFIBUS-DP.

63

CBC

ISO is a federation of standards organizations from over 100 countries that develops voluntary standards for business, science, and technology. The official name is Organization Internationale de Normalisation, also known in the United States as the International Organization for Standardization. The CBC communication board is used to communicate with CAN protocol, which is an ISO standard (ISO 11898) for serial data communications. CAN protocol was initially developed in 1986 for the automotive industry. Today communication with CAN protocol can also be found in other industrial automation applications. One device, such as a PLC or computer, acts as a master. SIMOREG drives equipped with CBC boards and other controllable devices configured for CAN act as slaves. CAN uses a simple twisted pair of wires for transmission of control and parameter value data between SIMOREG drives with CBC boards.

64

CBD

The CBD communication board is used to communicate with DeviceNet. DeviceNet is another communication protocol that was developed based on the CAN technology. DeviceNet provides a low-level network for DeviceNet enabled devices such as sensors, motor starters, and drives to communicate with higher-level devices such as computers and PLCs. DeviceNet can read the state of devices, such as on/off, as well as start and stop motors (motor starters). SIMOREG 6RA70 DC MASTERs equipped with a CBD board can be added to a DeviceNet network. A DeviceNet enabled master device can control the operation, such as start, stop, accel, and decel.

SBP

Digital tachometers (encoders) can be used to measure the actual speed of a motor. The SBP encoder board can be also be used to monitor an external encoder, such as might be connected to the driven machine.

65

Electronics Box

The electronics box contains the CUD1 board (main control board) and option boards. The CUD1 board is plugged into slot 1.

Mounting Option Boards

There are several option boards available, which will be discussed later in this section. Option boards are automatically recognized by the drive. Up to six boards can be installed in the electronics box. A Local Bus Adapter (LBA) is required if mounting positions 2 or 3 are needed. In addition, adapter boards (ADB) are necessary for slots D, E, F, and G when utilizing the half-size option boards.

66

There are a few rules that must be followed when mounting option boards: •

Option boards may be plugged into positions 2 or 3, however, position 2 must be filled first.

•

When used, a technology board (T400) is always installed in position 2.

•

If a communication board (CBP2, CBC. or CBD) is used with a technology board the communication board is placed in slot G.

•

It is unnecessary and not possible to use expansion boards EB1 and EB2 in conjunction with the technology board T400. T400 has its own expanded inputs and outputs (I/O).

•

It is unnecessary and not possible to use the pulse encoder board (SBP) or the SIMOLINK communication board (SLB) in conjunction with T400. T400 has provision to connect an encoder.

•

A maximum of two supplementary boards of the same type may be used in one drive. For example, no more than two communication boards or two expansion boards can be used.

The following chart shows the mounting positions for CUD1 and option boards. Board

LBA

ADB

Location 1

CUD1 CUD2 CBP2 CBC CBD SLB SBP T400 EB1 EB2

No No Yes Yes Yes Yes Yes Yes Yes Yes

No No Yes Yes Yes Yes Yes No Yes Yes

Yes Yes No No No No No No No No

Location 2 D E No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

Location 3 F G No No No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes

67

Review 6 1.

____________ is the designation of the main electronic control board in the SIMOREG 6RA70 DC MASTER.

2.

A ____________ ____________ ____________ is required when mounting option boards in the electronics box.

3.

Position ____________ must be filled first when installing option boards.

4.

____________ tuning tunes a drive to the motor characteristics.

5.

Technology board T400 can be installed in location ____________ .

6.

An advantage of the CUD2 expansion board is that it mounts directly on ____________ and requires no additional hardware.

7.

____________ expansion board has the most bidirectional binary I/O. a. CUD2 b. EB1 c. EB2

8.

____________ is used to communicate with PROFIBUS-DP.

9.

____________ is used to communicate with other Siemens drives via SIMOLINK.

10. A second digital tachometer is connected to the drive through an ____________ board when T400 is not used.

68

Parameters and Function Blocks

The SIMOREG 6RA70 DC MASTER features an extensive parameter set that can easily be adapted to almost any drive task, from simple to complex. A wide scope of parameters include: • • • • • •

Acceleration/Deceleration Control Automatic Restart Function Field Reversal Various Arithmetic and Boolean Logic Operations Technology Controllers Velocity/Speed and Diameter Calculators

In addition, the SIMOREG 6RA70 DC MASTER has extensive status indicators and display parameters for monitoring. The SIMOREG 6RA70 DC MASTER also supports a large database of faults and alarms. This provides the operator with a clear indication of what may be needed to correct the problem. There are numerous parameters within the SIMOREG 6RA70 DC MASTER. It is beyond the scope of this course to cover these in any detail. However, it is important to understand how parameters and function blocks work together. Parameters

Parameter values are used to provide settings to the drive. In the Siemens SIMOREG 6RA70 DC MASTER each parameter is clearly designated by an assigned number. Parameters are differentiated according to their function: • •

Function Parameters (can be read and written) Visualization Parameters (can only be read)

69

Function Parameters

Acceleration or deceleration times are examples of function parameters. A feature of DC drives is the ability to increase or decrease the armature voltage gradually. This accelerates and decelerates the motor smoothly with less stress on the motor and connected load. Parameters P303 and P304 work together to instruct the SIMOREG 6RA70 DC MASTER how much acceleration/ deceleration time is needed from 0 to 100% speed. P303 and P304 can be set to any value between 0.0 to 650 seconds. If P303 were set to 20.00, for example, the drive would take 20 seconds to accelerate the motor from 0 to 100% speed. Acceleration and deceleration time is linear which means the time speed curve can be accurately tracked. The motor would be at 25% speed after 5 seconds and 50% speed after 10 seconds.

Rounding is a feature that can be added to the acceleration/ deceleration curve. This feature smooths the transition between starting and finishing a ramp.

70

Visualization Parameters

Visualization parameters are used for visualizing internal quantities. These parameters are only displayed and cannot be changed by the operator. Visualization parameters are distinguished by a lower case “r” . Parameter r038, for example, displays the value of voltage output to the motor.

Function Blocks

A function block consists of several parameters grouped together to perform a specific task. The following function block represents one example of how a proportional/integral (PI) controller can be used in speed control of a SIMOREG 6RA70 DC MASTER.

Function Parameters

The response of a function block is determined by function parameters. Proportional gain and integral time, for example, determine the response of a PI-controller. Each parameter has a name, identifying number, value range, and a factory setting. Function parameters can be indexed.

71

Indexing and Data Sets

In many applications it may be desirable to configure the SIMOREG 6RA70 DC MASTER for variations in operation. For example, there may be a situation in an application where it is desirable to have different acceleration times. Indexed parameters can have up to four different values stored with them. Each value stored is part of a data set. Parameter P303, acceleration time, is an example of an indexed parameter. P303 can have four different acceleration times stored. P303 could, for example, have the following values: P303.1 = 0.50 P303.2 = 1.00 P303.3 = 3.00 P303.4 = 8.00 If data set 1 is active, the acceleration time is 0.50 seconds. If data set 2 is active, the acceleration time is 1.00 second. Data sets are operator selected and can be changed at any time.

PI-Controller

PI-controllers are commonly used in drive technology. In our example the desired speed and actual speed are input to a summation point. The two signals are opposite in polarity. When the actual speed is equal to the desired speed the deviation, which is input into the PI-controller, is zero (0). Whenever desired speed and actual speed are different there is a deviation. Changes in load on the motor, for example, can affect motor speed. A sudden increase in load would cause the motor to slow down. This would decrease the feedback from actual speed and the deviation would become more positive. It is also possible that the application may require the motor to slow down or speed up. Until the motor reaches the new desired speed there will be a deviation.

72

The PI-controller’s job is to make speed corrections quickly a minimal amount of overshoot and oscillation. Parameter P225 (gain) and parameter P226 (time) are used to tune the PIcontroller’s performance. The end result should be a fast response time with about a 43% initial overshoot. The motor should then settle in to the new desired speed.

Connectors and Binectors

Connectors and binectors are elements used to exchange signals between function blocks. Connectors are used to store analog values. Analog values are stored in the form that is represented by 16 bit or 32 bit words. Binectors are used to store binary (digital) information.

73

Connectors and binectors are identified by a name and number. Connectors with 16 bit resolution are identified with a “K”. Connectors with 32 bit resolution are identified with a “KK” . Binectors are identified with a “B”.

BICO

74

BICO is the term used to describe the method of connecting function blocks together. This is performed with BInectors and COnnectors. A connection between two function blocks consists of a connector or binector and a BICO parameter. With BICO parameters you can determine the sources of the input signals of a function block. This allows the user to “softwire” function blocks to meet specific application requirements.

Engineering Tools

There are several engineering tools available optionally. These tools aid in programming, operating, troubleshooting, and managing SIMOREG 6RA70 DC MASTER drives. SIMOVIS

SIMOVIS® can be used to aid start-up, setting and saving parameters, and as a diagnostic tool for troubleshooting. A feature of SIMOVIS is the graphics display. With this feature oscilloscope functions can be displayed on a computer screen.

75

QuickStart

QuickStart is another tool useful in setting up SIMOREG DC drives. A feature of this tool is the ability to communicate with specific drives in a network of drives. A Wizard driven menu leads operators through a simplified start-up procedure step-bystep.

Drive ES

Drive ES is used to integrate Siemens drives with the SIMATIC automation world. There are three Drive ES packages available.

Package Drive ES Basic

Drive ES Graphic

Description Structured similar to SIMOVIS allowing commissioning, parameter handling, oscilloscope readout, and fault evaluation. Based on STEP 7 for integration into SIMATIC. Provides graphic configuring of BICO function blocks. Requires Drive ES Basic and a SIMATIC programming tool called SIMATIC CFC.

Drive ES SIMATIC Provides function blocks and examples of SIMATIC projects. Requires Drive ES Basic.

76

Applications

When applying a DC drive and motor to an application it is necessary to know the horsepower, torque, and speed characteristics of the load. The following chart shows typical characteristics of various loads.

Loads generally fall into one of three categories:

Category

Description

Constant Torque

The load is essentially the same throughout the speed range. Hoisting gear and belt conveyors are examples.

Variable Torque

The load increases as speed increases. Pumps and fans are examples.

Constant The load decreases as speed increases. Winders Horsepower and rotary cutting machines are examples.

77

Application Examples

The Siemens SIMOREG 6RA70 DC MASTER drives are designed to handle the most challenging applications. The following examples are just some of applications the SIMOREG can be used on. Winders/Coilers

78

DC motors offer superior characteristics at low speed for winder and coiler operation and performance. In winder applications maintaining tension at standstill is a very important operation. DC motors offer a wide speed range at rated torque. On many winder applications that run in an extended speed range a smaller horsepower DC motor could do the same job as a larger horsepower AC motor.

Marine Applications

DC drives offer several advantages in marine applications. Compact sizing is one of the biggest advantages. DC drives also adapt well from generator supplies such as found in the marine industry.

Crane/Hoist

DC offers several advantages in applications that operate at low speed, such as cranes and hoists. Advantages include low speed accuracy, short-time overload capability, size, torque proving control, and load sharing.

79

Mining/Drilling

DC is often preferred in the high horsepower applications required in the mining and drilling industry. DC drives offer advantages in size and cost. They are rugged, dependable, and proven in the industry.

Extruding

Extruding is a price competitive industry. DC offers economical solutions in the 60 to 1000 HP range which is commonly used in extruding applications.

80

Selecting a Siemens DC Drive

The following flow diagram, along with the selection charts, will help you select the right DC drive for your application.

81

The following tables provide catalog numbers for SIMOREG DC drives up to 1000 HP. For larger drives consult your Siemens sales representative. Power Module Single Quad, Non-Regen

82

Horsepower 240 VDC 500 VDC 3 7.5 7.5 15 15 30 25 60 40 75 60 125 75 150 125 250 150 300 250 500 700 1000

Rated Armature (Amps DC) 15 30 60 100 140 210 255 430 510 850 1180 1660

Catalog Number 6RA7018-6FS22-0Z+X01 6RA7025-6FS22-0Z+X01 6RA7028-6FS22-0Z+X01 6RA7031-6FS22-0Z+X01 6RA7075-6FS22-0Z+X01 6RA7078-6FS22-0Z+X01 6RA7082-6FS22-0Z+X01 6RA7085-6FS22-0Z+X01 6RA7087-6FS22-0Z+X01 6RA7091-6FS22-0Z+X01 6RA7093-4GS22-0Z+X01 6RA7095-4GS22-0Z+X01

Power Module Four Quad, Regen

Base Drive Signle Quad, Non-Regen

Base Drive Four Quad, Regen







Catalog Number 6RA7018-6FV62-0Z+X01 6RA7025-6FV62-0Z+X01 6RA7028-6FV62-0Z+X01 6RA7031-6FV62-0Z+X01 6RA7075-6FV62-0Z+X01 6RA7078-6FV62-0Z+X01 6RA7082-6FV62-0Z+X01 6RA7085-6FV62-0Z+X01 6RA7087-6FV62-0Z+X01 6RA7091-6FV62-0Z+X01 6RA7093-4GV62-0Z+X01 6RA7095-4GV62-0Z+X01

Catalog Number 6RA7013-2FS22-0 6RA7018-2FS22-0 6RA7025-2FS22-0 6RA7030-2FS22-0 6RA7072-2FS22-0 6RA7075-2FS22-0 6RA7077-2FS22-0 6RA7082-2FS22-0 6RA7083-2FS22-0 6RA7087-2FS22-0 6RA7091-2FS22-0 6RA7094-2FS22-0

Catalog Number 6RA7013-2FV62-0 6RA7018-2FV62-0 6RA7025-2FV62-0 6RA7030-2FV62-0 6RA7072-2FV62-0 6RA7075-2FV62-0 6RA7077-2FV62-0 6RA7082-2FV62-0 6RA7083-2FV62-0 6RA7087-2FV62-0 6RA7091-2FV62-0 6RA7094-2FV62-0

83

Review 7

84

1.

Parameters that can be read only are referred to as ____________ parameters.

2.

A function block consists of several ____________ grouped together to perform a specific task.

3.

____________ is the term used to describe the method of connecting function blocks together.

4.

Winders are examples of ____________ ____________ applications.

5.

Identify the category of the following speed, torque, and horsepower graphs.

Review Answers

Review 1

1) SIMOREG; 2) 15; 3) 15; 4) b. Dividing Distance by Time; 5) force; 6) external force.

Review 2

1) electromagnet; 2) current; 3) CEMF; 4) a. Permanent Magnet, b. Compound, c. Shunt, d. Series.

Review 3

1) a. increase; 2) c. not turning; 3) shunt; 4) b. torque; 5 flux.

Review 4

1) a. increase; 2) 250 VDC or 500 VDC; 3) a. A, b. B, c. F, d. H; 4) base; 5) b. AC to DC; 6) 538.

Review 5

1) I; 2) II; 3) shunt; 4) Dynamic Braking; 5) d. all of the above.

Review 6

1) CUD1; 2) Local Bus Adapter; 3) 2; 4) Armature; 5) 2; 6) CUD1; 7) b. EB1; 8) CBP2; 9) SLB; 10) SBP.

Review 7

1) visualization; 2) parameters; 3) BICO; 4) constant horsepower; 5) a. Constant Torque, Constant Horsepower, Variable Torque.

85

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. After completing the test, mail the answer sheet in for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. Those receiving a score of less than 70% will be provided a second test. Questions

1.

The type of DC motor best suited for use with DC drives is the ____________ wound motor. a. b. c. d.

2.

____________ is the trade name for Siemens DC drives. a. b.

3.

c. d.

SIMOVIS SIMOLINK

armature voltage CEMF field current (If) armature resistance (Ra)

A decrease in field flux strength (Φ) causes a/an ____________ . a. b. c. d.

86

SIMOREG SIMOVERT

The base speed of a motor is an indication of how fast the motor will turn with rated ____________ and rated load (amps) at rated flux (Φ). a. b. c. d.

4.

series shunt compound series or shunt

decrease in armature voltage increase in armature voltage increase in motor torque decrease in motor torque

5.

____________ is the voltage induced into an armature conductor of a DC motor in opposition to applied voltage. a. b. c. d.

6.

____________ current refers to the minimum amount of current flowing from anode to cathode to keep a thyristor turned on. a. d. c. d.

7.

0 310.5 538 621

A 1-quad drive uses ____________ thyristors to convert AC to a variable voltage DC. a. b.

9.

Armature current Gating current Holding current Field current

The value of rectified DC voltage obtained from a 460 VAC 3Ø source when the thyristors are gated at 60° is ____________ VDC. a. b. c. d.

8.

Armature voltage Field voltage CEMF EMF

4 6

c. d.

8 12

____________ is a method sometimes used on 1-quad drives as a means of stopping a motor quickly by converting mechanical energy to heat. a. b. c. d.

Regen Field reversal Dynamic Braking Armature reversal

87

10.

Which of the following is not an advantage of regen over dynamic braking? a. b. c. d.

11.

____________ tuning tunes the 6RA70 drive to the motor characteristics. a. b.

12.

CUD1 CUD2

c. d.

SLB CBP2

ADB Adapter Board LBA Local Bus Adapter ADB and LBA No additional hardware

D E

c. d.

F G

The command to start the 6RA70 drive is received on ____________ of CUD1. a. b. c. d.

88

CEMF Field

If a communication board (CBP2, CBC, or CBD) is used with a technology board, the communication board must be placed in slot ____________ . a. b.

15.

c. d.

CUD2 requires ____________ to install in the 6RA70. a. b. c. d.

14.

Speed Armature

____________ is the main control board in the 6RA70 which controls drive operation. a. b.

13.

Regen brakes faster from max speed to base speed Regen brakes faster from base speed to stop Regen is not limited to duty cycle and cooldown periods Regen can develop torque at zero speed

Terminal 106 of XS Terminal 4 of X174 Terminal 37 of X171 Terminal 14 of X175

16.

Hoisting gear is an example of a ____________ load. a. b. c. d.

17.

____________ is used to communicate with PROFIBUS-DP. a. b.

18.

c. d.

CBD SBP

SIMATIC SIMOVIS

c. d.

BICO QuickStart

____________ is an example of a visualization parameter. a. b.

20.

CBC CBP2

____________ is the term used to describe the method of connecting function blocks together. a. b.

19.

constant torque variable torque constant horsepower constant speed

P225 r038

c. d.

K165 B0205

The correct catalog number for a SIMOREG 6RA70 DC MASTER, base drive, four quad, to be used with armature amps rated for 100 amps is ____________ . a. b. c. d.

6RA7031-6FS22-0Z+X01 6RA7031-6FV62-0Z+X01 6RA7030-2FS22-0 6RA7030-2FV62-0

89

Notes

90

Notes

91

Notes

92

Table of Contents

Introduction ..............................................................................2 Electron Theory .........................................................................4 Conductors, Insulators and Semiconductors ............................5 Electric Charges ........................................................................7 Current......................................................................................9 Voltage .................................................................................... 11 Resistance .............................................................................. 13 Simple Electric Circuit ............................................................. 15 Ohm’s Law ............................................................................. 16 DC Series Circuit .................................................................... 18 DC Parallel Circuit ...................................................................23 Series-Parallel Circuits ............................................................30 Power......................................................................................34 Magnetism .............................................................................37 Electromagnetism ..................................................................39 Introduction to AC ...................................................................42 AC Generators ........................................................................44 Frequency ...............................................................................47 Voltage and Current ................................................................48 Inductance ..............................................................................51 Capacitance ............................................................................56 Inductive and Capacitive Reactance .......................................61 Series R-L-C Circuit .................................................................67 Parallel R-L-C Circuit ................................................................69 Power and Power Factor in an AC Circuit ................................ 71 Transformers ...........................................................................75 Three-Phase Transformers ......................................................80 Review Answers .....................................................................83 Final Exam ..............................................................................84 1

Introduction

Welcome to the first course in the STEP series, Siemens Technical Education Program designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Basics of Electricity and is designed to prepare you for subsequent courses on Siemens Energy & Automation products. Upon completion of Basics of Electricity you will be able to:

2

•

Explain the difference between conductors and insulators

•

Use Ohm’s Law to calculate current, voltage, and resistance

•

Calculate equivalent resistance for series, parallel, or series-parallel circuits

•

Calculate voltage drop across a resistor

•

Calculate power given other basic values

•

Identify factors that determine the strength and polarity of a current-carrying coil’s magnetic field

•

Determine peak, instantaneous, and effective values of an AC sine wave

•

Identify factors that effect inductive reactance and capacitive reactance in an AC circuit

•

Calculate total impedance of an AC circuit

•

Explain the difference between real power and apparent power in an AC circuit

•

Calculate primary and secondary voltages of single-phase and three-phase transformers

•

Calculate kVA of a transformer

The objectives listed above may sound strange to you. You may also wonder why you would need to know these things to sell Siemens Energy & Automation products. Developing a basic knowledge of electrical concepts, however, will help you to better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts.

3

Electron Theory

Elements of an Atom

All matter is composed of molecules which are made up of a combination of atoms. Atoms have a nucleus with electrons orbiting around it. The nucleus is composed of protons and neutrons (not shown). Most atoms have an equal number of electrons and protons. Electrons have a negative charge (-). Protons have a positive charge (+). Neutrons are neutral. The negative charge of the electrons is balanced by the positive charge of the protons. Electrons are bound in their orbit by the attraction of the protons. These are referred to as bound electrons. Electron Proton Nucleus

Free Electrons

4

Electrons in the outer band can become free of their orbit by the application of some external force such as movement through a magnetic field, friction, or chemical action. These are referred to as free electrons. A free electron leaves a void which can be filled by an electron forced out of orbit from another atom. As free electrons move from one atom to the next an electron flow is produced. This is the basis of electricity.

Conductors, Insulators and Semiconductors

Conductors

An electric current is produced when free electrons move from one atom to the next. Materials that permit many electrons to move freely are called conductors. Copper, silver, aluminum, zinc, brass, and iron are considered good contors. Copper is the most common maal used for contors and is relatively insive.

Insulators

Materials that allow few free electrons are called insulators. Materials such as plastic, rubber, glass, mica, and ceramic are good insulators.

An electric cable is one example of how conductors and insulators are used. Electrons flow along a copper conductor to provide energy to an electric device such as a radio, lamp, or a motor. An insulator around the outside of the copper conductor is provided to keep electrons in the conductor. Rubber Insulator Copper Conductor

5

Semiconductors

Semiconductor materials, such as silicon, can be used to manufacture devices that have characteristics of both conductors and insulators. Many semiconductor devices will act like a conductor when an external force is applied in one direction. When the external force is applied in the opposite direction, the semiconductor device will act like an insulator. This principle is the basis for transitors, diodes, and other solidstate electronic devices.

Transistor

Diode

Review 1 1.

List the three basic elements of an atom and state the charge of each (positive, negative, or neutral). Element

Charge

____________ ____________ ____________ ____________ ____________ ____________ 2.

An electron forced out of orbit by an external force is called a ____________ ____________ .

3.

Conductors allow ____________ free electrons to flow when an external electric force is applied.

4.

Which of the following materials are good conductors? a. copper b. plastic c. silver d. rubber

5.

6

e. f. g. h.

aluminum glass iron mica

Semiconductor devices can be manufactured to allow ____________ electrons to flow in one direction and ___ _________ electrons to flow in the opposite direction.

Electric Charges

Neutral State of an Atom

Elements are often identified by the number of electrons in orbit around the nucleus of the atoms making up the element and by the number of protons in the nucleus. A hydrogen atom, for example, has only one electron and one proton. An aluminum atom (illustrated) has 13 electrons and 13 protons. An atom with an equal number of electrons and protons is said to be electrically neutral.

Outer Band

Positive and Negative Charges

Electrons in the outer band of an atom are easily displaced by the application of some external force. Electrons which are forced out of their orbits can result in a lack of electrons where they leave and an excess of electrons where they come to rest. The lack of electrons is called a positive charge because there are more protons than electrons. The excess of electrons has a negative charge. A positive or negative charge is caused by an absence or excess of electrons. The number of protons remains constant.

Neutral Charge

Negative Charge

Positive Charge

7

Attraction and Repulsion of Electric Charges

The old saying, “opposites attract,” is true when dealing with electric charges. Charged bodies have an invisible electric field around them. When two like-charged bodies are brought together, their electric field will work to repel them. When two unlike-charged bodies are brought together, their electric field will work to attract them. The electric field around a charged body is represented by invisible lines of force. The invisible lines of force represent an invisible electrical field that causes the attraction and repulsion. Lines of force are shown leaving a body with a positive charge and entering a body with a negative charge. Unlike Charges Attract

Coulomb’s Law

8

Like Charges Repel

During the 18th century a French scientist, Charles A. Coulomb, studied fields of force that surround charged bodies. Coulomb discovered that charged bodies attract or repel each other with a force that is directly proportional to the product of the charges, and inversely proportional to the square of the distance between them. Today we call this Coulomb’s Law of Charges. Simply put, the force of attraction or repulsion depends on the strength of the charged bodies, and the distance between them.

Current

Electricity is the flow of free electrons in a conductor from one atom to the next atom in the same general direction. This flow of electrons is referred to as current and is designated by the symbol “I”. Electrons move through a conductor at different rates and electric current has different values. Current is determined by the number of electrons that pass through a cross-section of a conductor in one second. We must remember that atoms are very small. It takes about 1,000,000,000,000,000,000,000,000 atoms to fill one cubic centimeter of a copper conductor. This number can be simplified using mathematical exponents. Instead of writing 24 zeros after the number 1, write 1024. Trying to measure even small values of current would result in unimaginably large numbers. For this reason current is measured in amperes which is abbreviated “amps”. The letter “A” is the symbol for amps. A current of one amp means that in one second about 6.24 x 1018 electrons move through a cross-section of conductor. These numbers are given for information only and you do not need to be concerned with them. It is important, however, that the concept of current flow be unstood.

Units of Measurement

The following chart reflects special prefixes that are used when dealing with very small or large values of current: Prefix

Symbol

Decimal

1 kiloampere 1 milliampere 1 microampere

1 kA 1 mA 1 mA

1000 A 1/1000 A 1/1,000,000 A

9

Direction of Current Flow

Some authorities distinguish between electron flow and current flow. Conventional current flow theory ignores the flow of electrons and states that current flows from positive to negative. To avoid confusion, this book will use the electron flow concept which states that electrons flow from negative to positive.

_

+ Electron Flow

10

_

+ Conventional Current Flow

Voltage

Electricity can be compared with water flowing through a pipe. A force is required to get water to flow through a pipe. This force comes from either a water pump or gravity. Voltage is the force that is applied to a conductor that causes electric current to flow. Water Flow Through a Pipe

Current Flow Through a Conductor

Electrons are negative and are attracted by positive charges. They will always be attracted from a source having an excess of electrons, thus having a negative charge, to a source having a deficiency of electrons which has a positive charge. The force required to make electicity flow through a conductor is called a difference in potential, electromotive force (emf), or more simply referred to as voltage. voltage is designated by the letter “E”, or the letter “V”. The unit of measurement for voltage is volts which is also designated by the letter “V”.

11

Voltage Sources

An electrical voltage can be generated in various ways. A battery uses an electrochemical process. A car’s alternator and a power plant generator utilizes a magnetic induction process. All voltage sources share the characteristic of an excess of electrons at one terminal and a shortage at the other terminal. This results in a difference of potential between the two terminals. Shortage of Electrons Excess of Electrons

_

+

Batter y

Voltage Circuit Symbol

The terminals of a battery are indicated symbolically on an electrical drawing by two lines. The longer line indicates the positive terminal. The shorter line indicates the negative terminal.

+ _

Units of Measurement

12

The following chart reflects special prefixes that are used when dealing with very small or large values of voltage: Prefix

Symbol

Decimal

1 kilovolt 1 millivolt 1 microvolt

1 kV 1 mV 1 mV

1000 V 1/1000 V 1/1,000,000 V

Resistance

A third factor that plays a role in an electrical circuit is resistance. All material impedes the flow of electrical current to some extent. The amount of resistance depends upon composition, length, cross-section and temperature of the resistive material. As a rule of thumb, resistance of a conductor increases with an increase of length or a decrease of crosssection. Resistance is designated by the symbol “R”. The unit of measurement for resistance is ohms (Ω). Resistance Circuit Symbols

Resistance is usually indicated symbolically on an electrical drawing by one of two ways. An unfilled rectangle is commonly used. A zigzag line may also be used.

Resistance can be in the form of various components. A resistor may be placed in the circuit, or the circuit might contain other devices that have resistance. Units of Measurement

The following chart reflects special prefixes that are commonly used when dealing with values of resistance: Prefix

Symbol

Decimal

1 kilohm 1 megohm

1 kΩ 1 MΩ

1000 Ω 1,000,000 Ω

13

Review 2 1.

Elements are identified by the number of ____________ in orbit around the nucleus.

2.

A material that has an excess of electrons is said to have a ____________ charge.

3.

A material that has a deficiency of electrons is said to have a ____________ charge.

4.

Like charges ____________ and unlike charges ____________ .

5.

The force that is applied to a conductor to cause current flow is ____________ .

6.

Electrons move from ____________ . a. positive to negative b. negative to positive

7.

With an increase of length or a decrease of crosssection of a conductor, resistance will ____________ . a. increase b. decrease

14

Simple Electric Circuit

An Electric Circuit

A fundamental relationship exists between current, voltage, and resistance. A simple electric circuit consists of a voltage source, some type of load, and a conductor to allow electrons to flow between the voltage source and the load. In the following circuit a battery provides the voltage source, electrical wire is used for the conductor, and a light provides the resistance. An additional component has been added to this circuit, a switch. There must be a complete path for current to flow. If the switch is open, the path is incomplete and the light will not illuminate. Closing the switch completes the path, allowing electrons to leave the negative terminal and flow through the light to the positive terminal.

+

An Electrical Circuit Schematic

Switch

_

_

+

The following schematic is a representation of an electrical circuit, consisting of a battery, a resistor, a voltmeter and an ammeter. The ammeter, connected in series with the circuit, will show how much current flows in the circuit. The voltmeter, connected across the voltage source, will show the value of voltage supplied from the battery. Before an analysis can be made of a circuit, we need to understand Ohm’s Law. +

+ _

_ A

+ V

R

_

15

Ohm’s Law

George Simon Ohm and Ohm’s Law

The relationship between current, voltage and resistance was studied by the 19th century German mathematician, George Simon Ohm. Ohm formulated a law which states that current varies directly with voltage and inversely with resistance. From this law the following formula is derived: I=

E R

or Current =

Voltage Resistance

Ohm’s Law is the basic formula used in all electrical circuits. Electrical designers must decide how much voltage is needed for a given load, such as computers, clocks, lamps and motors. Decisions must be made concerning the relationship of current, voltage and resistance. All electrical design and analysis begins with Ohm’s Law. There are three mathematical ways to express Ohm’s Law. Which of the formulas is used depends on what facts are known before starting and what facts need to be known. I=

Ohm’s Law Triangle

16

E R

E=IxR

R=

E I

There is an easy way to remember which formula to use. By arranging current, voltage and resistance in a triangle, one can quickly determine the correct formula.

Using the Triangle

To use the triangle, cover the value you want to calculate. The remaining letters make up the formula.

I=

E R

E=IxR

R=

E I

Ohm’s Law can only give the correct answer when the correct values are used. Remember the following three rules: • • • Examples of Solving Ohm’s Law

Current is always expressed in amperes or amps Voltage is always expressed in volts Resistance is always expressed in ohms

Using the simple circuit below, assume that the voltage supplied by the battery is 10 volts, and the resistance is 5 Ω. +

_ A

+

+ _

V

R

_

To find how much current is flowing through the circuit, cover the “I” in the triangle and use the resulting equation. I=

E R

I=

10 Volts 5Ω

I = 2 Amps

Using the same circuit, assume the ammeter reads 200 mA and the resistance is known to be 10 Ω. To solve for voltage, cover the “E” in the triangle and use the resulting equation. E=IxR

E = 0.2 x 10

E = 2 Volts

Remember to use the correct decimal equivalent when dealing with numbers that are preceded with milli (m), micro (µ) or kilo (k). In this example had 200 been used instead of converting the value to 0.2, the wrong answer of 2000 volts would have been calculated.

17

DC Series Circuit

Resistance in a Series Circuit

A series circuit is formed when any number of resistors are connected end-to-end so that there is only one path for current to flow. The resistors can be actual resistors or other devices that have resistance. The following illustration shows four resistors connected end-to-end. There is one path of current flow from the negative terminal of the battery through R4, R3, R2, R1 returning to the positive terminal. R1

R3

R2

R4

+ _

Formula for Series Resistance

The values of resistance add in a series circuit. If a 4 Ω resistor is placed in series with a 6 Ω resistor, the total value will be 10 Ω. This is true when other types of resistive devices are placed in series. The mathematical formula for resistance in series is: Rt = R1 + R2 + R3 + R4 + R5 11 KΩ

2 KΩ

2 KΩ

100 Ω

1 KΩ

R1

R2

R3

R4

R5

+ _

Rt = R1 + R2 + R3 + R4 + R5 Rt = 11,000 + 2,000 + 2,000 + 100 + 1,000 Rt = 16,100 Ω

18

Current in a Series Circuit

The equation for total resistance in a series circuit allows us to simplify a circuit. Using Ohm’s Law, the value of current can be calculated. Current is the same anywhere it is measured in a series circuit. E R 12 I= 10 I=

I = 1.2 Amps

+ _

5Ω

1Ω

2Ω

2Ω

10 Ω

R1

R2

R3

R4

Rt + _

12 Volts

Equivalent Circuit

Original Circuit

Voltage in a Series Circuit

12 Volts

Voltage can be measured across each of the resistors in a circuit. The voltage across a resistor is referred to as a volt age drop. A German physicist, Kirchhoff, formulated a law which states the sum of the voltage drops across the resistances of a closed circuit equals the total voltage applied to the circuit. In the following illustration, four equal value resistors of 1.5 Ω each have been placed in series with a 12 volt battery. Ohm’s Law can be applied to show that each resistor will “drop” an equal amount of voltage. 12 V

3V

3V

3V

3V

1.5 Ω

1.5 Ω

1.5 Ω

1.5 Ω

R1

R2

R3

R4

12 Volt Battery +

_

19

First, solve for total resistance: Rt = R1 + R2 + R3 + R4 Rt = 1.5 + 1.5 + 1.5 + 1.5 Rt = 6 Ω

Second, solve for current: I= E R I = 12 6 I = 2 Amps

Third, solve for voltage across any resistor: E=IxR E = 2 x 1.5 E = 3 Volts

If voltage were measured across any single resistor, the meter would read three volts. If voltage were read across a combination of R3 and R4 the meter would read six volts. If voltage were read across a combination of R2, R3, and R4 the meter would read nine volts. If the voltage drops of all four resistors were added together the sum would be 12 volts, the original supply voltage of the battery. Voltage Division in a Series Circuit

It is often desirable to use a voltage potential that is lower than the supply voltage. To do this, a voltage divider, similar to the one illustrated, can be used. The battery represents Ein which in this case is 50 volts. The desired voltage is represented by Eout, which mathematically works out to be 40 volts. To calculate this voltage, first solve for total resistance. Rt = R1 + R2 Rt = 5 + 20 Rt = 25 Ω

20

Second, solve for current: Ein Rt 50 I= 25 I=

I = 2 Amps

Finally, solve for voltage: Eout = I x R2 Eout = 2 x 20 Eout = 40 Volts

+ _

Ein

R1

5Ω

R2

20 Ω

Eout 40 Volts

21

Review 3 1.

The basic Ohm’s Law formula is ____________ .

2.

When solving circuit problems; current must always be expressed in ____________ , voltage must always be expressed in ____________ and resistance must always be expressed in ____________ .

3.

The total current of a simple circuit with a voltage supply of 12 volts and a resistance of 24 Ω is ____________ amps.

4.

What is the total resistance of a series circuit with the following values: R1=10 Ω, R2=15 Ω, and R3=20 Ω? ____________ Ω.

5.

What is total current of a series circuit that has a 120 volt supply and 60 Ω resistance?

6.

In the following circuit the voltage dropped across R1 is ____________ volts and R2 is ____________ volts.

+ _

7.

1.5 Ω

R1

R2

12 Volts

In the following circuit voltage dropped across R1 is ____________ volts, and R2 is ____________ volts.

+ _

22

1.5 Ω

5Ω

20 Ω

R1

R2

100 Volts

DC Parallel Circuit

Resistance in a Parallel Circuit

A parallel circuit is formed when two or more resistances are placed in a circuit side-by-side so that current can flow through more than one path. The illustration shows two resistors placed side-by-side. There are two paths of current flow. One path is from the negative terminal of the battery through R1 returning to the positive terminal. The second path is from the negative terminal of the battery through R2 returning to the positive terminal of the battery.

+ _

Formula for Equal Value Resistors in a Parallel Circuit

R1

R2

To determine the total resistance when resistors are of equal value in a parallel circuit, use the following formula: Rt =

Value of any one Resistor Number of Resistors

In the following illustration there are three 15 Ω resistors. The total resistance is: Rt =

Value of any one Resistor Number of Resistor

15 Rt = 3 Rt = 5 Ω

+ _

R1

R1

R1

15 Ω

15 Ω

15 Ω

23

Formula for Unequal There are two formulas to determine total resistance for Resistors in a Parallel Circuit unequal value resistors in a parallel circuit. The first formula is used when there are three or more resistors. The formula can be extended for any number of resistors. 1 = 1 + 1 + 1 Rt R1 R2 R3

In the following illustration there are three resistors, each of different value. The total resistance is: 1 = 1 + 1 + 1 Rt R1 R2 R3 1 = Rt

Insert Value of the Resistors

1 = 4 + 2 + 1 Rt 20 20 20

Find Lowest Common Denominator

1 = 7 Rt 20

Add the Numerators

Rt = 20 1 7

Invert Both Sides of the Equation

Rt = 2.86 Ω

Divide

+ _

24

1 + 1 + 1 10 5 20

R1

R2

R3

5Ω

10 Ω

20 Ω

The second formula is used when there are only two resistors. R1 x R2 Rt = R1 + R2

In the following illustration there are two resistors, each of different value. The total resistance is: R1 x R2 Rt = R1 + R2 5 x 10 5 + 10

Rt =

50 Rt = 15 Rt =

3.33 Ω

+ _

Voltage in a Parallel Circuit

R1 5Ω

R2 10 Ω

When resistors are placed in parallel across a voltage source, the voltage is the same across each resistor. In the following illustration three resistors are placed in parallel across a 12 volt battery. Each resistor has 12 volts available to it. 12 Volt Battery + _

R1

12 V

R2

12 V

R3

12 V

25

Current in a Parallel Circuit

Current flowing through a parallel circuit divides and flows through each branch of the circuit. It

+ _

R1

R2

I1

I2

R3 I3

It

Total current in a parallel circuit is equal to the sum of the current in each branch. The following formula applies to current in a parallel circuit. It = I 1 + I 2 + I 3

Current Flow with Equal Value Resistors in a Parallel Circuit

When equal resistances are placed in a parallel circuit, opposition to current flow is the same in each branch. In the following circuit R1 and R2 are of equal value. If total current (It) is 10 amps, then 5 amps would flow through R1 and 5 amps would flow through R2. It = 10 Amps

+ _

R1 I1 = 5 Amps

R2 I2 = 5 Amps

It = 10 Amps It = I 1 + I 2 It = 5 Amps + 5 Amps It = 10 Amps

26

Current Flow with Unequal Value Resistors in a Parallel Circuit

When unequal value resistors are placed in a parallel circuit, opposition to current flow is not the same in every circuit branch. Current is greater through the path of least resistance. In the following circuit R1 is 40 Ω and R2 is 20 Ω. Small values of resistance means less opposition to current flow. More current will flow through R2 than R1.

12 Volts + _

R1 40 Ω I1 = 0.3 Amps

R2 20 Ω I2 = 0.6 Amps

It = 0.9 Amps

Using Ohm’s Law, the total current for each circuit can be calculated. I1 =

E R1

I1 = 120 Volts 40 Ω I1 = 0.3 Amps

I2 =

E R2

I2 = 120 Volts 20 Ω I2 = 0.6 Amps

It = I 1 + I 2 It = 0.3 Amps + 0.6 Amps It = 0.9 Amps

27

Total current can also be calculated by first calculating total resistance, then applying the formula for Ohm’s Law. R1 x R2 Rt = R1 + R2 40 Ω x 20 Ω Rt = 40 Ω + 20 Ω 800 Ω Rt = 60 Ω Rt = 13.333 Ω

It = E Rt It = 12 Volts 13.333 Ω It = 0.9 Amps

28

Review 4 1.

The total resistance of a parallel circuit that has four 20 Ω resistors is ____________ Ω.

2.

Rt for the following circuit is ____________ Ω.

+ _

3.

R2

R3

10 Ω

20 Ω

30 Ω

Rt for the following circuit is ____________ Ω.

+ _

4.

R1

R1 5Ω

R2 10 Ω

Voltage available at R2 in the following circuit is ____________ volts. 12 Volts

+ _

R1 5Ω

R2 10 Ω

5.

In a parallel circuit with two resistors of equal value and a total current flow of 12 amps, the value of current through each resistor is ____________ amps.

6.

In the following circuit current flow through R1 is _____ _______ amps, and R2 is ____________ amps. 24 Volts + _

R1 10 Ω

R2 10 Ω

29

Series-Parallel Circuits

Series-parallel circuits are also known as compound circuits. At least three resistors are required to form a series-parallel circuit. The following illustrations show two ways a series-parallel combination could be found. Parallel Branches + _

Parallel Branches Devices in Series + _

Simplifying a Series-Parallel

The formulas required for solving current, voltage and resistance problems have already been defined. To solve a series-parallel circuit, reduce the compound circuits to equivalent simple circuits. In the following illustration R1 and R2 are parallel with each other. R3 is in series with the parallel circuit of R1 and R2. R1 10 Ω R3 10 Ω + _

30

R2 10 Ω

First, use the formula to determine total resistance of a parallel circuit to find the total resistance of R1 and R2. When the resistors in a parallel circuit are equal, the following formula is used: R =

Value of any One Resistor Number of Resistors

R = 10 Ω 2 R = 5Ω

Second, redraw the circuit showing the equivalent values. The result is a simple series circuit which uses already learned equations and methods of problem solving. R3 10Ω

R3 5Ω

+ _

Simplifying a Series-Parallel Circuit to a Parallel Circuit

In the following illustration R1 and R2 are in series with each other. R3 is in parallel with the series circuit of R1 and R2.

R1 10Ω + _

R3 20Ω R2 10Ω

First, use the formula to determine total resistance of a series circuit to find the total resistance of R1 and R2. The following formula is used: R = R1 + R 2 R = 10 Ω + 10 Ω R = 20 Ω

31

Second, redraw the circuit showing the equivalent values. The result is a simple parallel circuit which uses already learned equations and methods of problem solving.

+ _

+ _

32

R = 20 Ω

R3 = 20 Ω

Rt = 10 Ω

Review 5 1.

Calculate equivalent resistance for R1 and R2 and total resistance for the entire circuit. R1 20 Ω R3 10 Ω

+ _

R2 30 Ω

R1/R2 equivalent resistance = ____________ Ω Total resistance = ____________ Ω 2.

Calculate equivalent resistance for R1 and R2 and total resistance for the entire circuit.

R1 30 Ω + _

R3 20 Ω R2 10 Ω

R1/R2 equivalent resistance = ____________ Ω Total resistance = ____________ Ω

33

Power

Work

Whenever a force of any kind causes motion, work is accomplished. In the illustration below work is done when a mechanical force is used to lift a weight. If a force were exerted without causing motion, then no work is done.

Electric Power

In an electrical circuit, voltage applied to a conductor will cause electrons to flow. Voltage is the force and electron flow is the motion. The rate at which work is done is called power and is represented by the symbol “P”. Power is measured in watts and is represented by the symbol “W”. The watt is defined as the rate work is done in a circuit when 1 amp flows with 1 volt applied.

Power Formulas

Power consumed in a resistor depends on the amount of current that passes through the resistor for a given voltage. This is expressed as voltage times current. P=ExI or P = EI

Power can also be calculated by substituting other components of Ohm’s Law. P = I2R and P=

34

E2 R

Solving a Power Problem

In the following illustration power can be calculated using any of the power formulas. I = 2 Amps + _

12 Volts

R=6Ω

P = EI P = 12 Volts x 2 Amps P = 24 Watts P = I2 R P = (2 Amps)2 x 6 Ω P = 24 Watts P=

E2 R

P=

(12 Volts)2 6Ω

P=

144 6

P = 24 Watts

Power Rating of Equipment

Electrical equipment is rated in watts. This rating is an indication of the rate at which electrical equipment converts electrical energy into other forms of energy, such as heat or light. A common household lamp may be rated for 120 volts and 100 watts. Using Ohm’s Law, the rated value of resistance of the lamp can be calculated. P=

E2 R

2 which can be transposed to R = E P

R=

(120 Volts)2 100 Watts

R = 144 Ω

35

Using the basic Ohm’s Law formula, the amount of current flow for the 120 volt, 100 watt lamp can be calculated. I= I=

E R 120 Volts 144 Ω

I = 0.833 Amps

A lamp rated for 120 volts and 75 watts has a resistance of 192 Ω and a current of 0.625 amps would flow if the lamp had the rated voltage applied to it. R=

E2 P

R=

(120 Volts)2 75 Watts

R = 192 Ω I=

E2 P

I=

120 Volts 192 Ω

I = 0.625 Amps

It can be seen that the 100 watt lamp converts energy faster than the 75 watt lamp. The 100 watt lamp will give off more light and heat. Heat

36

Current flow through a resistive material causes heat. An electrical component can be damaged if the temperature is too high. For this reason, electrical equipment is often rated for a maximum wattage. The higher the wattage rating, the more heat the equipment can dissipate.

Magnetism

The principles of magnetism are an integral part of electricity. Electromagnets are used in some direct current circuits. Alternating current cannot be understood without first understanding magnetism. Types of Magnets

The three most common forms of magnets are the horse-shoe, bar and compass needle.

All magnets have two characteristics. They attract and hold iron. If free to move, like the compass needle, the magnet will assume roughly a north-south position. Magnetic Lines of Flux

Every magnet has two poles, one north pole and one south pole. Invisible magnetic lines of flux leave the north pole and enter the south pole. While the lines of flux are invisible, the effects of magnetic fields can be made visible. When a sheet of paper is placed on a magnet and iron filings loosely scattered over it, the filings will arrange themselves along the invisible lines of flux.

37

By drawing lines the way the iron filings have arranged themselves, the following picture is obtained. Broken lines indicate the paths of magnetic flux lines. The field lines exist outside and inside the magnet. The magnetic lines of flux always form closed loops. Magnetic lines of flux leave the north pole and enter the south pole, returning to the north pole through the magnet.

Interaction between Two Magnets

38

When two magnets are brought together, the magnetic flux field around the magnet causes some form of interaction. Two unlike poles brought together cause the magnets to attract each other. Two like poles brought together cause the magnets to repel each other.

Electromagnetism

Left-Hand Rule for Conductors

An electromagnetic field is a magnetic field generated by current flow in a conductor. Whenever current flows a magnetic field exists around the conductor. Every electric current generates a magnetic field. A definite relationship exists between the direction of current flow and the direction of the magnetic field. The left-hand rule for conductors demonstrates this relationship. If a current-carrying conductor is grasped with the left hand with the thumb pointing in the direction of electron flow, the fingers will point in the direction of the magnetic lines of flux.

Current-Carrying Coil

A coil of wire carrying a current, acts like a magnet. Individual loops of wire act as small magnets. The individual fields add together to form one magnet. The strength of the field can be increased by adding more turns to the coil. The strength can also be increased by increasing the current.

39

Left-Hand Rule for Coils

A left-hand rule exists for coils to determine the direction of the magnetic field. The fingers of the left hand are wrapped around the coil in the direction of electron flow. The thumb points to the north pole of the coil.

Electromagnets

An electromagnet is composed of a coil of wire wound around a core. The core is usually a soft iron which conducts magnetic lines of force with relative ease. When current is passed through the coil, the core becomes magnetized. The ability to control the strength and direction of the magnetic force makes electromagnets useful. As with permanent magnets, opposite poles attract. An electromagnet can be made to control the strength of its field which controls the strength of the magnetic poles. A large variety of electrical devices such as motors, circuit breakers, contactors, relays and motor starters use electromagnetic principles.

40

Review 6 1.

The rate at which work is done is called ___________ .

2.

The basic formula for power is ____________ .

3.

In a circuit with a 12 volt supply and 4 Ω resistance the power consumed is ____________ watts.

4.

The two characteristics of all magnets are; they attract and hold ____________ , and if free to move will assume roughly a ____________ position.

5.

Lines of flux always leave the ____________ pole and enter the ____________ pole.

6.

The left-hand rule for conductors states that when the ___________ hand is placed on a current-carrying conductor with the ____________ pointing in the direction of electron flow, the fingers will point in the direction of ____________ .

41

Introduction to AC

The supply of current for electrical devices may come from a direct current source (DC), or an alternating current source (AC). In direct current electricity, electrons flow continuously in one direction from the source of power through a conductor to a load and back to the source of power. Voltage in direct current remains constant. DC power sources include batteries and DC generators. In allowing current an AC generator is used to make electrons flow first in one direction then in another. Another name for an AC generator is an alternator. The AC generator reverses terminal polarity many times a second. Electrons will flow through a conductor from the negative terminal to the positive terminal, first in one direction then another.

42

AC Sine Wave

Alternating voltage and current vary continuously. The graphic representation for AC is a sine wave. A sine wave can represent current or voltage. There are two axes. The vertical axis represents the direction and magnitude of current or voltage. The horizontal axis represents time. + Direction

0

Time

- Direction

When the waveform is above the time axis, current is flowing in one direction. This is referred to as the positive direction. When the waveform is below the time axis, current is flowing in the opposite direction. This is referred to as the negative direction. A sine wave moves through a complete rotation of 360 degrees, which is referred to as one cycle. Alternating current goes through many of these cycles each second. The unit of measurement of cycles per second is hertz. In the United States alternating current is usually generated at 60 hertz. Single-Phase and Three-Phase AC Power

Alternating current is divided into single-phase and three-phase types. Single-phase power is used for small electrical demands such as found in the home. Three-phase power is used where large blocks of power are required, such as found in commercial applications and industrial plants. Single-phase power is shown in the above illustration. Three-phase power, as shown in the following illustration, is a continuous series of three overlapping AC cycles. Each wave represents a phase, and is offset by 120 electrical degrees. Phase 1 Phase 2 Phase 3 +

0

-

43

AC Generators

Basic Generator

A basic generator consists of a magnetic field, an armature, slip rings, brushes and a resistive load. The magnetic field is usually an electromagnet. An armature is any number of conductive wires wound in loops which rotates through the magnetic field. For simplicity, one loop is shown. When a conductor is moved through a magnetic field, a voltage is induced in the conductor. As the armature rotates through the magnetic field, a voltage is generated in the armature which causes current to flow. Slip rings are attached to the armature and rotate with it. Carbon brushes ride against the slip rings to conduct current from the armature to a resistive load.

Pole Piece

Magnetic Field Armature

Brush

R1

Slip Ring

Basic Generator Operation

An armature rotates through the magnetic field. At an initial position of zero degrees, the armature conductors are moving parallel to the magnetic field and not cutting through any magnetic lines of flux. No voltage is induced.

R1

44

Generator Operation from Zero to 90 Degrees

The armature rotates from zero to 90 degrees. The conductors cut through more and more lines of flux, building up to a maximum induced voltage in the positive direction. 90 Degrees

R1

Generator Operation from 90 to 180 Degrees

The armature continues to rotate from 90 to 180 degrees, cutting less lines of flux. The induced voltage decreases from a maximum positive value to zero.

S

180 Degrees

R1

Generator Operation from

The armature continues to rotate from 180 degrees to 270 degrees. The conductors cut more and more lines of flux, but in the opposite direction. voltage is induced in the negative direction building up to a maximum at 270 degrees.

270 Degrees

R1

45

Generator Operation from 270 to 360 Degrees

The armature continues to rotate from 270 to 360 degrees. Induced voltage decreases from a maximum negative value to zero. This completes one cycle. The armature will continue to rotate at a constant speed. The cycle will continuously repeat as long as the armature rotates. 360 Degrees

S

One Revolution R1

46

Frequency

The number of cycles per second made by voltage induced in the armature is the frequency of the generator. If the armature rotates at a speed of 60 revolutions per second, the generated voltage will be 60 cycles per second. The accepted term for cycles per second is hertz. The standard frequency in the United States is 60 hertz. The following illustration shows 15 cycles in 1/4 second which is equivalent to 60 cycles in one second.

1/4 Second

Four-Pole AC Generator

The frequency is the same as the number of rotations per second if the magnetic field is produced by only two poles. An increase in the number of poles, would cause an increase in the number of cycles completed in a revolution. A two-pole generator would complete one cycle per revolution and a fourpole generator would complete two cycles per revolution. An AC generator produces one cycle per revolution for each pair of poles.

One Revolution R1

47

Voltage and Current

Peak Value

The sine wave illustrates how voltage and current in an AC circuit rises and falls with time. The peak value of a sine wave occurs twice each cycle, once at the positive maximum value and once at the negative maximum value. Peak Value

+

0

Time

-

Peak-to-Peak Value

Peak Value

The value of the voltage or current between the peak positive and peak negative values is called the peak-to-peak value. +

0

Peak-to-Peak Value

Time

-

Instantaneous Value

The instantaneous value is the value at any one particular time. It can be in the range of anywhere from zero to the peak value. +

0

-

48

Instantaneous Value

Time

Calculating Instantaneous Voltage

The voltage waveform produced as the armature rotates through 360 degrees rotation is called a sine wave because instantaneous voltage is related to the trigonometric function called sine (sin θ = sine of the angle). The sine curve represents a graph of the following equation: e = Epeak x sin θ

Instantaneous voltage is equal to the peak voltage times the sine of the angle of the generator armature. The sine value is obtained from trigonometric tables. The following table reflects a few angles and their sine value. Angle

Sin

θ

Angle

Sin

θ

30 Degrees

0.5

210 Degrees

-0.5

60 Degrees

0.866

240 Degrees

-0.866

90 Degrees

1

270 Degrees

-1

120 Degrees

0.866

300 Degrees

-0.866

150 Degrees

0.5

330 Degrees

-0.5

180 Degrees

0

360 Degrees

0

The following example illustrates instantaneous values at 90, 150, and 240 degrees. The peak voltage is equal to 100 volts. By substituting the sine at the instantaneous angle value, the instantaneous voltage can be calculated. 90° = +100 Volts

+

150° = +50 Volts 0 240° = -86.6 Volts -

Any instantaneous value can be calculated. For example: 240° e = 100 x -0.866 e = -86.6 volts

49

Effective Value of an AC Sine Wave

Alternating voltage and current are constantly changing values. A method of translating the varying values into an equivalent constant value is needed. The effective value of voltage and current is the common method of expressing the value of AC. This is also known as the RMS (root-mean-square) value. If the voltage in the average home is said to be 120 volts, this is the RMS value. The effective value figures out to be 0.707 times the peak value. + Peak Value 169.7 Volts 0

-

169.7 Vpeak x 0.707 = 120 Vrms

The effective value of AC is defined in terms of an equivalent heating effect when compared to DC. One RMS ampere of current flowing through a resistance will produce heat at the same rate as a DC ampere. For purpose of circuit design, the peak value may also be needed. For example, insulation must be designed to withstand the peak value, not just the effective value. It may be that only the effective value is known. To calculate the peak value, multiply the effective value by 1.41. For example, if the effective value is 100 volts, the peak value is 141 volts. Review 7

50

1.

The graphic representation of AC voltage or current values over a period of time is a ____________ ____________ .

2.

Each phase of three phase AC power is offset by ____________ degrees.

3.

An AC generator produces ____________ cycle per revolution for each pair of poles.

4.

What is the instantaneous voltage at 240 degrees for a peak voltage of 150 volts?

5.

What is the effective voltage for a peak voltage of 150 volts?

Inductance

The circuits studied to this point have been resistive. Resistance and voltage are not the only circuit properties that effect current flow, however. Inductance is the property of an electric circuit that opposes any change in electric current. Resistance opposes current flow, inductance opposes change in current flow. Inductance is designated by the letter “L”. . The unit of measurement for inductance is the henry (h). Current Flow and Field Strength

Current flow produces a magnetic field in a conductor. The amount of current determines the strength of the magnetic field. As current flow increases, field strength increases, and as current flow decreases, field strength decreases. 0 Degrees No Current

30 Degrees Increasing Current

90 Degrees Maximum Current

Any change in current causes a corresponding change in the magnetic field surrounding the conductor. Current is constant in DC, except when the circuit is turned on and off, or when there is a load change. Current is constantly changing in AC, so inductance is a continual factor. A change in the magnetic field surrounding the conductor induces a voltage in the conductor. This self-induced voltage opposes the change in current. This is known as counter emf. This opposition causes a delay in the time it takes current to attain its new steady value. If current increases, inductance tries to hold it down. If current decreases, inductance tries to hold it up. Inductance is somewhat like mechanical inertia which must be overcome to get a mechanical object moving or to stop a mechanical object from moving. A vehicle, for example, takes a few moments to accelerate to a desired speed, or decelerate to a stop.

51

Inductors

Inductance is usually indicated symbolically on an electrical drawing by one of two ways. A curled line or a filled rectangle can be used.

Inductors are coils of wire. They may be wrapped around a core. The inductance of a coil is determined by the number of turns in the coil, the spacing between the turns, the coil diameter, the core material, the number of layers of windings, the type of winding, and the shape of the coil. Examples of inductors are transformers, chokes, and motors. Simple Inductive Circuit

In a resistive circuit, current change is considered instantaneous. If an inductor is used, the current does not change as quickly. In the following circuit, initially the switch is open and there is no current flow. When the switch is closed, current will rise rapidly at first, then more slowly as the maximum value is approached. For the purpose of explanation, a DC circuit is used.

+ _

R1 L1

Inductive Time Constant

52

The time required for the current to rise to its maximum value is determined by the ratio of inductance (in henrys) to resistance (in ohms). This ratio is called the time constant of the inductive circuit. A time constant is the time (in seconds) required for the circuit current to rise to 63.2% of its maximum value. When the switch is closed in the previous circuit, current will begin to flow. During the first time constant current rises to 63.2% of its maximum value. During the second time constant, current rises to 63.2% of the remaining 36.8%, or a total of 86.4%. It takes about five time constants for current to reach its maximum value.

100.0% 98.1% 94.9% 86.4%

63.2%

First Time Constant

Second Time Constant

Third Time Constant

Fourth Time Constant

Fifth Time Constant

Similarly, when the switch is opened, it will take five time constants for current to reach zero. It can be seen that inductance is an important factor in AC circuits. If the frequency is 60 hertz, current will rise and fall from its peak value to zero 120 times a second. 100.0%

First Time Constant


Third Time Constant


Fifth Time Constant

36.8% 13.6% 5.1% 1.9% 0%

Calculating the Time Constant of an Inductive Circuit

The time constant is designated by the symbol “τ”. To determine the time constant of an inductive circuit use one of the following formulas: τ (in seconds) =

L (henrys) R (ohms)

τ (in milliseconds) =

L (millihenrys) R (ohms)

τ (in microseconds) =

L (microhenrys) R (ohms)

53

In the following illustration, L1 is equal to 15 millihenrys and R1 is equal to 5 Ω. When the switch is closed, it will take 3 milliseconds for current to rise from zero to 63.2% of its maximum value.

+ _

R1 5 Ω L1 15 mh

τ=

15 mh 5Ω

τ = 3 milliseconds

Formula for Series Inductors The same rules for calculating total resistance can be applied. In the following circuit, an AC generator is used to supply electrical power to four inductors. There will always be some amount of resitance and inductance in any circuit. The electrical wire used in the circuit and the inductors both have some resistance and inductance. Total inductance is calculated using the following formula: Lt = L 1 + L 2 + L 3

R1

2 mh

2 mh

1 mh

1 mh

L1

L2

L3

L4

AC Generator

Lt = L1 + L2 + L3 + L4 Lt = 2 mh + 2 mh + 1 mh + 1 mh Lt = 6 mh

54

Formula for Parallel Inductors

In the following circuit, an AC generator is used to supply electrical power to three inductors. Total inductance is calculated using the following formula: 1 = 1 + 1 + 1 Lt L1 L2 L3

R1

1 = Lt

L1

L2

L3

5 mh

10 mh

20 mh

1 + 1 + 1 5 10 20

1 = 7 Lt 20 Lt = 2.86 mh

55

Capacitance

Capacitance and Capacitors

Capacitance is a measure of a circuit’s ability to store an elec cal charge. A device manufactured to have a specific amount of capacitance is called a capacitor. A capacitor is made up of a pair of conductive plates separated by a thin layer of insulating material. Another name for the insulating material is dielectric material. When a voltage is applied to the plates, electrons are forced onto one plate. That plate has an excess of electrons while the other plate has a deficiency of electrons. The plate with an excess of electrons is negatively charged. The plate with a deficiency of electrons is positively charged. Negative Plate Dielectric Material Positive Plate

Direct current cannot flow through the dielectric material because it is an insulator; however it can be used to charge a capacitor. Capacitors have a capacity to hold a specific quantity of electrons. The capacitance of a capacitor depends on the area of the plates, the distance between the plates, and the material of the dielectric. The unit of measurement for capacitance is farads (F). Capacitors usually are rated in µF (microfarads), or pF (picofarads). Capacitor Circuit Symbols

56

Capacitance is usually indicated symbolically on an electrical drawing by a combination of a straight line with a curved line, or two straight lines.

Simple Capacitive Circuit

In a resistive circuit, voltage change is considered instantaneous. If a capacitor is used, the voltage across the capacitor does not change as quickly. In the following circuit, initially the switch is open and no voltage is applied to the capacitor. When the switch is closed, voltage across the capacitor will rise rapidly at first, then more slowly as the maximum value is approached. For the purpose of explanation, a DC circuit is used.

+ _

R1 C1

Capacitive Time Constant

The time required for voltage to rise to its maximum value in a circuit containing capacitance is determined by the product of capacitance, in farads, times resistance, in ohms. This product is the time constant of a capacitive circuit. The time constant gives the time in seconds required for voltage across the capacitor to reach 63.2% of its maximum value. When the switch is closed in the previous circuit, voltage will be applied. During the first time constant, voltage will rise to 63.2% of its maximum value. During the second time constant, voltage will rise to 63.2% of the remaining 36.8%, or a total of 86.4%. It takes about five time constants for voltage across the capacitor to reach its maximum value. 100.0% 98.1% 94.9% 86.4%

63.2%

First Time Constant


Third Time Constant


Fifth Time Constant

57

Similarly, during this same time, it will take five time constants for current through the resistor to reach zero. 100.0%

First Time Constant


Third Time Constant


Fifth Time Constant

36.8% 13.6% 5.1% 1.9% 0%

Calculating the Time Constant of a Capacitive Circuit

To determine the time constant of a capacitive circuit, use one of the following formulas: τ (in seconds) = R (megohms) x C (microfarads) τ (in microseconds) = R (megohms) x C (picofarads) τ (in microseconds) = R (ohms) x C (microfarads)

In the following illustration, C1 is equal to 2 µF, and R1 is equal to 10 Ω. When the switch is closed, it will take 20 microseconds for voltage across the capacitor to rise from zero to 63.2% of its maximum value. It will take five time constants, 100 microseconds for this voltage to rise to its maximum value.

+ _

R1 10 Ω C1 2µF

V τ = RC τ = 2µF x 10 Ω τ = 20 microseconds

58

Formula for Series Capacitors

Connecting capacitors in series decreases total capacitance. The effect is like increasing the space between the plates. The formula for series capacitors is similar to the formula for parallel resistors. In the following circuit, an AC generator supplies electrical power to three capacitors. Total capacotance is calculated using the following formula: 1 = 1 + 1 + 1 Ct C1 C2 C3

R1

5 µF

10 µF

20 µF

C1

C2

C3

1 = 1 + 1 + 1 Ct 5 10 20 1 = 7 Ct 20 Ct = 2.86 µF

Formula for Parallel Capacitors

In the following circuit, an AC generator is used to supply electrical power to three capacitors. Total capacitance is calculated using the following formula: Ct = C1 + C2 + C3

R1 C1

C2

C3

5 µF

10 µF

20 µF

Ct = 5 µF + 10 µF + 20 µF Ct = 35 µF

59

Review 8 1.

The total inductance for this circuit is ___________ .

R1

2.

4 mh

2 mh

L1

L2

3 mh

1 mh

L3

L4

The total inductance for this circuit is ____________ . R1 L1 5 mh

3.

L3 10 mh

The total capacitance for this circuit is ____________ .

R1

4.

L2 10 mh

5 µF

10 µF

10 µF

C1

C2

C3

The total capacitance for this circuit is ____________ . R1

60

C1

C2

C3

5 µF

10 µF

10 µF

Inductive and Capacitive Reactance

In a purely resistive AC circuit, opposition to current flow is called resistance. In an AC circuit containing only inductance, capacitance, or both, opposition to current flow is called reactance. Total opposition to current flow in an AC circuit that contains both reactance and resistance is called impedance, designated by the symbol “Z”. Reactance and impedance are expressed in ohms. Inductive Reactance

Inductance only affects current flow when the current is changing. Inductance produces a self-induced voltage (counter emf) that opposes changes in current. In an AC circuit, current is changing constantly. Inductance in an AC circuit, therefore, causes a continual opposition. This opposition to current flow is called inductive reactance and is designated by the symbol XL. Inductive reactance is dependent on the amount of inductance and frequency. If frequency is low, current has more time to reach a higher value before the polarity of the sine wave reverses. If frequency is high, current has less time to reach a higher value. In the following illustration, voltage remains constant. Current rises to a higher value at a lower frequency than a higher frequency. +

+ Current

Current

0

0

_

_ Low Frequency

High Frequency

The formula for inductive reactance is: XL = 2πfL XL = 2 x 3.14 x frequency x inductance

61

In a 60 hertz, 10 volt circuit containing a 10 mh inductor, the inductive reactance would be: XL = 2πfL XL = 2 x 3.14 x 60 x 0.10 XL = 3.768 Ω

Once inductive reactance is known, Ohm’s Law can be used to calculate reactive current. I=

E Z

I=

10 3.768

I = 2.65 Amps

Phase Relationship between Current and Voltage in an Inductive Circuit

Current does not rise at the same time as the source voltage in an inductive circuit. Current is delayed depending on the amount of inductance. In a purely resistive circuit, current and voltage rise and fall at the same time. They are said to be “in phase.” In this circuit there is no inductance. Resistance and impedance are the same. +

Voltage Current

0

_

In a purely inductive circuit, current lags behind voltage by 90 degrees. Current and voltage are said to be “out of phase”. In this circuit, impedance and inductive reactance are the same. 90 Degrees +

Voltage Current

0

_

62

All inductive circuits have some amount of resistance. AC current will lag somewhere between a purely resistive circuit, and a purely inductive circuit. The exact amount of lag depends on the ratio of resistance and inductive reactance. The more resistive a circuit is, the closer it is to being in phase. The more inductive a circuit is, the more out of phase it is. In the following illustration, resistance and inductive reactance are equal. Current lags voltage by 45 degrees. 45 Degrees +

XL = 10 Ω Voltage Current

0 R = 10 Ω _

Calculating Impedance in an Inductive Circuit

When working with a circuit containing elements of inductance, capacitance, and resistance, impedance must be calculated. Because electrical concepts deal with trigonometric functions, this is not a simple matter of subtraction and addition. The following formula is used to calculate impedance in an inductive circuit: Z = R2 + XL2

In the circuit illustrated above, resistance and inductive reactance are each 10 ohms. Impedance is 14.1421 ohms. A simple application of Ohm’s Law can be used to find total circuit current. Z = 102 + 102 Z=

200

Z = 14.1421 Ω

Vectors

Another way to represent this is with a vector. A vector is a graphic represention of a quantity that has direction and magnitude. A vector on a map might indicate that one city is 50 miles southwest from another. The magnitude is 50 miles and the direction is southwest. Vectors are also used to show electrical relationships. As mentioned earlier, impedance (Z) is the total opposition to current flow in an AC circuit containing reactance, inductance, and capacitance.

63

14 .14 2

1

Ω

The following vector illustrates the relationship between reactance and inductive reactance of a circuit containing equal values of each. The angle between the vectors is the phase angle represented by the symbol θ. When inductive reactance is equal to resistance the resultant angle is 45 degrees. It is this angle that determines how much current will lag voltage.

Z

=

XL = 10 Ω

θ R = 10 Ω

Capacitive Reactance

Capacitance also opposes AC current flow. Capacitive reactance is designated by the symbol XC.The larger the capacitor, the smaller the capacitive reactance. Current flow in a capacitive AC circuit is also dependent on frequency. The following formula is used to calculate capacitive reactance. 1 XC = 2πfC

Capacitive reactance is equal to 1 divided by 2 times pi, times the frequency, times the capacitance. The capacitive reactance for a 60 hertz circuit with a 10 microfarad capacitor is: 1 XC = 2πfC 1 XC = 2 x 3.14 x 60 x 0.000010 XC = 265.39 Ω

Once capacitive reactance is known, Ohm’s Law can be used to calculate reactive current. I=

E Z

I=

10 265.39

I = 0.0376 Amps

64

Phase Relationship between The phase relationship between current and voltage are Current and Voltage opposite to the phase relationship of an inductive circuit. In a purely capacitive circuit, current leads voltage by 90 degrees. 90 Degrees +

Voltage Current

0

_

All capacitive circuits have some amount of resistance. AC current will lead somewhere between a purely resistive circuit and a purely capacitive circuit. The exact amount of lead depends on the ratio of resistance and capacitive reactance. The more resistive a circuit is, the closer it is to being in phase. The more capacitive a circuit is, the more out of phase it is. In the following illustration, resistance and capacitive reactance are equal. Current leads voltage by 45 degrees. 45 Degrees

XC = 10 Ω

+ Voltage Current 0 R = 10 Ω _

Calculating Impedance in a Capacitive Circuit

The following formula is used to calculate impedance in a capacitive circuit: Z = R2 + XC2

In the circuit illustrated above, resistance and capacitive re tance are each 10 ohms. Impedance is 14.1421 ohms. Z = 102 + 102 Z=

200

Z = 14.1421 Ω

65

The following vector illustrates the relationship between resistance and capacitive reactance of a circuit containing equal values of each. The angle between the vectors is the phase angle represented by the symbol θ. When capacitive reactance is equal to resistance the resultant angle is -45 degrees. It is this angle that determines how much current will lead voltage. R = 10 Ω

θ Z = 2 .14 14

XC = 10 Ω

1 Ω

Review 9 1.

In a circuit containing inductance, capacitance, or both, opposition to current flow is called ____________ .

2.

Total opposition to current flow in a circuit that contains both reactance and resistance is called ____________ .

3.

In a 50 hertz circuit, containing a 10 mh inductor, the inductive reactance is ____________ ohms.

4.

In a purely inductive circuit, ____________ a. current and voltage are in phase b. current leads voltage by 90 degrees c. current lags voltage by 90 degrees

5.

In a purely capacitive circuit, ____________ a. current and voltage are in phase b. current leads voltage by 90 degrees c. current lags voltage by 90 degrees

66

6.

In a 50 hertz circuit, containing a 10 microfarad capacitor, the capacitive reactance is ____________ ohms.

7.

In a circuit with 5 Ω resistance, and 10 Ω inductive reactance, impedance is ____________ ohms.

8.

In a circuit with 5 Ω resistance, and 4 Ω capacitive reactance, impedance is ____________ ohms.

Series R-L-C Circuit

Circuits often contain elements of resistance, inductance, and capacitance. In an inductive AC circuit, current lags voltage by 90 degrees. In a AC capacitive circuit, current leads voltage by 90 degrees. It can be seen that inductance and capacitance are 180 degrees apart. Since they are 180 degrees apart, one element will cancel out all or part of the other element.

XL

XC

R

An AC circuit is: • • • Calculating Total Impedance in a Series R-L-C Circuit

Resistive if XL and XC are equal Inductive if XL is greater than XC Capacitive if XC is greater than XL

The following formula is used to calculate total impedance of a circuit containing resistance, capacitance, and inductance: Z = R2 + (XL - XC)2

In the case where inductive reactance is greater than capacitive reactance, subtracting XC from XL results in a positive number. The positive phase angle is an indicator that the net circuit reactance is inductive, and current lags voltage. In the case where capacitive reactance is greater than inductive reactance, subtracting XC from XL results in a negative number. The negative phase angle is an indicator that the net circuit reactance is capacitive and current leads voltage. In either case, the value squared will result in positive number.

67

Calculating Reactance and Impedance in a Series R-L-C Circuit

In the following 120 volt, 60 hertz circuit, resistance is 1000 Ω, inductance is 5 mh, and capacitance is 2 µF. To calculate total impedance, first calculate the value of XL and XC, then impedance can be calculated.

R = 1000 Ω

L = 5 mh

C = 2 µF

XL = 2πfL XL = 6.28 x 60 x 0.005 XL = 1.884 Ω 1 XC = 2πfC 1 XC = 6.28 x 60 x 0.000002 XC = 1,327 Ω

Z = R2 + (XL - XC)2 Z = 10002 + (1.884 - 1,327)2 Z = 1,000,000 + ( - 1,325.116)2 Z = 1,000,000 + 1,755,932.41 Z = 2,755,932.41 Z = 1,660.1 Ω

Calculating Circuit Current in a Series R-L-C Circuit

Ohm’s Law can be applied to calculate total circuit current. I= E Z I=

120 1,660.1

I = 0.072 Amps

68

Parallel R-L-C Circuit

Calculating Impedance in a Parallel R-L-C Circuit

Total impedance (Zt) can be calculated in a parallel R-L-C circuit if values of resistance and reactance are known. One method of calculating impedance involves first calculating total current, then using the following formula: E Zt = t It

Total current is the vector sum of current flowing through the resistance plus, the difference between inductive current and capacitive current. This is expressed in the following formula: It =

IR2 + (IC - IL)2

In the following 120 volt, 60 hertz circuit, capacitive reactance has been calculated to be 25 Ω and inductive reactance 50 Ω. Resistance is 1000 Ω. A simple application of Ohm’s Law will find the branch currents. Remember, voltage is constant throughout a parallel circuit.

R = 1000 Ω

XL = 50 Ω

XC = 25 Ω

IR =

E R

E IL = XL

E IC = XC

IR =

120 1000

120 IL = 50

120 IL = 25

IL = 2.4 Amps

IL = 4.8 Amps

IR = 0.12 Amps

69

Once the branch currents are known, total current can be calculated. It =

IR2 + (IC - IL)2

It =

0.122 + (4.8 - 2.4)2

It =

0.0144 + 5.76

It =

5.7744

It = 2.4 Amps

Impedance is now found with an application of Ohm’s Law. E Zt = t It Zt =

120 2.4

Zt = 50 Ω

70

Power and Power Factor in an AC Circuit

Power consumed by a resistor is dissipated in heat and not returned to the source. This is true power. True power is the rate at which energy is used. Current in an AC circuit rises to peak values and diminishes to zero many times a second. The energy stored in the magnetic field of an inductor, or plates of a capacitor, is returned to the source when current changes direction. Although reactive components do not consume energy, they do increase the amount of energy that must be generated to do the same amount of work. The rate at which this non-working energy must be generated is called reactive power. Power in an AC circuit is the vector sum of true power and reactive power. This is called apparent power. True power is equal to apparent power in a purely resistive circuit because voltage and current are in phase. voltage and current are also in phase in a circuit containing equal values of inductive reactance and capacitive reactance. If voltage and current are 90 degrees out of phase, as would be in a purely capacitive or purely inductive circuit, the average value of true power is equal to zero. There are high positive and negative peak values of power, but when added together the result is zero. True Power and Apparent Power Formulas

The formula for apparent power is: P = EI

Apparent power is measured in volt-amps (VA). True power is calculated from another trigonometric function, the cosine of the phase angle (cos θ). The formula for true power is: P = EI cos θ

True power is measured in watts.

71

In a purely resistive circuit, current and voltage are in phase. There is a zero degree angle displacement between current and voltage. The cosine of zero is one. Multiplying a value by one does not change the value. In a purely resistive circuit the cosine of the angle is ignored. In a purely reactive circuit, either inductive or capacitive, current and voltage are 90 degrees out of phase. The cosine of 90 degrees is zero. Multiplying a value times zero results in a zero product. No power is consumed in a purely reactive circuit. Calculating Apparent Power in a simple R-L-C Circuit

In the following 120 volt circuit, current is equal to 84.9 milliamps. Inductive reactance is 100 Ω and capacitive reactance is 1100 Ω. The phase angle is -45 degrees. By referring to a trigonometric table, the cosine of -45 degrees is found to be .7071.

R = 1000 Ω XL = 100 Ω XC = 1100 Ω 120 VAC

The apparent power consumed by the circuit is: P = EI P = 120 x 0.0849 P = 10.2 VA

The true power consumed by the circuit is: P = EI cos θ P = 120 x 0.0849 x 0.7071 P = 7.2 Watts

Another formula for true power is: P = I2R P = 0.08492 x 1000 P = 7.2 Watts

72

Power Factor

Power factor is the ratio of true power to apparent power in an AC circuit. Power factor is expressed in the following formula: PF =

True Power Apparent Power

Power factor can also be expressed using the formulas for true power and apparent power. The value of EI cancels out because it is the same in the numerator and denominator. Power factor is the cosine of the angle. PF =

EI cos θ EI

PF = cos θ

In a purely resistive circuit, where current and voltage are in phase, there is no angle of displacement between current and voltage. The cosine of a zero degree angle is one. The power factor is one. This means that all energy delivered by the source is consumed by the circuit and dissipated in the form of heat. In a purely reactive circuit, voltage and current are 90 degrees apart. The cosine of a 90 degree angle is zero. The power factor is zero. This means the circuit returns all energy it receives from the source to the source. In a circuit where reactance and resistance are equal, voltage and current are displaced by 45 degrees. The cosine of a 45 degree angle is .7071. The power factor is .7071. This means the circuit uses approximately 70% of the energy supplied by the source and returns approximately 30%.

73

Review 10 1.

An AC circuit is ____________ if inductive reactance and capacitive reactance are equal.

2.

A series AC circuit is ____________ if there is more inductive reactance than capacitive reactance.

3.

A series AC circuit is ____________ if there is more capacitive reactance than inductive reactance.

4.

In a 120 VAC, 60 hertz series circuit, with 1000 Ω of resistance, 10 mh of inductance and 4 µF of capacitance, impedance is ____________ Ω and current is ____________ amps.

5.

In the illustrated circuit,

R = 1000 Ω XL = 200 Ω XC = 1000 Ω 120 VAC 60 Hz

It is __________ amps, and impedance is __________ Ω.

74

6.

True power is measured in ____________ .

7.

A circuit with 0.2 amps flowing through 100 Ω of resistance, is consuming ____________ watts.

Transformers

Mutual Induction

Transformers are electromagnetic devices that transfer electrical energy from one circuit to another by mutual induction. Mutual induction is the coupling of inductances by their mutual magnetic fields. In a single-phase transformer there are two coils, a primary and a secondary coil. The following circuit illustrates mutual induction. The AC generator provides electrical power to the primary coil. The magnetic field produced by the primary induces a voltage into the secondary coil, which supplies power to a load.

Primary Coil

Secondary Coil

Transformers are used to step a voltage up to a higher level, or down to a lower level. Transformers are used extensively in power distribution systems, allowing power companies to transfer electrical energy many miles. Power generators typically generate high voltages. This voltage varies, depending on the generator, but a typical voltage might be 15 KV. The voltage is stepped up through a transformer to higher levels for transmission to substations. Typical voltages range from 115 KV to 765 KV. The electrical power is received at substation transformers many miles away where it is stepped down. Typical voltage might be 34 KV or 69 KV. From here, electrical power is fed to a distribution substation. It can also be fed directly to factory locations. If the power is fed to a factory, transformers at the factory site reduce the voltage to usable levels. The power fed to a distribution substation is reduced by transformers at the substation for factory and home use.

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Coefficient of Coupling

Mutual inductance between two coils depends on their flux linkage. Maximum coupling occurs when all the lines of flux from the primary coil cut through the secondary winding. The amount of coupling which takes place is referred to as coefficient of coupling. To maximize coefficient of coupling, both coils are often wound on an iron core which is used to provide a path for the lines of flux. The following discussion of step-up and step-down transformers applies to transers with an iron core.

Lines of Flux Confined to Iron Core

Lines of Flux that don’t Couple

Voltage, Current, and the Number of Turns in a Coil

There is a direct relationship between voltage, impedance, current, and the number of coil turns in a transformer. This relationship can be used to find either primary or secondary voltage, current, and the number of turns in each coil. It is the number of turns which determine if a transformer is a step up or step down transformer. The following “rules-of-thumb” apply to transformers: •

If the primary coil has fewer turns than the secondary coil, it is a step-up transformer.

•

If the primary coil has more turns than the secondary coil, it is a step-down transformer.

When the number of turns on the primary and seconday coils of a transformer are equal, input voltage, impedance, and current are equal to output voltage, impedance, and current.

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Step-Up Transformer

A step-up transformer is used when it is desirable to step voltage up in value. The following circuit illustrates a stepup transformer. The primary coil has fewer turns than the secondary coil. The number of turns in a transformer is given as a ratio. When the primary has fewer turns than the secondary, voltage and impedance are stepped up. In the circuit illustrated, voltage is stepped up from 120 VAC to 240 VAC. Because impedance is also stepped up, current is stepped down from 10 amps to 5 amps. 1:2

Primary Coil 900 Turns

Secondary Coil 1800 Turns

120 VAC Supply 10 Amps

Step-Down Transformer

240 VAC 5 Amps

A step-down transformer is used when it is desirable to step voltage down in value. The following circuit illustrates a step-down transformer. The primary coil has more turns than the secondary coil. The step-down ratio is 2:1. voltage and impedance are stepped down, current is stepped up. 2:1

Primary Coil 1800 Turns

240 VAC Supply 5 Amps

Seconday Coil 900 Turns

120 VAC Out 10 Amps

77

Single-Phase Transformer

120 or 240 VAC single-phase transformers are used to supply lighting, receptacle, and small appliance loads. A transformer with a 240 VAC secondary can be used to supply 240 VAC to larger appliances such as stoves, air conditioners and heaters. A 240 VAC secondary can be tapped in the center to provide two sources of 120 VAC power. Primary

Primary

120 VAC

120 VAC

240 VAC

Secondary

Formulas for Calculating the Number of Primary and Secondary Turns of a Transformer

Ground

Secondary

There are a number of useful formulas for calculating, voltage, current, and the number of turns between the primary and secondary of a transformer. These formulas can be used with either step-up or step-down transformers. The following legend applies to the transformer formulas: ES EP IS IP NS NP

= = = = = =

secondary voltage primary voltage secondary current primary current turns in the secondary coil turns in the primary coil

To find voltage: ES =

EP x IP IS

EP =

ES x IS IP

IP =

ES x IS EP

To find current: IS =

EP x IP ES

To find the number of coil turns: NS =

78

120 VAC

ES x NP EP

NP =

EP x NS ES

Using the values for the step-down transformer in the example of the previous page, the secondary voltage can be verified. ES =

EP x IP IS

ES =

240 Volts x 5 Amps 10 Amps

ES =

1200 10

ES = 120 Volts

Transformer Ratings

Transformers are rated in kVA (kilovolt-amps). This rating is used rather than watts because loads are not purely resistive. Only resistive loads are measured in watts. The kVA rating determines the current a transformer can deliver to its load without overheating. Given volts and amps, kVA can be calculated. Given kVA and volts, amps can be calculated. kVA =

Volts x Amps 1000

Amps =

kVA x 1000 Volts

Using the illustrated step-down transformer, the kVA rating can be calculated. The kVA rating of a transformer is the same for both the primary and the secondary. Primary kVA =

240 x 5 1000

Primary kVA = 1.2 kVA Secondary kVA =

120 x 10 1000

Secondary kVA = 1.2 kVA

Transformer Losses

Most of the electrical energy provided to the primary of a transformer is transferred to the secondary. Some energy, however, is lost in heat in the wiring or the core. Some losses in the core can be reduced by building the core of a number of flat sections called laminations.

79

Three-Phase Transformers

Delta Connections

Three-phase transformers are used when three-phase power is required for larger loads such as industrial motors. There are two basic three-phase transformer connections, delta and wye. Delta transformers are used where the distance from the supply to the load is short. A delta is like three singlephase transformers connected together. The secondary of a delta transformer is illustrated below. For simplicity, only the secondary of a three-phase transformer is shown. The voltages shown on the illustration are secondary voltages available to the load. Delta transformers are schematically drawn in a triangle. The voltages across each winding of the delta triangle represents one phase of a three phase system. The voltage is always the same between any two wires. A single phase (L1 to L2) can be used to supply single phase loads. All three phases are used to supply three phase loads. L1

480 Volts

480 Volts

480 Volts

L2 480 Volts 480 Volts

L3

L1 to L2 = 480 volts L2 to L3 = 480 volts L1 to L3 = 480 volts

80

Balanced Delta Current

When current is the same in all three coils, it is said to be balanced. In each phase, current has two paths to follow. For example, current flowing from L1 to the connection point at the top of the delta can flow down through one coil to L2, and down through another coil to L3. When current is balanced, coil current is 58% of the line current measured on each phase. If the line current is 50 amps on each phase, coil current would be 29 amps.

29 Amps

50 Amps

L1

50 Amps

L3

29 Amps

50 Amps

L2

29 Amps

Unbalanced Delta Current

When current is different in all three coils, it is unbalanced. The following diagram depicts an unbalanced system. 43.6 Amps Coil A 30 Amps

L1

Coil B 20 Amps

26.4 Amps

L2

Coil C 10 Amps

36 Amps

L3

Though current is usually measured with an ammeter, line cur rent of an unbalanced delta transformer can be calculated with the following formulas: IL1 =

IA2 + IB2 + (IA x IB)

IL2 =

IB2 + IC2 + (IB x IC)

IL3 =

IA2 + IC2 + (IA x IC)

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Wye Connections

The wye connection is also known as a star connection. Three transformers are connected to form a “Y” shape. The wye transformer secondary, (shown below) has four leads, three phase connectors, and one neutral. The voltage across any phase (line-to-neutral) will always be less than the line-to-line voltage. The line-to-line voltage is 1.732 times the line-to-neutral voltage. In the circuit below, line-to-neutral voltage is 277 volts. Line-to-line voltage will be 480 volts (277 x 1.732). L1

480 Volts 277 Volts L2

277 Volts

N

480 Volts

480 Volts

277 Volts

L3

Review 11

82

1.

If the primary of a transformer has more turns than the secondary, it is a ____________ transformer.

2.

If the primary of a transformer has fewer turns than the secondary, it is a ____________ transformer.

3.

The secondary voltage of an iron-core transformer with 240 volts on the primary, 40 amps on the primary, and 20 amps on the secondary is ____________ volts.

4.

A transformer with a 480 volt, 10 amp primary, and a 240 volt, 20 amp secondary will be rated for ____________ kVA.

5.

A wye connected, three-phase transformer secondary, with 240 volts line-to-line will have ____________ volts line-to-neutral.

Review Answers

Review 1

1) electron (-), proton (+), neutron (neutral); 2) free electrons; 3) many; 4) a, c, e, g; 5) many, few.

Review 2

1) electrons; 2) negative; 3) positive; 4) repel, attract; 5) voltage; 6) b; 7) a.

Review 3

R ; 2) amps, volts, ohms; 3) .5 amps; 4) 45 Ω; 5) 2 amps; 1) 6) 6 volts, 6 volts; 7) 20 volts, 80 volts.

Review 4

1) 5 Ω; 2) 5.45 Ω; 3) 3.33 Ω; 4) 12 volts; 5) 6 amps; 6) 2.4 amps, 1.6 amps.

Review 5

1) 12 Ω, 22 Ω; 2) 40 Ω, 13.33 Ω.

Review 6

1) power; 2) P = E x I; 3) 36 watts; 4) iron, north-south; 5)north, south; 6) left, thumb, lines of flux.

Review 7

1) sine wave; 2) 120 degrees; 3) one; 4) -129.9 volts; 5) 106.05 volts rms.

Review 8

1) 10 mh; 2) 2.5 mh; 3) 2.5 µF; 4) 25 µF.

Review 9

1) reactance; 2) impedance; 3) 3.14 Ω; 4) c; 5) b; 6) 318.5 Ω; 7) 11.18 Ω; 8) 6.4 Ω.

Review 10

1) resistive; 2) inductive; 3) capacitive; 4) 1198 Ω, .1 amp; 5) 84.9 milliamps,1414.2 Ω; 6) watts; 7) 4 watts;

Review 11

1) step-down; 2) step-up; 3) 480 volts; 4) 4.8 kVA; 5) 138.56 volts.

I=

E

83

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. After completing the test, mail the answer sheet in for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. Questions

1.

A material that is a good insulator is a. b.

2.

a. b. 4.

negative charge positive charge

2 amps 5 amps

c. d.

neutral charge no charge

c. d.

0.2 amps 0.5 amps

The total resistance in a series circuit containing three, 10 Ω, resistors is 10 Ω 30 Ω

c. d.

3.33 Ω 100 Ω

In a 12 volt series circuit where R1=10 Ω, R2=20 Ω, and R3=10 Ω, current flow through R2 is a. b.

84

silver rubber

In a simple electric circuit with a 12 volt supply, and a 24 Ω resistor, current is

a. b. 5.

c. d.

A material with more protons than electrons has a a. b.

3.

copper aluminum

0.3 amps 0.5 amps

c. d.

0.25 amps 3.33 amps

6.

In a circuit containing three 30 Ω resistors in parallel, the total resistance is a. b.

7.

a. b. 12.

efficiency power factor

3 amps 3 watts

c. d.

48 amps 48 watts

415.7 volts 480 volts

c. d.

240 volts 0 volts

415.7 volts 339.4 volts

c. d.

480 volts 679 volts

The time constant of a series circuit with a 10 mh inductor, and a 5 Ω resistor is 2 milliseconds 2 seconds

c. d.

2 microseconds .5 seconds

The total inductance of a series circuit containing three inductors with values of 10mh, 20 mh, and 40 mh is a. b.

13.

c. d.

The effective voltage of an AC sine wave whose peak voltage is 480 volts is a. b.

11.

energy power

The instantaneous voltage at 150 degrees of an AC sine wave whose peak voltage is 480 volts is a. b.

10.

10 Ω 0.1 Ω

Power in a simple 12 volt, 4 amp series circuit is a. b.

9.

c. d.

The rate at which work is done is called a. b.

8.

30 Ω 90 Ω

5.7 pF 5.7 mh

c. d.

70 Ω 70 mh

The time constant for a series circuit with a 20 Ω resistor and a 4 µF capacitor is a. b.

80 microseconds 80 milliseconds

c. d.

5 microseconds 5 milliseconds

85

14.

Total capacitance for a series circuit containing a 2 µF, 4 µF, and 8 µF capacitors is a. b.

15.

1.884 Ω 1884 Ω

c. d.

0.0005 Ω 0.05 Ω

current leads voltage by 90 degrees current lags voltage by 90 degrees current and voltage are in phase current leads voltage by 30 degrees

30 Ω 10 Ω

c. d.

14.1 Ω 22.4 Ω

inductive resistive

c. d.

capacitive in phase

An iron-core transformer with 120 volt, 10 amp primary, and 5 amp secondary is a a. b. c. d.

86

impedance capacitance

A series AC circuit containing more capacitive reactance than inductive reactance is a. b.

20.

c. d.

In a series AC circuit with a 20 Ω resistor and a 10 Ω inductive reactance, impedance is a. b.

19.

resistance reactance

In a purely inductive circuit a. b. c. d.

18.

1.14 µF 4 µF

In a 60 hertz circuit containing 5 millihenrys of inductance, inductive reactance is a. b.

17.

c. d.

Total opposition to current flow in an AC circuit that contains both reactance and resistance is called a. b.

16.

14 µF 0.875 µF

step down transformer with a 60 volt secondary step up transformer with a 240 volt secondary step up transformer with a 480 volt secondary step down transformer with a 30 volt secondary

87


quickSTEP online courses are available at http://www.sea.siemens.com/step. The quickSTEP training site is divided into three sections: Courses, Downloads, and a Glossary. Online courses include reviews, a final exam, the ability to print a certificate of completion, and the opportunity to register in the Sales & Distributor training database to maintain a record of your accomplishments. From this site the complete text of all STEP courses can be downloaded in PDF format. These files contain the most recent changes and updates to the STEP courses. A unique feature of the quickSTEP site is our pictorial glossary. The pictorial glossary can be accessed from anywhere within a quickSTEP course. This enables the student to look up an unfamiliar word without leaving the current work area.

88

Table of Contents

Introduction ..............................................................................2 Siemens Energy & Automation, Inc..........................................4 Electric Power...........................................................................6 Residential Applications.......................................................... 11 Commercial Applications ........................................................20 Industrial Applications.............................................................36 Manufacturing Applications ....................................................47 Discrete Parts Manufacturing .................................................49 Assembly Processes ..............................................................56 Batch and Continuous Processes ...........................................64 Pictorial Glossary ....................................................................70 Review Answers................................................................... 118 Final Exam ............................................................................ 119

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Basics of Electrical Products. Upon completion of Basics of Electrical Products, you should be able to:

2

•

Explain how power is distributed from a power distribution plant to various residential, commercial, and industrial facilities

•

Explain how Siemens products are used in basic residential, commercial, and industrial applications

•

Explain the similarities and differences between load centers, panelboards, switchboards, switchgear, and secondary unit substations

•

Identify various Siemens products used in discrete parts manufacturing, assembly, batch processing, and continuous processing

•

Identify various Siemens products by trade name

This knowledge will help you better understand customer applications. In addition, you will be better prepared to discuss electrical products and systems with customers. You should complete Basics of Electricity before attempting Basics of Electrical Products. Once you have completed Basics of Electrical Products, you should complete or review any of the other STEP 2000 courses that are relevant to your work. The general information provided in Basics of Electrical Products will help you better understand the specific product details in the remaining STEP 2000 courses. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. EQ, instabus, WinCC, SITOP, SINUMERIK, SIMODRIVE, SIMOREG, and SIMATIC are registered trademarks of Siemens Energy & Automation, Inc. Uni-Pak, Sentron, ACCESS, Super Blue Pennant, Medallion, ESP100, INNOVA PLUS, System 89, and PCS are trademarks of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-2002, National Electrical Code Copyright, 2001, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories Inc. and UL are registered trademarks of Underwriters Laboratories Inc., Northborook, IL 60062. National Electrical Manufacturers Association is located at 2101 L Street, N.W., Washington, D.C. 20037. The abbreviation “NEMA” is understood to mean National Electrical Manufacturers Association. MS-DOS, Windows, and Windows NT are registered trademarks of Microsoft, Inc. Other trademarks are the property of their respective owners.

3

Siemens Energy & Automation, Inc.

Company Overview

Siemens Energy & Automation (SE&A) is one of a number of companies owned by Siemens AG. Siemens AG has its headquarters in Munich, Germany, and is one of the world’s largest suppliers of electrical and electronic products, systems, and associated services. Siemens companies operate in the United States under the financial umbrella of Siemens Corporation. These companies sell equipment for use in a vast array of industries and applications. SE&A sells a broad range of products that are used in residential, commercial, and industrial applications. A generic listing of the products sold by SE&A sales force and authorized distributors is shown below. • • • • • • • • • • • • • • • • • • • • • • •

4

AC Motors, Pumps, and Compressors Busway Circuit Breakers Control Components Safety Switches Human Machine Interfaces (HMI) Industrial Networks Industrial Personal Computers Load Centers Metering Motion Controls and Servo Drives Motor Control Centers Panelboards Power Monitoring and Management Systems Power Supplies Process Automation Systems Programmable Logic Controllers (PLCs) Radio Frequency Identification System Software Solutions Switchboards Switchgear Transformers Variable Speed Drives

Key to Understanding SE&A Products

Depending upon your experience with electrical and electronic products, you may find the generic listing to be either unintelligible or straightforward. When this list is expanded into the literally thousands of specific products sold by SE&A, even the most experienced professionals may be dazed by the seeming complexity. As diverse as this product listing would be, however, there are some common concepts. •

These products use electrical power and, in many cases, control the flow of energy to other products or systems.

•

These products are most commonly used in residential, commercial, and industrial applications.

In order to help you better understand SE&A products, this course will look at where many of these products fit in the flow of energy in sample residential, commercial, and industrial applications. The flow of energy from the electric utility will be discussed only briefly; however, keep in mind that many of the products listed above are also used by electric utilities. In addition, the products of other Siemens companies, especially Siemens Westinghouse Power Corporation and Siemens Power Transmission & Distribution, are used extensively by these utilities. By better understanding where electrical products fit in the flow of energy, you can better understand the physical and electrical requirements of these products.

5

Electric Power

Power, originating at a power generating plant, is distributed to residential, commercial, and industrial customers through various transmission lines and substations.

6

Power Sources

There are several sources used to produce power. Coal, oil, and uranium are fuels used to convert water into steam which in turn drives a turbine. Some utilities also use gas turbines, or both gas and steam turbines, for combined cycle operation. The output shaft of the turbine is connected to an AC generator. The AC generator is rotated by the turbine. It is the AC generator which converts the mechanical energy into electrical energy.

Hydroelectric Power

Hydroelectric power plants use mechanical energy from falling water to turn the turbine.

7

AC Generators

AC generators operate on the theory of electromagnetic induction. This simply means that when conductors are moved through a magnetic field a voltage is induced into the conductors. A basic generator consists of a magnetic field, an armature, slip rings, brushes, and some type of resistive load. An armature is any number of conductive wires (conductors) wound in loops which rotate through the magnetic field. For simplicity, one loop is shown.

If the rotation of the AC generator were tracked through a complete revolution of 360°, it could be seen that during the first quarter of a revolution voltage would increase until it reached a maximum positive value at 90°. Voltage would decrease during the second quarter of a revolution until it reached zero at 180°. During the third quarter of a revolution, voltage would increase in the opposite direction until it reached a maximum negative value at 270°. During the last quarter of a revolution, voltage would decrease until it reached zero at 360°. This is one complete cycle or one complete alternation between positive and negative. If the armature of the AC generator were rotated 3600 times per minute (RPM) we would get 60 cycles of voltage per second, or 60 hertz.

8

Energy Transfer

The role of the generator just described is to change mechanical energy into electrical energy. In order for this energy to be useful, however, it must be transmitted to the utility’s customers via transmission lines. The most efficient way to do this is to increase the voltage while at the same time reducing the current. This is necessary to minimize the energy lost in heat on the transmission lines. These losses are referred to as 2 I R (I-squared-R) losses since they are equal to the square of the current times the resistance of the power lines. Once the electrical energy gets near the end user, the utility will need to step down the voltage to the level needed by the user.

Transformers

The device that utilities use to step up the voltage at the generator end and step down the voltage at the user end is called a transformer. The transformer transfers energy from a primary coil to a secondary coil by mutual induction. The AC generator provides electrical power to the primary coil. The magnetic field produced by the primary coil induces a voltage into the secondary coil which supplies power to the connected load. The load in this case would be the entire electrical distribution network including all residential, commercial, and industrial customers. A step-up transformer is used when it is desirable to step voltage up from one level to another. A 1:2 step-up transformer, for example, would be used to step 120 volts up to 240 volts. A 2:1 step-down transformer would be used to step 240 volts down to 120 volts.

9

Three-Phase Voltage

For simplicity, the generator and transformers shown so far have been single-phase devices. While single-phase power is needed for many applications, utilities generate and transmit three-phase power. In a three-phase system, the generator produces three voltages. Each voltage phase rises and falls at the same frequency (60 Hz in the U.S., 50 Hz in many other countries); however, the phases are offset from each other by 120°.

Three-Phase Transformers

Transformers used with three-phase power require three interconnected coils in both the primary and the secondary. These transformers can be connected in either a wye or a delta configuration. The type of transformer and the actual voltage depend on the requirements and capability of the power company and the needs of the customer. The following illustration shows the secondary of a wyeconnected transformer and the secondary of a delta-connected transformer.

10

Residential Applications

Power, generated at a power plant, then stepped up to a high transmission voltage is brought to a local substation. Here, it is stepped down to a lower distribution voltage. When it reaches its final destination at a residential customer, it is stepped down to 240 volts. Only single-phase power is used in a typical residential application.

11

Power Supply

The most common supply system used in residential applications today is a single-phase, three-wire supply system. In this system, there are 120 volts between either hot wire and neutral and 240 volts between the two hot wires. The 120-volt supply is used for general-purpose receptacles and lighting. The 240 volt supply is used for heating, cooling, cooking, and other high-demand loads.

Service Entrance

Power, purchased from a utility company, enters the house through a metering device and connects to a load center. This is the service entrance. Residential service can come from an overhead utility transformer or from a lateral service run underground.

12

Meter Sockets

Most of us are familiar with the watt-hour meter located outside our homes. The watt-hour meter is used by the power company to determine how much electricity has been consumed for billing purposes. Siemens manufactures single-position meter sockets for residential use.

Meter Mains and Meter Combinations

Meter mains and meter combinations are similar. Meter mains incorporate space for a watt-hour meter (supplied by the utility company) and a main service disconnect within the same enclosure. Meter combinations incorporate space for a watthour meter and circuit breaker space for electrical distribution in a residence. These types of load centers are also used as trailer service panels. Meter combinations are primarily found on the West Coast but are also becoming popular in other areas of the country.

13

Modular Meter Centers Metering Systems

Modular meter centers are used for multi-family dwellings such as duplexes or apartment buildings. These are used in conjunction with Siemens load centers. Modular meter centers are available with two to six meter compartments. Metering systems are another option for multi-family dwellings. These are self-contained systems with two to six meter compartments. Individual branch circuit breakers for tenants are located in a separate compartment adjacent to the meter socket.

Distribution

14

The incoming power then goes to a load center which provides circuit control and overcurrent protection. The power is distributed from the load center to various branch circuits for lighting, appliances, and electrical outlets.

Load Centers

The term load center is an industry term used to identify a panelboard used in certain applications. Load centers are typically rated 225 amps or less and 240 volts maximum and are intended for use in residential applications. A typical load center consists of an enclosure, interior, and trim. Circuit breakers are mounted in the interior to provide circuit protection and control for light, heat, and power circuits.

Circuit Breakers

Circuit breakers provide a manual means of energizing and de-energizing a circuit. In addition, circuit breakers provide automatic overcurrent protection of a circuit. Siemens residential circuit breakers are available with current ratings from 15-125 amps and a voltage rating of 120/240 volts. In residential applications, single-pole breakers protect 120 volt circuits; two-pole breakers protect 240 volt circuits.

15

Circuit Breaker/ Surge Arrester

Siemens manufactures special types of circuit breakers for load center use. The Siemens circuit breaker/surge arrester mounts in a load center similarly to a conventional circuit breaker. This device protects electronic equipment, such as televisions or computers, from electrical surges on the system. Surges can come from electrical equipment, switching, or lightning.

GFCI Circuit Breaker

The ground fault circuit interrupter (GFCI) is required on certain residential receptacles, such as bathroom receptacles, receptacles located within six feet of a kitchen sink, and outdoor receptacles. The GFCI is designed to interrupt a circuit when a ground fault occurs. Often the GFCI is mounted at the receptacle. When this is not feasible, a Siemens GFCI circuit breaker is installed in the load center.

16

AFCI Circuit Breaker

GFCI devices are designed to protect a person from getting a shock when touching an ungrounded appliance. Arc Fault Circuit Interrupters (AFCI), in comparison, protect against a fire being started from an unintended arc. An arc fault occurs when a current-carrying conductor has an arching condition to ground or another conductor. An AFCI device is intended to provide protection from the effects of arc faults by recognizing the characteristics unique to arcing and de-energizing the circuit when an arc fault is detected. The arc generated will cause the AFCI to trip. Arcs normally generated from electric equipment such as a light switch or power drill will not cause the AFCI to trip. Arc-Fault Circuit Interrupter protection was first introduced in the 1999 National Electrical Code®. NEC® Article 210.12 and has an effective date of 2002. This requirement applies to all branch circuits that supply 125-volt, single-phase, 15- and 20-amp receptacle outlets installed in dwelling unit bedrooms.


17

Enclosed Circuit Breakers and Disconnects

Siemens also manufactures circuit breaker enclosures and fused, non-fused, and molded case switch disconnects.

Enclosed circuit breakers and disconnects provide a convenient means of disconnecting power to allow for the service of equipment such as an air conditioner located downstream from a service entrance load center.

18

Review 1 1.

A ____________ is a device that converts mechanical energy into electrical energy.

2.

A transformer that increases the voltage from primary to secondary is called a ____________ transformer.

3.

Phases are offset by ____________ degrees in a threephase system.

4.

____________ volts is used for general-purpose receptacles and lighting in residential applications.

5.

____________ is a type of electrical service that is run underground.

6.

Modular meter centers can be supplied with two to ____________ meter compartments.

7.

The circuit breaker/ ____________ ____________ is a type of circuit breaker manufactured by Siemens that protects electronic equipment from electrical surges.

8.

A ____________ is required on certain residential receptacles such as bathroom receptacles and receptacles located within six feet of a kitchen sink.

19

Commercial Applications

Commercial applications range from small offices and stores to larger complexes such as hotels, restaurants, office buildings, and shopping malls. A small, single-tenant office building, for example, would not have a large demand for power. In this case, all that may be required is a single-position meter socket and panelboard. Small-demand, multiple-tenant applications, such as found in a small strip mall, might also have a low demand for electrical power. In these cases, metering systems or modular meter centers, as discussed in the “Residential Applications” section, might satisfy the load requirements. Typically, commercial applications have higher demands for electrical power than residential applications. Electricity is used in commercial applications for heating, cooling, and lighting on a much larger scale. Some commercial applications may also operate machinery such as elevators and small conveyors.

20

Busway

There are two methods to route power into a building or distribute power throughout a building. Electrical cable can be run inside conduit or busway can be used. The distribution system in a building frequently consists of a combination of busway and cable and conduit.

NEMA Definition

Busway, as defined by the National Electrical Manufacturers Association (NEMA), is a prefabricated electrical distribution system consisting of bus bars in a protective enclosure, including straight lengths, fittings, devices, and accessories. Bus bars are the electrical conductors that carry power. The bars are individually insulated and enclosed in a housing. Siemens Sentron busway is illustrated below.

21

Service Entrance

Outdoor feeder busway is often used as service entrance conductors to bring power into a switchboard or panelboard. This may involve routing power from outside the building or from a transformer vault inside the building. For distribution inside the building indoor feeder or plug-in busway can be used.

Busway Used in a Distribution System

A major advantage of busway is the ease in which busway sections are connected together. Electrical power can be supplied to any area of a building by connecting standard lengths of busway. It typically takes fewer man-hours to install or change a busway system than cable and conduit assemblies. Savings of 25 to 30% of the total installation cost are common when busway is used. Busway risers (vertical busway) can be installed economically in a high-rise building, such as the one illustrated below, where it can be used to distribute power to lighting and air-conditioning loads.

22

Power Distribution in Commercial Applications

Panelboards and switchboards can be used in commercial applications as service entrance equipment and for distribution of electrical power throughout the building. Although load centers, panelboards, and switchboards are similar in function and appearance, they are different products and designed to meet different needs. The following table shows how load centers, panelboards, and switchboards are defined. The National Electrical Code® (NEC®) makes no distinction between a load center and a panelboard.

Panelboard Construction

Panelboards are constructed in a similar manner as load centers. Panelboards are more robust and able to handle the more demanding loads of commercial applications.


23

Panelboards

Siemens manufactures a variety of panelboards to meet various distribution requirements. P1, SE, and S3 lighting and power panelboards are smaller in size and well suited to demands of commercial applications. P1 panelboards handle loads up to 400 amps. SE and S3 panelboards handle loads up to 600 amps. S4, S5, F1, and F2 power panelboards are designed for power applications up to 1200 amps.

Switchboard Construction

Switchboards typically consist of a service section and one or more distribution sections. The service section can be fed directly from the utility transformer. In addition to the main disconnect, the service section usually contains utility or customer metering provisions.

24

SB1, SB2, SB3

Siemens manufactures a variety of switchboards. The type of switchboard selected is determined by a variety of factors such as space, load, and environment. Sentron SB1, SB2, and SB3 are selected when space is a consideration. These switchboards are accessed from the front and most can be mounted against a wall. SB1, SB2, and SB3 switchboards can be found in a variety of commercial, institutional, and industrial buildings.

RCIII Switchboards

RCIII switchboards are rear connected and require rear access and are typically found in industrial applications.

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Super Blue Pennant

The Super Blue Pennant™ switchboard is designed as a service entrance switchboard. The main service disconnect and distribution devices are contained in a single unit. Super Blue Pennant switchboards are rated for 400, 600, or 800 amps.

Commercial Metering

Commercial metering switchboards are designed for Switchboards applications where multi-metering is required. These applications include shopping centers, office buildings, and other commercial buildings with multiple tenants. Type SMM switchboards are designed to meet west-coast utility specifications. Type MMS switchboards are similar to the SMM switchboards, but utilize a ringless type meter, manual bypass, and no test blocks. The switchboard main service is rated up to 4000 amps at 480 volts, and service mains are rated up to 2000 amps for both types of switchboards. Commercial metering switchboards can be supplied with 2, 3, 4, or 6 sockets.

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Panelboard Example

When choosing between a panelboard and a switchboard in commercial applications, it is not always clear which product you should chose. There are a number of factors to consider such as total load, routing of the electrical power throughout a building, and future expansion. For example, in a small commercial application 480 volts supplied by the utility is applied to the input of a panelboard. Various outputs are used to supply power throughout the facility. One output might be used to supply power to a second panelboard through a transformer which is used for lighting and electrical outlets. Another output might be used to supply power to a motor through a motor starter.

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Switchboard Example

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In larger or more demanding commercial applications, switchboards can also be used to distribute power. For example, 480 volts supplied by the utility is applied to the input of a switchboard. One output might be used to supply power to a small panelboard through a transformer which is used for lighting and electrical outlets. Another output might be used to supply power to a larger panelboard located further away or on another floor. This panelboard supplies power to another panelboard for lighting and receptacles in that area. In addition, the panelboard supplies power to control a motor.

Circuit Breakers

Circuit breakers are used in panelboards and switchboards to provide circuit protection and provide a means of energizing and de-energizing a circuit. Siemens Sentron molded case circuit breakers (MCCB) used in panelboards are available with current ratings from 15 to 1200 amps.

Sentron series molded case circuit breakers used in switchboards are available up to 2000 amps. Siemens encased systems breakers are generically called insulated case circuit breakers (ICCB). Siemens insulated case circuit breakers are available with current ratings up to 5000 amps.

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Fusible Disconnect Switch

A fusible disconnect switch is another type of device used in panelboards and switchboards to provide overcurrent protection. Properly sized fuses located in the switch open when an overcurrent condition exists. Siemens fusible switches are available with ampere ratings from 30 to 1200 amps.

Bolted Pressure Switches

Bolted pressure switches are also used in switchboards as main disconnects. Bolted pressure switches are available in ratings up to 4000 amps.

Type RL Circuit Breaker

Siemens RL series low voltage power circuit breakers can also be used in Siemens switchboards. RL series circuit breakers are designed with current carrying capacities up to 5000 amps.

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Meters

Siemens offers a full line of power meters for use in the service section of switchboards. Meters can be used to measure real-time RMS (root-mean-square) values of phase currents, phase and line voltages, power usage, power factor, and peak demand. In addition, Siemens also has meters capable of monitoring power quality, such as K-factor, crest factor, individual harmonics, and total harmonics. Meters such as the 9350 and 9600 can act as a Web server. When combined with an Ethernet port, these meters offer quick and easy access to monitored values without the need for special software.

ACCESS™

Siemens meters have communication capability using the Siemens ACCESS system software. Siemens ACCESS is more than just power meters and other hardware. The ACCESS power management and control system is a networked system comprised of a variety of devices that monitor and control an electrical distribution system. The ACCESS system provides electrical data necessary for troubleshooting, power quality studies, preventative maintenance, and cost allocation. A power monitoring and management system, such as Siemens ACCESS, can identify potential problems before they cause costly breakdowns. Here are just five benefits to using the ACCESS system. • • • • •

Reduce or eliminate unplanned outages Proactively manage power systems to minimize utility bills Automate allocation of utility power bills Optimize existing capital equipment used in power systems Record and analyze power quality and power system anomalies

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TPS

Computers and other office equipment are susceptible to the high energy levels caused by an electrical surge, whether it is caused by electrical equipment or lightning. Any component between the source of the surge and ground can be damaged. One option available to protect equipment from electrical surges is the Siemens TPS (transient protection system). The TPS clamps voltage spikes before they damage expensive and sensitive equipment. Siemens TPS can be used with busway, panelboards, and switchboards.

AC Motors

AC motors, such as the Siemens Medallion™ motors, can be found in a variety of applications in commercial buildings. Siemens Medallion EPACT efficiency motors are high performance motors designed to meet the requirements of the U.S. Energy Policy Act of 1992 (EPAct). EPACT efficiency motors are available from 1 to 200 HP. Siemens Medallion PE-21 Plus motors are premium efficiency motors available from 1 to 500 HP. Premium efficiency motors typically cost slightly more than standard efficiency motors, but payback is in energy savings.

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Motors can be found on fans, pumps, elevators, escalators, and conveyors. A small conveyor, for example, might be used in a department store to move packages from a storeroom to a customer pickup location.

Safety Switches

Safety switches provide a means for a service entrance or a disconnecting means and fault protection for motors. A safety switch is simply a switch located in its own enclosure. The enclosure provides a degree of protection to personnel against incidental contact with live electrical equipment. Safety switches are available with or without provisions for fuses. Siemens enclosed switches are available with current ratings from 30 amps to 4000 amps.

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Motor Starter

Although safety switches can be used to start and stop motors, many motor applications require the use of remote control devices to start and stop the motor. Motor starters are commonly used to provide this function. Some motor starters have multi-speed and reversing capability.

A motor starter consists of a magnetic contactor and an overload relay. The contactor is an electromagnetic device used to close and open a set of contacts, which starts and stops the connected motor. If an overload occurs, excessive heat can build up in a motor which can damage the motor’s winding insulation. The overload relay will automatically stop the motor in this event.

Siemens manufactures a variety of starters, such as the Furnas INNOVA PLUS and the Furnas ESP100.

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Review 2 1.

____________ may be accessible from the rear as well as the front? a. c. Above

Load Centers Switchboards

b. d.

Panelboards All the

2.

____________ is a system manufactured by Siemens to provide protection in panelboards, switchboards, and busway from electrical surges.

3.

Switchboards typically consist of a service section and one or more ____________ sections.

4.

The ____________ commercial metering switchboards are designed to meet west coast utility specifications.

5.

Siemens safety switches are available with current ratings from 30 to ____________ amps.

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Industrial Applications

Voltage Classes

Electrical power requirement is a major consideration in industrial applications. Typically voltage is received and distributed at much higher levels than residential and commercial applications. Equipment must be specially designed to receive high transmission voltage from a utility company, and effectively distribute it throughout the industrial facility. Industrial facilities typically make large demands on the electrical utility, making it impractical to supply voltage at lower levels. The level of voltage supplied by the utility company varies with the requirements of the facility. For discussion purposes, it is sometimes convenient to divide voltages into classes. The Institute of Electrical and Electronics Engineers (IEEE), for example, divides voltage systems into the following classes:

Since the voltages supplied to the industrial facilities are typically either low or medium voltages, this discussion will focus on low and medium voltage systems beginning with a discussion of switchgear.

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Switchgear

The term switchgear is used to describe coordinated devices used for control and protection of equipment such as generators, transformers, capacitor banks, motors, and distribution lines. Switchgear is accessible from the front and rear. Siemens manufactures switchgear for low- and mediumvoltage applications.

Medium-Voltage Switchgear

Medium-voltage switchgear normally conforms to design requirements for metal-clad switchgear. Siemens manufactures medium-voltage switchgear rated at various levels to meet the requirements of typical medium-voltage applications found in many industrial facilities.

38 kV Switchgear

Siemens 38 kV medium-voltage, metal-clad switchgear is rated for voltages between 16.5 kV (16,000 volts) and 38 kV (38,000 volts). Siemens metal-clad switchgear features 38-3AF circuit breakers which are available in 1200, 2000, and 3000 amp current ratings.

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5 - 15 kV Switchgear

Siemens 5 - 15 kV metal-clad switchgear is designed to handle voltages of 4.16 kV (4160 volts), 7.2 kV (7200 volts), and 13.8 kV (13,800 volts). Siemens 5 - 15 kV switchgear features vacuum circuit breakers rated for 1200, 2000, and 3000 amps.

NXAIR P

NXAIR P medium voltage switchgear is “arc vented” . This design handles arc fault events more safely by directing expanding gases of an arc fault up and away from the operator. NXAIR P meets American standards (ANSI) and international standards (IEC) for global compliance. NXAIR P handles voltages from 5 kV to 15 kV with vacuum type circuit breakers rated from 1200 amps to 4000 amps.

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Medium-Voltage Switchgear Example

A large industrial facility, such as a paper or steel mill, receives electrical power at a substation from the utility company at high transmission voltage levels. The voltage is stepped down to a medium-voltage level at the substation for distribution by the industrial facility. Large industrial facilities can be spread out over several acres and incorporate many large buildings. Exact power distribution will depend on machinery location and power requirements. Multiple medium-voltage, metal-clad switchgear units could be used if the facility and the power demand were large enough.

It can be seen in this example that one 38 kV metal-clad switchgear unit is supplying power to two 5 kV metal-clad switchgear units and one 15 kV metal-clad switchgear unit. This is one way power might be distributed throughout a large industrial complex made up of several buildings, each requiring great amounts of electrical power.

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Low-Voltage Switchgear

Low-voltage switchgear normally conforms to the design requirements for metal-enclosed switchgear. Siemens lowvoltage switchgear can be used on distribution systems with 208, 240, 480, or 600 volts with currents up to 5000 amps in the Type R (indoor) and 4000 amps in the Type SR (outdoor). TPS (transient protection system) is available for Type R, low voltage switchgear applications.


Siemens RL series low voltage power circuit breakers are used in the Siemens low voltage switchgear. RL series circuit breakers are designed for up to 600-volt service with current carrying capacities up to 5000 amps.

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Secondary Unit Substation

Another method used to handle distribution voltage is with a secondary unit substation. A typical secondary unit substation consists of three sections which are coordinated in design to form one uniform enclosure. 1.

An incoming section that accepts incoming voltage and may include a primary switch.

2.

A transformer section that transforms incoming voltage down to a utilization voltage.

3.

An outgoing section that distributes power to outgoing feeders and provides protection for these feeders.

A primary switch is used to provide a means to connect and disconnect the secondary unit substation from the supply service. The transformer section can be liquid filled, ventilated dry type, or a cast-coil type. The outgoing section can be a Siemens Sentron switchboard, such as the RCIII, or Type R lowvoltage switchgear.

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Small Industrial Facility

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A small industrial facility might use a distribution scheme similar to the one shown below. In this example, transmission voltage is stepped down to 15 kV and applied to the input of the facility’s secondary unit substation. The transformer located in the substation steps the voltage down to 480 volts where it is distributed to various switchboards and panelboards.

Large Industrial Facility

A large industrial facility might use a power distribution scheme similar to the one shown below. In this application power is received at the industrial facility’s substation where it is stepped down to 38 kV for distribution. The distribution voltage is applied to the input of a 38 kV medium-voltage, metal-clad switchgear unit. One distribution branch is stepped down to 15 kV and applied to the input of a 15 kV switchgear unit. One of the outputs of the 15 kV switchgear is applied to the input of a secondary unit substation which uses low-voltage switchgear to distribute 480 volts throughout one section of the facility. The other outputs of the various switchgear units can be used to similarly distribute power.

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Busway

Even in large industrial facilities supply voltage must be reduced to a level that can be used by most electrical equipment. AC motors, drives, and motor control centers, for example, typically operate on 480 volts. General lighting and electrical receptacles operate on 120 volts. Busway is widely used in industrial applications to distribute this electrical power.

Types of Busway

Feeder busway is used to distribute power to loads that are concentrated in one physical area. Industrial applications frequently involve long runs from the power source to a single load. This load may be a large machine, motor control center, panelboard, or switchboard. Feeder busway sections are available in 0.125” increments from 2’ to 10’. Plug-in busway is used in applications where power requirements are distributed over a large area. Using plug-in units, load connections can be added or relocated easily. Sentron™ plug-in busway is available in 4’, 6’, 8’, and 10’ lengths.

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Busway runs also include a number of components such as tees, offsets, and elbows used to route busway through the facility.

Busway Example

In this example, busway is used to transfer power from switchgear located outside a building to a switchboard located inside a building. Electrical power is then distributed to various locations in the industrial facility. Siemens Sentron busway is available with current ratings up to 5000 amps at 600 volts.

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Review 3

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1.

Voltages less than 1000 volts are classed as ____________ voltage.

2.

Siemens 38 kV medium voltage, metal-clad switchgear is rated between ____________ kV and 38 kV.

3.

Siemens type ____________ low voltage switchgear can be used outdoors.

4.

The ____________ section of a secondary unit substation transforms incoming voltage down to a utilization voltage.

5.

____________ busway is used to distribute power to a single load that is located a long way from the power source.

Manufacturing Applications

So far, discussion in this course has primarily centered on power distribution. We have seen how Siemens products can be used to distribute power throughout residential, commercial, and industrial applications. In industrial applications, this electrical energy is also used for lighting, heating, air conditioning, office equipment, and other non-industrial systems. Unlike commercial and residential applications, however, most of the electrical energy is used to power manufacturing equipment.

The equipment used in manufacturing varies widely depending upon the volume of production and the types of processes employed. As a result, Siemens offers a vast array of products for use in virtually every phase of manufacturing. Many of these products are purchased by machine builders or OEMs (original equipment manufacturers) for resale to the end user. In other cases, the end user may engineer a machine or process line or employ another company to do the engineering. The end result, however, is a coordinated system or process.

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There is a variety of ways to represent manufacturing processes. However, since the goal of this course is to present an overview of Siemens Energy & Automation products, we need only take a high-level view of manufacturing processes. In general, we can say that most manufacturing processes consist of one or more of the following process types: Discrete Parts Manufacturing Assembly Batch Processing Continuous Processing The process type included in the overall manufacturing process depends upon the products being produced. Some industries, for example, are dominated by a specific process type. Process Type

Industry Examples

Discrete Parts Manufacturing

Aircraft Parts Automotive Parts Electrical & Electronic Parts

Assembly

Aircraft Motor Vehicle Computer

Batch Processing

Food & Beverage Pharmaceutical

Continuous Processing

Chemical Petroleum

As an aid to understanding Siemens Energy & Automation products, the next section of this course will provide examples of products that could be used in each of the process types previously listed. Given the diversity of products, only representative examples will be used.

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Discrete Parts Manufacturing

The process of manufacturing discrete parts typically involves the use of multiple machines. These machines may be involved with the movement and storage of raw materials, various stages of fabrication of raw materials into finished parts, packaging of parts, storage of parts, preparation of parts for shipment, and a host of related activities. PLC-Controlled Machine

Although the various machines used as part of this process may vary widely, a typical machine will need some type of control system. This control system may be a programmable logic controller (PLC), like the Siemens S7-200 shown in the following illustration. The PLC is an industrial computer that interconnects to the machine it is controlling largely through its input-output (I/O) system. The PLC’s I/O system allows it to receive inputs from switches and sensors and generate outputs to actuating devices, such as contactors and solenoids, and display devices such as indicator lights and Light Emitting Diode (LED) displays.

Light

Switch

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Input Devices

Inputs the PLC receives from various switches and sensors can provide signals representative of the actual condition of a machine. In addition, switches and other operator interfaces provide the PLC with signals representative of operator commands.

Inputs, as well as the current condition of PLC outputs and internal data values, are analyzed by the PLC’s stored program.

Output Devices

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The PLC uses this process to determine the signals it sends to output devices that control the operation of the machine or indicate machine conditions such as RUN or STOP.

Communication

In addition to signals provided to the PLC through its I/O system, the PLC may also communicate with other devices via one or more communication ports. Communication ports can provide a pathway for the PLC to communicate with devices such as operator interfaces, variable speed drives, computers, and other PLCs.

Human Machine Interface

A Human Machine Interface (HMI) is any device that acts as a link between the operator and the machine. Typically, however, the term HMI is used to refer to devices that display machine or process information and provide a means for entering data or commands. Siemens HMI products include both hardware, like the SIMATIC® HMI operator panels, and software, like WinCC®.

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Siemens PLCs

Since the characteristics of machines vary considerably, no one PLC can satisfy all machine control requirements. Therefore, Siemens provides PLCs of varying sizes and capabilities. The Siemens SIMATIC family of PLCs include the 505, S5, and the S7-200, S7-300, and S7-400, which are shown below.

SITOP Power Supplies

Depending on the application, PLCs, operator panels, and control components may require a regulated power supply. The SITOP® power supply provides a regulated source of 24 VDC power and the ability to ride through momentary power dips between 3 to 10 ms. Longer ride-through times can be achieved with an optional back up module which can provide up to 100 ms at 40 amps (200 ms at 20 amps and so on). An optional DC UPS (uninterruptable power supply) module and an external battery is also available. SITOP power supplies meet standards of agencies worldwide. They are suitable for use on worldwide networks and require no fusing on the secondary. Models are available up to 40 amps and SITOP can be used at 100% of the rated output current.

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Machine Example

In the machine example shown below, an S7-200 PLC is mounted in a machine’s control panel. The manufacturer of the machine has chosen to use field devices that require 24 VDC power. The power for the field devices and the PLC is provided by SITOP power supplies, one of which is shown adjacent to the S7-200. As the S7-200 PLC executes its control program, it receives inputs from manual switches mounted on the front of the panel. It also communicates with a SIMATIC HMI OP3 operator panel that provides for manual inputs from the machine operator or maintenance person and displays alphanumeric messages indicating machine status. The PLC also receives inputs from other control devices such as limit switches or proximity switches that change state as a result of machine operations. In this example, the outputs of the PLC control electromechanical devices such as motor starters and contactors that turn on and off to control various aspects of the machine. OP3

S7-200

SITOP

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CNC-Controlled Machine Tool

PLCs are not the only control systems used for machines. Machine tools such as lathes, grinding machines, and machining centers are used to produce precisely machined parts. Machine tools typically combine a PLC control system with a computer numerical control (CNC). CNC-controlled machine tools allow parts to be machined to complex and exacting specifications. A gear, similar to the one illustrated, is one example of a part that might be made with a CNC-controlled machine tool.

SINUMERIK

Siemens offers a range of SINUMERIK® CNC models such as the 810D, 840Di, 840D, and the compact FM357-2 positioning and path control module. These products provide the coordinated multi-axis control needed for milling, drilling, turning, and grinding applications. SINUMERIK CNCs also interconnect operator panels and SIMODRIVE servo and spindle drives and associated motors to form a complete control system for the machine tool.

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Machine Tool Example

Typically, machine tools are designed to perform a specific task, such as grinding, drilling, or cutting. Machine tools can be programmed to a predetermined pattern or model to obtain the desired shape of the finished piece. In the following example a SINUMERIK CNC controls a rotary grinding machine. The rotary grinding machine takes a piece of stock that has already been cut and shaped on another machine tool, removes any burrs or high spots, and grinds the material to a fine finish.

Review 4 1.

A ____________ is an example of an output device used for a PLC. a. b. c. d.

2.

pushbutton pilot light photoelectric sensor limit switch

The term “SIMATIC HMI” is used to identify a type of ____________ manufactured by Siemens. a. b. c. d.

PLC power supply operator panel machine tool

3.

SITOP power supplies provide a regulated source of ____________ VDC.

4.

____________ is a Siemens trade name that identifies a complete control system used in the machine tool industry.

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Assembly Processes

Assembly processes may involve assembling an entire system or subsystem at one location. In many cases, however, parts may be mounted sequentially through a series of assembly stations. Units being assembled are then moved from station to station via some type of transporter mechanism such as a conveyor. Any specific assembly station may utilize only manual assembly operations or may include one or more machine operations. The latter is particularly true when just-in-time manufacturing techniques requiring parts to be manufactured as needed are employed.

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Motors

There are many aspects of assembly processes that are similar to discrete parts manufacturing and, in fact, many factories combine both types of processes. Therefore, it should come as no surprise that the electrical products used in both types of processes are often the same. For instance, AC motors are used in both types of processes to change electrical energy into mechanical energy, the reverse of what a generator does. In the U.S. the most common type of industrial motor is a NEMA frame size, three-phase AC induction motor. The term “NEMA frame size” is used to indicate that the motor corresponds to frame dimensions specified by the National Electrical Manufacturers Association. Siemens manufactures a variety of motors, including motors too large to correspond to NEMA frame dimensions (above NEMA motors) and motors that correspond to International Electrotechnical Commission (IEC) specifications.

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Motor Control

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Wherever motors are used, they must be controlled. The most basic type of AC motor control involves turning the motor on and off. This is often accomplished by using a motor starter, which is made up of a contactor and an overload relay. The contactor’s contacts are closed to start the motor and opened to stop the motor. This is accomplished electromechanically using start and stop pushbuttons or other pilot devices wired to control the contactor. The overload relay protects the motor by disconnecting power to the motor when an overload condition exists. An overload could occur, for instance, when a conveyor is jammed. Although the overload relay provides protection from overloads, it does not provide short-circuit protection for the wiring providing power to the motor. For this reason, a circuit breaker or fuses are also used.

Motor Control Centers

When only a few geographically dispersed AC motors are used, the circuit protection and control components may be located in a panel near the motor. When a larger number of motors are used these components are often concentrated in a motor control center. A motor control center is a type of enclosure that is sectionalized so that control circuits associated with each motor are mounted in a removable container called a pan or bucket. Siemens TIASTAR motor control centers can be manufactured to fit a wide range of customer requirements. Motor control centers can also include items such as reducedvoltage controllers, variable speed drives, and PLCs.

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Reduced Voltage Controllers While it is common to turn motors on and off instantaneously, this abrupt transition results in power surges and mechanical shock that may need to be avoided especially when larger motors are involved. Solid-state reduced-voltage controllers, however, can apply voltage gradually from an initial low voltage to 100% voltage. The motor experiences reduced inrush current and speed is accelerated smoothly. In addition, just enough torque can be applied to start and accelerate the motor. This is beneficial for loads that have problems with the initial jerk and rapid acceleration of across-the-line starting. Reduced-voltage controllers, such as the Siemens SIRIUS and SIKOSTART, can also be included in Siemens motor control centers.

AC Drives

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Although reduced voltage controllers can control an AC motor during starting and stopping, many applications require control of motor speed and torque. Controlling motor speed and torque is the job of a variable speed drive. Since AC motors are available in a range of ratings and types, Siemens offers a broad range of AC drives, including multiple models of the MICROMASTER and MASTERDRIVE.

DC Drives

Although AC motors are more commonly used, many factories also use DC motors for selected applications. In many of these applications, precise control of motor speed and torque is required. For these applications Siemens offers the SIMOREG® DC MASTER.

PLCs

Since assembly processes vary in complexity, the types of control systems and related devices employed will also vary. In addition to small- and medium-sized PLCs or other control systems used to control individual machines, one or more larger PLCs may be employed to collect data and coordinate operation of some or all of the system. This overall coordination may include control of the full range of motor control devices discussed thus far from full-voltage starters to AC and DC drives. The specific PLC model used will be determined by the size and complexity of the application. Examples of Siemens PLC models that may be employed include the S7-300 and S7-400.

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Human Machine Interface

Just as it is often necessary to use a PLC to coordinate the operation of multiple machines in an assembly process, it is also often necessary to provide a graphical representation of the current status of this process. In addition to providing this graphical representation, a Human Machine Interface (HMI), such as Siemens WinCC, can provide a custom interface to allow operation personnel to control some or all of the process and for maintenance personnel to obtain system diagnostic information. Since many manufacturing facilities use multiple PLC models and often models produced by multiple companies, WinCC can communicate with many types of PLCs. In addition, WinCC versions are available for computers using Windows 95 or Windows NT operating systems.

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Local Area Network

In any complex assembly process the need for rapid information flow is critical. Conditions at any point in the process may impact the entire process. This need for information flow often requires that intelligent devices such as PLCs, intelligent sensors, drives, computers, and operator interface systems be interconnected by one or more local area networks (LAN). A LAN is a communication system designed for private use in a limited area. LANs are used in office areas as well as in manufacturing environments; however, LANs used in industrial applications must be able to operate reliably in conditions that might be unsuitable for office-grade equipment. Industrial environments typically have a high level of electrical noise and a greater range of temperature and humidity than found in office environments. Specifications for industrial LANs vary considerably depending upon the requirements of the application. Issues such as the amount of data to be communicated, the rate at which data must be communicated, the number of devices to be connected, the reliability and noise immunity required, compatibility with other networks, and cost are examples of important considerations. In general, it is not possible for one network type to maximize all characteristics. For instance, a network that can communicate a large amount of data in a short time is likely to be more expensive than a network that has more limited requirements. Therefore, many factories use a multi-level structure for communication. In the past, these networks were often proprietary systems designed to a specific vendor’s standards. Siemens has been a leader in pushing the trend to open systems based upon international standards developed through industry associations. Examples of these open networks are listed below.

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Batch and Continuous Processes

Thus far, we have discussed equipment used in discrete parts manufacturing or assembly applications. In addition to these types of manufacturing processes, electrical equipment is also used to manufacture a variety of products using batch or continuous processes. Batch Processes

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Batch processes are familiar to most people since we use them in everyday life. For instance, when we bake a cake, we follow a recipe that involves adding ingredients, stirring the mixture, pouring it into baking pans, putting the pans into the oven for a specific time at a specific temperature, etc. Industrial batch processes are similar to the process of baking a cake but scaled up to produce a larger quantity of material. A variety of products are produced using batch processes. Food, beverages, pharmaceutical products, paint, fertilizer, and cement are a few of the categories of products produced using batch processes. Some products such as food, beverages, and pharmaceuticals require precise tracking of batch information for safety and regulatory purposes.

Continuous Processes

Continuous processes are less understood by most people; however, they have some similarities to batch processes. Ingredients must be combined in precise ways at precise points in the process. Precise control of process conditions must be maintained to ensure product quality and safety of operations. Some industries, such as chemical and petrochemical industries, use continuous processes extensively. Many other industries, however, use continuous processes as some part of their operations, purifying air and water, treating waste products, etc.

Both batch and continuous processes use many of the products discussed thus far. However, there are some unique characteristics of batch and continuous processes that either require the use of additional types of equipment or require some of the equipment previously discussed to be applied differently.

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Closed-Loop Control

One characteristic of batch and continuous processes is their extensive use of analog data. Analog values can vary continuously within a specified range. The analog data may be representative of temperature, pressure, rate of flow, weight, thickness, viscosity, humidity, or any other characteristic of importance to the process. Both batch and continuous processes require continuous monitoring at numerous points throughout the process. In addition, a corrective action is often required to insure that the process stays within specifications. This type of control that involves measuring a value, comparing the measured value to a desired value or set point, and correcting for the error is called closed-loop control.

A variety of approaches can be used for process control depending upon the complexity of the process being controlled. A small batch process often lends itself well to control by one PLC or a few networked PLCs. A representation of the process showing its current status and a history of data recorded at various points in the process is often provided to an HMI system networked to the PLCs.

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Increasingly, variable speed drives are also networked to the PLC and HMI systems. These drives are used to control the speed of pumps or fans that in turn control the flow of fluids and gases. Flow control is frequently accomplished by using control valves and vent damping systems to regulate flow while running pump and fan motors at full voltage. Using variable speed drives for pump and fan control is a more energy efficient approach to controlling process flow rates.

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Supervisory Control

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Traditionally, medium to large applications in process industries have been controlled by distributed control systems (DCS) that are based on proprietary hardware and software. By utilizing industrial standards (Microsoft NT, Ethernet, PROFIBUS) the industry now moves towards scalable hybrid systems, like SIMATIC PCS 7. Hybrid systems contain powerful process controllers and networks combined with all software tools integrated into one common Engineering system. By using PCS 7, customers reduce engineering time, installation costs and spare part inventory. PCS 7 is built upon Totally Integrated Automation components and provides a complete toolset for developing the control strategy, the HMI, networks and interfaces to MES/ERP systems.

Other STEP 2000 Courses

Hopefully, this course along with our STEP 2000 Basics of Electricity course, has provided you with a base of knowledge that will make our other STEP 2000 courses more useful and interesting to you. Keep this book handy so that you can use the pictorial glossary to assist you in your additional training or with your daily work.

Review 5 1.

____________ ____________ controllers start a motor by applying voltage gradually from an initial low voltage to 100% voltage.

2.

An AC or DC ____________ is used to control the speed and torque of a motor.

3.

____________ is a name associated with three types of LANs that are used at the field and process level.

4.

____________ is an example of a LAN that is used at the device level.

5.

Paint, fertilizer, and cement are examples of ____________ processes.

6.

____________ - ____________ involves measuring a value, comparing the measured value to a desired set point, and correcting the error.

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Pictorial Glossary

The pictorial glossary includes definitions and illustrations to many terms that are frequently used in the electrical industry. Terms that are underlined and italicized are included in the glossary as a separate definition. AC Drive

An electronic device used to control the speed and torque of an AC motor. Also called a variable frequency drive, variable speed drive, and an inverter.

AC Motor

A motor that uses alternating current to convert electrical energy into mechanical energy. Many AC motors used in industrial applications are three-phase induction motors.

Alternating Current (AC)

Current that periodically reverses direction. + Direction

0

_

Ambient Temperature 70

Time

Direction

The temperature of the medium (air, water, etc.) surrounding a device.

American National Standards Institute (ANSI)

A nongovernmental organization that promotes and coordinates the development of standards and approves standards written by other organizations.

American Standard Code for Information Interchange (ASCII)

A seven-bit code, sometimes with an additional parity bit added for error checking. The ASCII code is used to represent numbers, letters, symbols, and control codes.

American Wire Gage (AWG)

A common method of specifying wire size (cross-sectional area). Larger numbers represent smaller wires. After AWG No. 1, the largest sizes are AWG No. 0, AWG No. 00, AWG No. 000, and AWG 0000. AWG No. 0 is called one-aught, AWG No. 00 is called two-aught, etc.

Ammeter

A meter designed to measure current.

Ampacity

The rated continuous current capacity of a conductor or device.

Ampere, Amp

The basic unit for current. The ampere, also called an amp, is equal to a current of 1 Columb per second. The symbol for ampere is “A.”

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Amplitude

The total variation of a waveform. Amplitude can be expressed as a peak value, peak-to-peak value, or effective value. + Peak Value

+

0

0 Time

_

Time

Peak-To-Peak Value

_

Peak Value

Analog

A value that is continuously variable. Also used to describe circuits that work with analog signals.

Analog Input

An input to a system that can continuously vary over a range of current or voltage such as 4 to 20 milliamps or 0 to 10 volts.

Analog Output

An output from a system that can continuously vary over a range of current or voltage such as 4 to 20 milliamps or 0 to 10 volts. Transducer PLC Analog Output 0 - 10 VDC

Analog-to-Digital (A/D) Converter

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Analog Weight Meter

Voltage - Weight

Weight 0 - 500 Lbs

A circuit that converts analog signals to signals that can be used by digital circuits.

Apparent Power

The vector sum of true power and reactive power. Apparent power is calculated by multiplying current times voltage. The unit for apparent power is the volt-ampere or VA.

Arc Chute Assembly

An assembly of metal plates surrounding circuit breaker or contactor contacts. The arc chutes are used to reduce contact damage by quickly extinguishing the arc created when circuit breaker contacts open.

Arc Fault

An arc fault occurs when a current-carrying conductor has arcing condition to ground or another conductor.

Arc Fault Circuit Interrupter (AFCI)

A circuit breaker designed to provide protection from the effects of an arc fault by recognizing the characteristics unique to arcing and de-energizing the circuit when an arc fault is detected.

Autotransformer

A type of transformer in which the secondary coil is part of the primary coil. Often the secondary voltage is adjustable via a movable tap.

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Baud Rate

A way of describing the amount of data that can be sent on a signal line. Often used synonymously with bits per second; however, baud rate was originally intended for use in telegraphy application to refer to signal events per second.

Binary-Coded Decimal (BCD)

Usually refers to the 8-4-2-1 code where four bits are used to represent decimal digits 0 through 9.

0

2

Decimal Numbers 0 1 2 3 4 5 6 7 8 9

5

0

0000 0010 0000 0101

Binary Number

A number made up only of 1’s and 0’s that represent powers of two (2). Digital equipment uses binary numbers to represent numerical values or the on or off condition of devices. Most Significant Bit 7

Bit

BCD Numbers 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001

6

Least Significant Bit

5

4

3

2 128

2 64

2 32

2 16

2 8

22 4

21 2

20 1

0

0

0

1

1

0

0

0

A 1 or 0 representing one position in a binary number. Bit 0

0

0

1

1

0

0

0

0

0

0

1

1

0

0

0

Byte Word

Bonding

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The permanent joining of metal parts to form an electrically conductive path.

Branch Circuit

A part of a power distribution system extending beyond the final overcurrent protection device.

Bus

A group of conductors used to supply power, data, or control signals downstream. Buses

Bus Bar

A conductor that serves as a common connection for two or more circuits.

Bus Plug

A device used with plug-in busway to allow power to be distributed to a load.

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Busway

A prefabricated electrical distribution system that uses bus bars in its own protective enclosure.

Busway Hangers

Devices used to suspend busway from a ceiling or mount it to a wall.

Byte

Eight consecutive bits.

Capacitance

The property of a circuit that allows it to store an electrical charge. The symbol for capacitance is “C.” The unit for capacitance is the farad.

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Capacitive Proximity Sensor A type of sensing switch that produces an electrostatic field to detect the presence of metal and nonmetallic objects without coming into contact with them.

Capacitive Reactance

The opposition to alternating current resulting from circuit capacitance. Capacitive reactance is inversely proportional to frequency and capacitance. The symbol for capacitive reactance is “XC.” The unit for capacitive reactance is the ohm.

Capacitor

A device manufactured to have a specific capacitance.

Central Processor Unit (CPU) The decision-making part of a computer. May also be used to describe the processing circuits together with memory and other circuits needed for processing information.

Circuit Breaker

A device that can be used to open or close a circuit manually and can also open a circuit automatically when current is excessive.

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Closed-Loop Control

A control technique that compares a feedback signal representative of an actual value with a desired value and responds to minimize the error.

Conductor

A material that permits many electrons to move through it. Copper, silver, and aluminum are examples of materials that are good conductors. Also used generically to refer to a wire, cable, or bus bar that is made from a conducting material. Rubber Insulator Copper Conductor

Contactor

A device used to energize and de-energize an electrical circuit.

Control Relay

A device used to remotely open and close contacts.

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Single-Pole Single-Throw Single-Break

Double-Pole Single-Throw Single-Break

Single-Pole Single-Throw Double-Break

Double-Pole Single-Throw Double-Break

Single-Pole Double-Throw Single-Break

Double-Pole Double-Throw Single-Break

Single-Pole Double-Throw Double-Break

Double-Pole Double-Throw Double-Break

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Coulomb

A unit of electrical charge equal to 6.24 x 10 electrons.

Coulomb’s Law

A law that states that charged objects attract or repel each other with a force that is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. Unlike charges attract, and like charges repel each other. Unlike Charges Attract

Like Charges Repel

Counter emf

A voltage created in an inductive circuit that opposes a change in current flow.

Crest Factor

A ratio of the peak value of an alternating current source to the effective value.

Current

The flow of electrons in a circuit. Current is designated by the symbol “I” and is measured in amperes.

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DC Drive

An electronic device used to control the speed and torque of a DC motor. Also called a variable speed drive or an adjustable speed drive.

DC Motor

A motor that converts direct current electrical energy into mechanical energy.

Dead Front

A front portion of a panelboard or switchboard that limits exposure to electrical connections.

Delta

A connection arrangement used for the primary and/or secondary of a three-phase transformer.

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Digital

Used to describe circuits that use on or off (binary) signals. Also used to describe equipment that includes these circuits.

Digital-to-Analog (D/A) Converter

A circuit that converts digital signals to signals that can be used by analog devices.

DIN

DIN is the German Institute for standardization. DIN has been recognized since 1975 as the standards organization that represents German interests nationally and internationally.

DIN Rail

A mounting bracket manufactured to DIN specifications. Typically used to mount devices such as small PLCs, motor starters, relays, and other components that are DIN rail compatable.

Diode

A component with two terminals (anode and cathode) that passes current primarily in one direction. Often used as part of a rectifier circuit.

Direct Current (DC)

Current with a constant direction.

Disconnect Switch

A switch designed to disconnect electrical power from a circuit.

Discrete Input

An input that is either on or off.

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Discrete Output

An output that is either on or off.

Distribution Section

A section of switchboard that receives power from the service section.

Duty Cycle

The ratio of a device’s on time to its total cycle time. Duty cycle is normally expressed as a percentage; therefore, a device with a 50% duty cycle is on half the time.

Effective Value

A measure of the amplitude of alternating current or voltage. Also called the root-mean-square or RMS value. Test meters used to measure alternating current or voltage usually display effective values. + Peak value 169.7 volts 0

_ 169.7 Vpeak x .707 = 120 Vrms

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Electrically Erasable Programmable Read Only Memory (EEPROM)

A type of semiconductor memory often used for storage of data or programs that change infrequently. The contents of EEPROM chips are erased with electrical pulses rather than with ultraviolet light as with erasable programmable read only memory. EEPROMs retain their contents when power is lost. RAM

EEPROM

Executed Program

Program backup

Current Data

Parameters

Memory bits, timers, counters

Enclosure

A case or housing. Guidelines for various types of electrical enclosures are provided by the National Electrical Manufacturers Association (NEMA).

Encoder

Often refers to a digital device that provides angular position information. Some encoders provide this information as incremental pulses as position changes. Other types of encoders provide a digital signal representative of absolute position.

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Erasable Programmable Read Only Memory

A type of semiconductor memory often used for storage of data or programs that change infrequently. EPROM chips must be removed from the circuit to be erased and reprogrammed. EEPROMS retain their contents when power is lost.

Explosion Proof (XP)

A motor enclosure type used in hazardous locations. Explosion proof enclosures are also available for other types of equipment.

Farad

The basic unit of capacitance. The symbol for the farad is “F.”

Feedback

A signal provided to a control circuit that is representative of an actual condition in a machine or process.

Feeder

A set of conductors that originates at a main distribution center and supplies power to one or more secondary or branch distribution centers. Utility Supply 120/208 Volts 3-Phase, 4-Wire

Feeders

Branches

208 Volt Electric Heating Unit

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208 Volt Parking Lot Lighting

120 Volt Lighting And Receptacles

208 Volt Air Conditioning Unit

Feeder Busway

Busway used to distribute power, often over a long run, to loads concentrated in one area.

Filler Plates

Plates used to cover unused spaces in a panel.

Four-Quadrant Operation

Describes the operation of a variable speed drive that is capable of providing forward or reverse torque with the motor rotating in either the forward or reverse direction.

T = Torque N = Speed

Frequency

The rate of variation of a periodic waveform. The symbol for frequency is “f.” The unit for frequency is Hz.

Full-Voltage Starter

A type of motor starter often used for three-phase induction motors that applies the full-line voltage to the motor immediately. Sometimes called an across-the-line starter.

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Fuse

A device designed to open a circuit when its rated current is exceeded. This is usually accomplished when a metal link in the fuse melts. Fuses are available in various sizes and types. Some have a time delay or more than one element.

Fuse Class

A letter designation given to a fuse to identify its operating and construction characteristics. Class H K R J L

AIC Rating 10,000 A 50,000 A 200,000 A 200,000 A 200,000 A

Ground

A connection to the earth or to a conductive object such as an equipment chassis.

Ground Fault

A condition in which current unintentionally flows to ground.

Ground Fault Circuit Interrupter (GFCI)

A device designed to interrupt current in a circuit if the current in the hot wire is not equal to current in the neutral wire. Trip Coil

Sensing and Test Circuit

Hot Wire 120 volts Neutral Ground Fault Circuit Interrupter

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Harmonics

The base frequency of a power supply is said to be the fundamental frequency or first harmonic. Additional harmonics can appear on the power supply which are usually whole number multiples of the first harmonic. The 3rd harmonic of a 60 Hz power supply, for example, is 180 Hz (3 x 60).

Harmonic Distortion

The effect of harmonics on the fundamental frequency. Harmonic distortion is destructive and inteferes with the operation of electronic devices.

Henry

The basic unit of inductance. The symbol for the henry is “H.”

Hertz

A unit of frequency equal to one cycle per second. Hertz is abbreviated Hz.

Hexadecimal

A number system that uses powers of 16.

Horsepower

A unit of power. Horsepower is symbolized by “HP.” 1 horsepower is equal to 746 watts.

Impedance

The total opposition to alternating current. Impedance is the vector sum of resistance and reactance. The symbol for impedance is “Z.” The unit for impedance is the ohm.

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Inductance

The property of an electrical circuit that causes it to oppose changes in current. Inductance is designated by the symbol “L” and is measured in henries.

Inductive Proximity Sensor

A type of sensing switch that uses an electromagnetic coil to detect the presence of a metal object without coming into physical contact with it. Inductive proximity sensors ignore nonmetallic objects.

Inductive Reactance

The opposition to alternating current resulting from circuit inductance. Inductive reactance is directly proportional to frequency and inductance. The symbol for inductive reactance is “XL.” The unit for inductive reactance is the ohm. XL = 2πfl

Inductor

A device manufactured to have a specific inductance. An inductor is made from a coil of wire and is sometimes called a coil or choke.

N

Input/Output (I/O) System

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S

The part of a control system that interfaces to the real world. The I/O system accepts signals from switches and sensors, and provides signals to actuating devices, indicators, etc.

Institute of Electrical and Electronic Engineers (IEEE)

An organization open to individual membership that provides a variety of services for its members, but also develops numerous standards for electrical and electronic equipment and practices.

Instrument Transformer

A type of transformer used to allow circuits to sense the voltage or current of associated conductors. A potential transformer (PT) is used to step-down voltage. A current transformer (CT) is used to sense the level of current.

Insulated Case Circuit Breaker (ICCB)

A type of circuit breaker that combines the high interrupting rating of a molded case circuit breaker with the high shorttime ratings of a power circuit breaker. Also called an encased systems breaker.

Insulated Gate Bipolar Transistor (IGBT)

A type of transistor often used as a switching device in the inverter section of a variable frequency drive. Voltage on the gate element is used to control the current flowing between the collector and emitter. Collector

VCE Gate (+) Emitter

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Insulation Class

Standards established by the National Electrical Manufacturers Association (NEMA) to meet motor temperature requirements found in different operating environments. The combination of an ambient temperature of 40°C and allowed temperature rise equals the maximum winding temperature of a motor. A margin is also allowed to provide for a point at the center of the motor’s windings where the temperature is higher.

Insulator

A material with a high resistance to the flow of electrons. Plastic, rubber, glass, and mica are examples of materials that are good insulators.

International Electrotechnical Commission (IEC)

An organization based in Geneva, Switzerland, with over 50 member nations. IEC writes standards for electrical and electronic equipment and practices.

Interrupting Rating

The maximum level of fault current that a circuit breaker or fuse can interrupt. The interrupting rating is also called the ampere interrupting capacity (AIC).

Inverter

A device that converts direct current to alternating current. Inverter is also used as a synonym for an AC drive even though the AC drive usually includes other circuits. Inverter

650 VDC

ISO

90

Control Logic

IGBT

3Ø Motor

A federation of standards organizations from over 100 countries that develops voluntary standards for business, science, and technology. The official name is Organization Internationale de Normalisation. The name ISO is from the Greek word “isos” which means equal.

Isolation Transformer

A transformer used to limit the transfer of electrical noise from one circuit to another.

Joule

The basic unit of electrical energy. 1 Joule is equal to 1 wattsecond or the amount of energy transferred in one second when the power is one watt.

Knockout

A place in an enclosure where a piece of the enclosure can be removed to allow for cabling.

Ladder Logic

A method of programming a programmable logic controller that uses symbols that evolved from the diagrams used with control relays.

Limit Switch

A type of sensing switch that opens or closes its contacts when its actuator is moved by an object.

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Limit Switch Positions

The following terms identify the operating positions of a limit switch.

Load-Break Switch

A switch designed to safely interrupt load current.

Load Center

An industry term used to identify a lighting and appliance panelboard when it is used in certain (usually residential) applications.

Local Area Network (LAN)

A communication system that interconnects intelligent devices within a limited area, but may also connect other networks for larger-scale communication.

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Main Breaker

The circuit breaker in a load center, panelboard, switchboard, or switchgear that is connected to the source of supply.

Main Lug Only

A designation given to a load center or panelboard to indicate that it does not include a main breaker.

MCM

Thousands of circular mils. A method for designating the crosssectional area of a conductor; especially conductors larger than AWG 4/0 (four aught). One mill is equal to 1/1000 of an inch. Circular mil area is the diameter (in mils) of a circular conductor squared. 1 MCM is 1000 circular mils (also shown as 1kcmil).

Metric Unit Prefix

A prefix added to a unit of measure to increase or decrease the size of that unit of measure. For example, the metric unit prefix kilo can be added to meter to form a unit of length (kilometer) equal to 1000 meters. Metric unit prefixes are associated with powers of ten.

Microprocessor

The integrated circuit or chip that contains the central processor unit.

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Molded Case Circuit Breaker

A circuit breaker enclosed in an insulated housing. The housing is normally made of molded plastic.

Molded Case Switch

A switch enclosed in an insulated housing similar to that of a molded case circuit breaker.

Motor

A device used to transform electrical energy into mechanical energy.

Motor Control Center

A metal enclosure containing multiple motor control circuits. Typically, individual control circuits are mounted in removable containers often referred to as pans or buckets.

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Motor Insulation Class

A letter designation based upon standards established by the National Electrical Manufacturers Association that corresponds to a motor’s allowable temperature rise and maximum allowable operating temperature (based on 40°C ambient temperature). 180° 160° 140° 120° 100° 80° 60° 40° 20° 0°

5° 60°

180° 160° 140° 120° 100° 80° 60° 40° 20° 0°

Class A 60° C Rise 5° C Hot Spot

180° 160° 140° 120° 100° 80° 60° 40° 20° 0°

10° 80°

Class B 80° C Rise 10° C Hot Spot

10°

105°

180° 160° 140° 120° 100° 80° 60° 40° 20° 0°

Class F 105° C Rise 10° C Hot Spot

15°

125°

Class H 125° C Rise 15° C Hot Spot

Motor Starter

Often refers to a contactor and an overload relay assembled together to remotely control the operation of a motor while providing overload protection. This definition applies to a full voltage starter.

Mutual Induction

A process that involves varying lines of magnetic flux from one conductor that induce a voltage into a second adjacent conductor. This is the basic operating principle of a transformer. Ammeter

Ammeter

Ammeter

0

0

0

N

Time 1

S

Time 2

S

N

N

S

Time 3

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National Electrical Manufacturers Association (NEMA)

An organization of manufacturers of electrical equipment that, among other things, develops standards for electrical equipment.

National Electrical Code® (NEC ®)

A document revised every three years based upon inputs to and recommendations of the National Electrical Code Committee of the National Fire Protection Association. The intent of the NEC® is to describe safe electrical practices. Although the NEC® is an advisory document, its use is often incorporated into laws and regulatory practices.

National Fire Protection Association (NFPA)

A private, nonprofit organization with international membership. The NFPA has been the sponsor of the National Electrical Code® (NEC®) since 1911.

NEMA Enclosure Type

A designation given to an enclosure based on standards published by the National Electrical Manufacturers Association. The NEMA type provides an indication of degree of protection provided by the enclosure.

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NEMA Frame Size

A designation that identifies motor dimensions based upon standards provided by the National Electrical Manufacturers Association. Motors too large to correspond to NEMA frame sizes are referred to as above NEMA motors.

NEMA Motor Design

A letter designation based upon standards established by the National Electrical Manufacturers Association that corresponds to a motor’s speed and torque characteristics. 300 275

NEMA D

250 225

NEMA C

200 175

NEMA B

150 125 100

Full-Load Torque

75 50 25 0

0

10 20 30 40 50 60 70 80 90 100 % Synchronous Speed

Neutral

A reference connection in a power distribution system.

Primary

A 120 Volts Neutral

240 Volts

120 Volts B Ground

Ohm

The basic unit of resistance, reactance and impedance. The symbol for the ohm is “Ω”, the Greek letter omega.

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Ohmmeter

A meter designed to measure resistance.

Ohm’s Law

A law that states that the current in a circuit is directly proportional to the voltage and inversely proportional to the resistance.

Open Drip Proof (ODP)

A motor enclosure type that permits air flow through the motor, but is designed to prevent liquids or solids falling from above at angles up to 15 degrees from the vertical from entering the motor.

Open-Loop Control

A control technique that does not use a feedback signal.

Overcurrent

A current in excess of the rated current for a device or conductor. An overcurrent can result from an overload, short circuit, or ground fault.

Overload

Can refer to an operating condition in excess of a full-load rating or a current high enough to cause damage if it is present long enough. An overload does not refer to a short circuit or ground fault.

Overload Relay

A device used to protect a motor from damage resulting from an overcurrent.

Overload Relay Class

Defines the length of time an overcurrent condition can exist before an overload relay trips. For example, a class 10 overload relay will allow 600% of full load amperes for up to 10 seconds.

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Pad-Mounted Transformer

An enclosed transformer mounted outside on a concrete pad.

Panelboard

A front-accessible panel containing overcurrent protection devices for use in controlling lighting, heating, or power circuits.

Photoelectric Sensor

A type of sensing switch that uses light to detect the presence of an object without coming into physical contact with the object.

Pilot Light

A small light used to indicate a specific condition in a circuit. Red Pilot Light Green Pilot Light

Motor Running

Motor Stopped

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PLC Scan

A complete execution cycle of a programmable logic controller. The PLC scan involves taking in new inputs, executing the user program, performing diagnostic and communication functions, and generating new outputs. The PLC scan is repetitively executed.

Plug-in Busway

Busway that incorporates plug-in units to allow loads to be distributed over the length of the run.

Potentiometer

A type of variable resistor. Often referred to as a pot.

Power

The rate at which work is done or energy is transformed. In an electric circuit, power is measured in watts or sometimes in horsepower. The term power is also often used loosely to refer to electrical energy.

Power Circuit Breaker

A circuit breaker, characterized by large frame sizes and high short time ratings, which is used in switchgear or switchboards, and whose open construction allows for easy inspection, maintenance, and replacement of current carrying and operating parts. Available for low and medium voltage systems.

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Power Factor

The ratio of true power to apparent power in a circuit. Power factor is also equal to the cosine of the phase angle.

Pressure Switch

A control device that opens or closes its contacts in response to a change in the pressure of a liquid or gas.

Programmable Logic Controller (PLC)

A type of industrial computer used to control machines and processes. The PLC accepts inputs from switches and sensors and uses these inputs together with other data and program logic to control output devices.

Proportional-IntegralDerivative (PID) Control

A closed-loop control technique that seeks to minimize error by reacting to three values. One that is proportional to the error, one that is representative of the error over time, and one that is representative of the rate of change of the error.

Proximity Sensor

A type of sensing switch that detects the presence or absence of an object without physical contact.

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Pulse Width Modulation (PWM)

As applied to variable frequency drives, this is a technique for controlling the voltage applied to an AC motor by varying the pulse width while also controlling the frequency of the pulses. Current Increases Hysteresis Band

Current Decreases Sine Wave Reference

IGBT Turned On

IGBT Turned Off

On Off IGBT On Progressively Longer

IGBT On Progressively Shorter

Pushbutton

A control device used to manually open and close a set of contacts.

Random Access Memory (RAM)

Usually refers to a type of semiconductor memory often used for temporary storage because it requires the continual application of power to retain information. For some systems, battery backup is used to prevent data or program loss in the event of a power outage.

Reactance

The opposition to alternating current resulting from circuit inductance and capacitance. The symbol for reactance is “X.” The unit for reactance is the ohm.

Reactive Power

Power associated with inductance or capacitance. The unit for reactive power is the var.

Read Only Memory (ROM)

Usually refers to a type of semiconductor memory often used for permanent storage of data or programs that do not change.

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Rectifier

A device or circuit that converts alternating current to direct current.

Reduced-Voltage Controller

A type of motor starter that applies less than the full-line voltage to a three-phase induction motor while it is starting. A variety of types of reduced-voltage controllers exist including solid-state starters.

Resistance

A property of a material or circuit to oppose current flow. Resistance is symbolized by “R” and is measured in ohms.

Resistance Temperature Detector (RTD)

A device used to sense temperature that varies in resistance as temperature changes.

Resistor

A device manufactured to have a specific amount of resistance.

Resolver

An angular position sensing device that utilizes a rotating transformer with two secondary windings arranged at right angles to each other to provide angular position information. The amplitude of the wave induced into each stator winding depends on the angular position of the rotor winding. Since the amplitude variations available at the stator windings are 90° apart, one is called a sine signal and the other is called a cosine signal.

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Root-mean-square or RMS Value

The effective value of a current or voltage. Root-mean-square is descriptive of the mathematical process used to calculate the effective value of a periodic current or voltage.

Rotor

The rotating elements of the magnetic circuit of a rotating machine such as a motor.

Safety Switch

A switch mounted in an enclosure. Fusible enclosed switches include provisions for fuses in the enclosure.

Secondary Unit Substation

A coordinated design consisting of one or more transformers mechanically and electrically linked to switchgear or switchboard assemblies with an outgoing voltage rated below 1000 volts.

Selective Coordination

Applying circuit breakers in a manner that will minimize the extent of an outage in the event of a fault. Circuit breakers are typically installed in a branching arrangement. In the event of a fault, the breaker electrically closest to the fault should trip first. This can be accomplished by properly sizing and adjusting all breakers.

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Selector Switch

A control device with two or more positions used to manually open and close contacts.

Semiconductor

A special type of material with more resistance than a conductor, but less than that of an insulator. Semiconductors can be manufactured to produce devices such as diodes, transistors, thyristors, etc.

Transistor

Diode

Sensing Switch

A device, often called a sensor, used to provide information on the presence or absence of an object. Examples include a limit switch, photoelectric sensor, inductive proximity sensor, capacitive proximity sensor, and ultrasonic proximity sensor.

Serial Communication

Intelligent devices, such as computers, communicate with each other by sending bits of data in a series of binary signals to each other. RS-232 and RS-485 are specifications commonly used in serial communication.

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Service Entrance

The place where power is brought into a building. Also used to describe equipment at the service entrance.

Transformer

Service Entrance Load Center

Meter

Service Factor

A numerical value that is multiplied by a motor’s rated horsepower to determine the maximum horsepower at which the motor should be operated.

Service Head

A device used to connect busway at the service entrance.

Service Section

The switchboard section connected to incoming power.

Servo Drive

Usually refers to an electronic device used to control the speed and torque of a servo motor as part of a closed-loop positioning control system.

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Servo Motor

A motor designed with the dynamic response required for closed-loop positioning applications.

Set Point

The value used by a control circuit as desired value of a process variable.

Short Circuit

A normally unintended low resistance path for current.

Shunt Trip

A device used to remotely trip a circuit breaker. Shunt Trip

Shunt Trip

Single Quadrant Operation

Describes the operation of a variable speed drive that can provide torque to drive the motor, but cannot provide braking torque.

Slip

In a three-phase induction motor, slip is the difference between the synchronous speed and the rotor speed and is often expressed as a percentage. % Slip =

Solid-State

NS - NR NS

x 100

Used to describe equipment that contains semiconductor devices in an electronic circuit.

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Speed-Torque Curve

A graphical representation of the torque provided by a motor over a range of speeds. 300 275 250

Breakdown Torque

225

200 Locked Rotor Torque 175 150 125

Pull Up Torque

100 75

Full-Load Torque

50 Slip

25 0

0

10 20 30 40 50 60 70 80 90 100

% Synchronous Speed Rotor Speed

Splice Plates, Splice Bars

Plates used to join the horizontal bus bars of adjoining switchboard or motor control center sections.

Starter Ratings

Motor Starters are rated according to size and type of load. NEMA and IEC rate motor starters differently. IEC-rated devices are rated according to maximum operational current. NEMA specifies sizes from size 00 to size 9.

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Stator

The stationary elements of the magnetic circuit of a rotating machine such as a motor.

Step-down Transformer

A transformer with more turns of wire in its primary coil than in its secondary coil. The step-down transformer is used to step down the primary voltage to a lower secondary voltage. 2:1

Primary Coil 1800 turns

Secondary Coil 900 turns

120 VAC Out 10 amps

240 VAC Supply 5 amps

Step-up Transformer

A transformer with fewer turns of wire in its primary coil than in its secondary coil. The step-up transformer is used to step up the primary voltage to a higher secondary voltage. 1:2

Primary Coil 900 turns

120 VAC Supply 10 amps

Secondary Coil 1800 turns

240 VAC Out 5 amps

Surge

A transient increase in current and voltage.

Surge Protection

Used to describe equipment designed to prevent or limit damage resulting from a surge, provided that the surge does not exceed the capabilities of the protection devices.

109

Switchboard

A large panel or assembly of panels containing switches, overcurrent protective devices, buses, and associated instruments.

Switchgear

A coordinated design consisting of switching and interrupting devices and associated equipment such as control and protective devices and metering.

Synchronous Speed

The speed of the rotating magnetic field in a three-phase motor. Synchronous speed is determined by the line frequency and the number of motor poles.

Tachometer

A device used to provide a feedback signal representative of the speed of a rotating machine. Some tachometers are analog devices. Others provide a digital signal.

110

Thermal-Magnetic

Used to describe a device that uses both heat and magnetism as part of its operating principles. For example, a thermalmagnetic circuit breaker can be tripped either by heat or magnetic force resulting from excessive current.

Thermistor

A device used to sense temperature that varies in resistance as temperature changes.

Thermocouple

A device composed of two types of metal that produces a small voltage representative of the temperature at some point in a process.

Thyristor

A family of multi-layer semiconductor devices that includes silicon controlled rectifiers (SCR), triacs, and gate turnoff (GTO) thyristors. Thyristors are often used in rectifier or power switching circuits.

111

Time-Current Curve

A graph showing how long before a circuit breaker will trip at each level of fault current.

Timing Relay

A control device that opens or closes its contacts after a time delay. Some timing relays begin the time delay when the relay is energized. Others begin the time delay when the relay is deenergized.

Torque

A turning or twisting force. Since torque is expressed as a force times the length of the radius at which the force is measured, torque is represented in compound units such as pound-feet (lb.-ft.) Force 10 Lb

Radius 1 Foot Torque = 10 lb-ft

112

Total Harmonic Distortion (THD)

The ratio of harmonic distortion to the fundamental frequency. The greater the THD the more distortion there is.

Totally Enclosed Fan Cooled (TEFC)

A motor enclosure type that restricts the flow of air into or out of the motor, but uses a fan to blow air over the motor’s exterior. Fan

Totally Enclosed Non-ventilated (TENV)

A motor enclosure type that restricts the flow of air into or out of the motor.

Totally Integrated Automation (TIA)

A strategy developed by Siemens that emphasizes the seamless integration of automation products.

113

Transducer

A device that converts energy from one form to another. Often refers to sensing devices used to monitor or control a process.

Transformer

Coils of wire wound on a common frame that allow electrical energy to be transferred from one circuit to another.

Primary Coil

Secondary Coil

Transistor

A semiconductor device which usually has three terminals although the names of the terminals are different for different types of transistors. Some types of transistors are used as electronic switches.

Trim

The front cover of a panel, often including an access door.

Trip Unit

The part of the circuit breaker that can be manually or electronically set to determine under what conditions its contacts will automatically open.

114

True Power

Also called real power, true power is power dissipated by circuit 2 resistance. True power is equal to I R and is measured in watts. True power is also equal to the apparent power multiplied by the power factor.

Ultrasonic Sensor

A type of sensing switch that uses high frequency sound to detect the presence of an object without coming into contact with the object.

Underwriter’s Laboratory (UL)

A private company that is nationally recognized as an independent testing laboratory. UL tests products for safety. Products that pass UL tests can carry a UL label. UL has several categories of labels based upon the type of product tested.

Unit Substation

A coordinated design consisting of one or more transformers mechanically and electrically linked to switchgear or switchboard assemblies.

Var

The basic unit for reactive power. Shortened from volt-ampere reactive.

Variable Frequency Drive (VFD)

An electronic device used to control the speed and torque of an AC motor. Also called an AC drive. Converter

DC Link

Inverter

L1

L2

L3

C1

Control Logic

L1

3Ø Motor

115

Variable Speed Drive

An electronic drive device to control the speed and torque of either an AC or DC motor. Also called an adjustable speed drive.

Vector Control

Describes a technique employed by some variable frequency drives that uses a complex mathematical model of a motor to provide excellent control of speed and torque.

Volt

The basic unit of voltage. The symbol for volt is “V.”

Voltage

Also called difference of potential, electromotive force, or emf. Voltage is a force that when applied to a conductor causes current to flow. Voltage is symbolized by “E” or “V” and is measured in volts.

Voltmeter

A meter designed to measure voltage.

Volts per Hertz (V/Hz) Operation

Describes the operation of many variable frequency drives that control the speed of an AC motor by varying the frequency of the voltage applied to the motor while attempting to maintain a voltage to frequency ratio.

Watt

The basic unit of electric power. The symbol for watt is “W.”

116

Watt-Hour Meter

A meter designed to measure electrical energy usage.

Word

Usually one or more bytes used to represent instructions or data in digital equipment.

Wye

A connection arrangement used for the primary and/or secondary of a three-phase transformer.

117

Review Answers

Review 1

1) generator; 2) step-up; 3) 120; 4) 120; 5) Lateral service; 6) six; 7) surge arrester; 8) GFCI.

Review 2

1) C; 2) TPS; 3) distribution; 4) SMM; 5) 4000.

Review 3

1) low; 2) 16.5; 3) SR; 4) transformer; 5) Feeder.

Review 4

1) b; 2) c; 3) 24; 4) SINUMERIK®.

Review 5

1) Reduced voltage; 2) drive; 3) PROFIBUS; 4) ASI; 5) batch; 6) Closed-loop.

118

Final Exam


1.

The most efficient way to transmit energy from a power company to the utility’s customer via transmission lines is to ______ . a. b. c. d.

2.

The National Electrical Code® requires ______ for all branch circuits that supply 125-volt, single-phase, 15- and 20-amp receptacle outlets installed in dwelling unit bedrooms. a. b. c. d.

3.

Arc Fault Circuit Interrupters Circuit Breaker/Surge Arresters Ground Fault Circuit Interrupters TPS

______ is a motor starter manufactured by Siemens. a. b.

4.

Increase voltage and current Increase voltage and reduce current Decrease voltage and increase current Decrease voltage and current

TIASTAR S7-200

c. d.

INNOVA PLUS™ SINUMERIK®

According to the National Electrical Code® (NEC®), ______ may be accessible from the rear as well as the front. a. b. c. d.

load centers panelboards switchboards all of the above


119

5.

______ is a product used in Siemens busway, panelboards, switchboards, and switchgear to protect electrical equipment from damage due to electrical surges. a. b.

6.

ACCESS TIA

c. d.

PROFIBUS SIMATIC®

GFCI Single-pole NXAIR P Type RL

HMI TPS

c. d.

SITOP® Sentron™

distribute power throughout a building provide precise control for machine tools control lighting in a large commercial building control above NEMA motors

______ is a LAN used primarily at the device level. a. b.

120

TPS SMM

SINUMERIK® CNC models, such as 810D, 840Di, and 840D are Siemens products used to ______ . a. b. c. d.

11.

c. d.

______ is a trade name for Siemens regulated power supplies. a. b.

10.

MMS SPB

______ is a type of circuit breaker used in Siemens low voltage switchgear. a. b. c. d.

9.

GFCI GMI

______ is the trade name for the Siemens power management and control system. a. b.

8.

c. d.

Type _____ switchboards are commercial metering switchboards designed to meet west coast utility specifications. a. b.

7.

TPS PROFIBUS

Ethernet ASI

c. d.

PROFIBUS DP PROFIBUS PA

12.

______ is an alternative approach to distributed control systems (DCS) used for process control. a. b. c. d.

13.

______ refers to any device that acts as a link between the operator and the machine. a. b.

14.

MMS HMI

NXAIR P SIRIUS

c. d.

SIMATIC®HMI TIASTAR

for 480 volts for 1000 volts or less greater than 1000 to 100,000 volts greater than 100,000 to 230,000 volts

Which of the following is an HMI product? a. b. c. d.

17.

c. d.

Medium voltage equipment is rated ______ . a. b. c. d.

16.

SMM AWG

_______ is the trade name for a Siemens motor control center. a. b.

15.

SIMATIC® PCS 7 Closed-loop control WinCC® PROFIBUS SMS

AC motor WinCC® Switchboard Motor starter

______ is a control technique that compares a feedback signal representative of an actual value with a desired value and responds to minimize the error. a. b. c. d.

Open-loop control Closed-loop control Discrete control Continuous control

121

18.

Standards that correspond to a motor’s speed and torque characteristics are published by ______. a. b.

19.

c. d.

ISA NEC®

The ______ publishes the National Electrical Code®. a. b. c. d.

20.

NEMA UL

National Electrical Manufacturers Association Underwriter Laboratories, Inc. National Fire Protection Association Institute of Electrical and Electronic Engineers

_______ is the trade name of one type of medium voltage switchgear manufactured by Siemens that features an “arc vented” design. a. b. c. d.

RCIII 5 - 15 kV 38 KV NXAIR P


122

Notes

123



124

Table of Contents

Introduction ..............................................................................2 Residential Distribution.............................................................4 Load Centers ............................................................................7 Load Center Construction....................................................... 10 Overcurrent Protection ...........................................................22 Circuit Breakers ......................................................................25 Ground Fault Protection ..........................................................34 Arc Fault Protection ................................................................37 Surge Protection .....................................................................39 Types of Load Centers ............................................................44 Load Center Ratings ...............................................................47 Individual Overcurrent Protection ...........................................50 Service Entrance/Equipment Load Centers ............................52 Load Center Grounding...........................................................55 Power Supply Systems ...........................................................59 Siemens Small EQ Load Centers............................................62 Siemens Ultimate Load Centers.............................................65 Siemens Large EQ Load Centers ...........................................66 Meter Sockets, Meter Mains, and Meter Combinations.........68 Catalog Numbers....................................................................72 Sizing the Load Center ...........................................................75 Determining the Number of Circuits.......................................80 Review Answers.....................................................................87 Final Exam ..............................................................................88

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Load Centers and related products. Upon completion of Load Centers you should be able to:

2

•

Explain the role of a load center in residential distribution

•

Distinguish between the terms panelboard and load center

•

Define a load center (panelboard)

•


•

Identify various components of a Siemens load center

•

Distinguish between a main breaker and main lug only load center

•

Identify various power supply systems used in residential applications

•

Explain the use of load centers used as service-entrance equipment

•

Describe the proper grounding techniques of service entrance and downstream panelboards

•

Describe the proper use of GFCI and AFCI circuit breakers in a load center

•

Describe the proper use of the circuit breaker surge arrester in a load center

•

Identify various ratings of Siemens load centers

This knowledge will help you better understand customer applications. In addition, you will be able to describe products to customers and determine important differences between products. You should complete Basics of Electricity and Molded Case Circuit Breakers before attempting Load Centers. An understanding of many of the concepts covered in Basics of Electricity and Molded Case Circuit Breakers is required for Load Centers. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. INSTA-WIRE is a trademark of Siemens Energy & Automation, Inc. I-T-E, EQ and Speedfax are registered trademarks of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-2002, National Electrical Code® Copyright, 2001, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories Inc., and UL are registered trademarks of Underwriters Laboratories, Inc., Northbrook, IL 60062. The abbreviation “UL” is understood to mean Underwriter’s Laboratories, Inc. Other trademarks are the property of their respective owners.

3

Residential Distribution

A distribution system is a system that distributes electrical power throughout a building. Distribution systems are used in every residential, commercial, and industrial building. Residential Distribution

4

Most of us are familiar with the distribution system found in the average home. Power, purchased from a utility company, enters the house through a metering device.

The incoming power then goes to a load center which provides circuit control and overcurrent protection. The power is distributed from the load center to various branch circuits for lighting, appliances and electrical outlets. Careful planning is required so that the distribution system safely and efficiently supplies adequate electric service for present and possible future needs.

5

The National Electrical Code®

The National Electrical Code® (NEC®) is used extensively in the electrical industry. Throughout this course various articles of the NEC® will be referred to. You are encouraged to become familiar with this material as well as local building codes which are often more stringent than the NEC®.


6

Load Centers

The term “load center” is an industry term used to identify a panelboard used in certain applications. Load centers are typically rated 225 amps or less and 240 volts maximum and are intended for use in residential applications. NEC® and UL, however, make no distinction between a panelboard and a load center. Rules and definitions that apply to panelboards also apply to load centers.

7

Load Center Definition

The National Electrical Code® defines a load center (panelboard) as a single panel or group of panel units designed for assembly in the form of a single panel; including buses, automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front (Article 100-definitions). According to the NEC® definition, load centers (panelboards) are: • • • •

Used to control light, heat, or power circuits Placed in a cabinet or cutout box Mounted in or against a wall Accessible only from the front


8

Review 1 1.

A ____________ system distributes electrical power throughout a building.

2.

Load centers are covered by NEC® Article ____________ .

3.

Overcurrent protection is covered by NEC® Article ____________ .

4.

The National Electrical Code® makes no distinction between a panelboard and a load center. a. true b. false

5.

Which of the following does not meet the NEC® definition of a load center (panelboard). a. Used to control light, heat, or power circuits b. Placed in a cabinet or cutout box c. Accessible from the front or back d. Mounted in or against a wall

9

Load Center Construction

There are several components that make up a load center. Load centers consist of an enclosure, interior, and trim. Enclosure

The enclosure is typically constructed of cold rolled (for indoor use) or galvanized steel (for outdoor use) and houses the other components. It is designed to provide component and personnel protection. Knockouts are provided to allow the user to install conduit or cabling as required. Approved cable clamps or conduit hubs are used in the holes to secure and protect the cable and conductors.

NEMA Enclosures

The National Electrical Manufacturers Association (NEMA) and UL have established guidelines for electrical equipment enclosures. NEMA Type 1 enclosure are intended for indoor use. NEMA Type 3R enclosures are intended for outdoor use primarily to provide a degree of protection against rain, sleet and damage from external ice formation.

10

Removing Knockouts

Required knockouts may be removed prior to mounting the enclosure. On multiple ring knockouts remove the center section by striking at the point furthest from the tie. Bend the knockout back and forth to break the tie.

If a larger opening is required, remove each additional ring one at a time by prying with a screwdriver and bending back and forth with pliers as shown in the following figure.

11

Interior

The interior consists of several components, including bus bars and neutral bars. Branch circuit breakers are field added at the time of installation.

Bus Bars

A bus bar serves as a common connection for two or more circuits. It is represented schematically by a straight line with a number of connections made to it. Siemens load center bus bars are made with tin plated aluminum or copper.

12

Circuit Identification

Bus bars are required to have phases in sequence so that an installer can have the same fixed phase arrangement in each termination point in any panelboard or switchboard. This is established by NEMA and UL. It is assumed that bus bars are arranged according to NEMA and UL standards unless otherwise marked. The following diagram illustrates accepted NEMA and UL phase arrangements.

Neutral Bus*

An insulated neutral bus (which may be grounded/bonded) is provided in the load center. The neutral is a current-carrying component that is connected to the third wire of a singlephase, three-wire system or the fourth wire of a three-phase, four-wire system. For example, the following illustration shows the secondary of a 240 volt, single-phase transformer with a center tap. There are 240 volts between phases and 120 volts between phase A or B and neutral (N).

*Technically the “grounded circuit conductor” . 13

Split Neutral

In most instances the neutral bus is a split neutral, meaning that neutral connections are available on both sides of the load center. Split neutrals are connected together through a neutral tie bar.

INSTA-WIRE™

INSTA-WIRE is a feature found in Siemens load centers and circuit breakers up to 50 amps. The INSTA-WIRE screw is a backed-out screw retained in place by a special feature on the screw thread. This feature prevents the screw from falling out during shipment. The INSTA-WIRE screw head will accept either a standard screwdriver or a square tool bit. The INSTA-WIRE feature saves an installer time by eliminating the need to back out every screw and by allowing the installer to use a power tool to tighten screws.

14

Circuit Breakers

Circuit breakers mount directly to the bus bars. In the following illustration for example, a Type “QP” circuit breaker is mounted to the load center bus.

Label

The label identifies the load center’s catalog number, enclosure type, voltage rating, and ampacity. Additional information on the label identifies circuit breaker types that can be used with the load center, short circuit ratings, and wiring diagrams.

15

Trim Assembly

16

The trim assembly (dead front) is the front portion of the load center that covers the interior. The trim includes an access door and an adjustable upper pan. The trim/door provides access to the overcurrent devices while sealing off live parts and internal wiring from contact.

Twistouts

Part of the upper pan contains twistouts. These are used to cover any unused pole spaces not filled by a circuit breaker. Twistouts are removed by an up and down twisting motion with pliers. All unused openings in the upper pan must be filled with a filler plate.

Circuit Directory

A circuit directory (on the door), similar to one shown below, provides space for listing which breaker provides service for each room or large appliance.

17

Installation

18

The enclosure, with the interior, is mounted to a wall. All incoming and outgoing conductors are connected to the load center.

Siemens load centers can be surface or flush mounted. For flush mounted devices, the load center is positioned so that the front edge of the enclosure is flush with the finished wall. The trim assembly is installed after the wall is finished. All covers are combination covers unless surface or flush is specified.

19

NEC® Article 110.26

Load center installation requires careful planning to ensure a safe environment for personnel and equipment. Article 110.26 of the National Electrical Code® covers spaces about electrical equipment, such as load centers (panelboards). The intent of Article 110.26 is to provide enough working space for personnel to examine, adjust, service, and maintain energized equipment. Article 110.26 divides the three parts of a safe working space environment into depth, width, and height. In addition, Article 110.26 discusses entrance requirements to the working space as well as requirements for dedicated equipment space for indoor and outdoor applications. It is beyond the scope of this course to discuss in detail the requirements of Article 110.26. You are, however, encouraged to become familiar with it.


20

Review 2 1.

The two types of NEMA enclosures available for Siemens load centers are NEMA Type ___________ and NEMA Type ____________ .

2.

A ____________ ____________ serves as a common connection for two or more circuits.

3.

____________ circuit breakers are field added at the time of installation.

4.

A ____________ ____________ is a neutral connection that provides neutral connections on either side of the load center.

5.

____________ is an installation feature where screws are backed out and retained in place to prevent the screws from falling out.

6.

The ____________ assembly provides access to the overcurrent devices while sealing off the bus bars and internal wiring from contact.

7.

A ____________ ____________ provides space for listing which breaker provides service for each room or large appliance.

21

Overcurrent Protection

Load centers use circuit breakers to provide protection against overcurrent. The National Electrical Code® defines overcurrent as any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault (Article 100-definitions). Current flow in a conductor always generates heat. The greater the current flow, the hotter the conductor. Excess heat is damaging to electrical components. For that reason, conductors have a rated continuous current carrying capacity or ampacity. Overcurrent protection devices are used to protect conductors from excessive current flow. These protective devices are designed to keep the flow of current in a circuit at a safe level to prevent the circuit conductors from overheating.

22

Circuit protection would be unnecessary if overloads and short circuits could be eliminated. Unfortunately, overloads and short circuits do occur. To protect a circuit against these currents, a protective device must determine when a fault condition develops and automatically disconnect the electrical equipment from the voltage source. Slight overcurrents can be allowed to continue for a short time, but as the current magnitude increases, the protection device must open faster. Short circuits must be interrupted instantly. Circuit Breakers

The National Electrical Code® defines a circuit breaker as a device designed to open and close a circuit by nonautomatic means, and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. Circuit breakers provide a manual means of energizing and deenergizing a circuit. In addition, circuit breakers provide automatic overcurrent protection of a circuit. A circuit breaker allows a circuit to be reactivated after a short circuit or overload is cleared. Unlike fuses which must be replaced when they open, a simple push of the handle to the “Off” then “On” position restores the circuit. If a circuit reopens upon reset to the “On” position, a qualified electrician should be consulted to determine the problem.


23

Ampere Rating

Every circuit breaker has a specific ampere, voltage, and fault current interruption rating. The ampere rating defines the maximum current a circuit breaker can carry without tripping. Siemens residential circuit breakers are available with ratings from 15-125 amps.

Voltage Rating

Each circuit breaker is also rated for the maximum voltage it can handle. In residential applications, single-pole breakers protect 120 volt branch circuits; two-pole breakers protect 240 volt branch circuits. Siemens residential circuit breakers have a voltage rating of 120/240 volts. The rating of a circuit breaker can be higher than the circuit voltage, but never lower.

Short Circuit Interrupting Rating

The circuit breaker’s short circuit interrupting rating is the maximum available fault current which a breaker is designed to interrupt. Siemens residential circuit breakers have interrupting ratings from 10,000 amps to 65,000 amps. The available fault current is rarely above 10,000 amps in single-family homes.

Poles

Pole describes the number of isolated circuits that can pass through the circuit breaker at one time. A 1-pole circuit breaker can carry the current through one circuit. A 2-pole circuit breaker can carry the current through two circuits simultaneously. The two circuits are mechanically connected so that they open or close at the same time.

24

Circuit Breakers

Main Circuit Breaker

It is important to note the difference between a main breaker and branch circuit breakers. The main breaker of a load center shuts off power to the entire load center and all circuits supplied by that load center. The main circuit breaker has the same rating as the load center.

25

Branch Circuit Breakers

26

Branch circuit breakers provide protection for each branch circuit conductor in the distribution system. Typical branch circuits: •

15 and 20 ampere, 120 volt supply power for lighting circuits and electrical outlets

•

20 ampere, 120 volt supply power for some kitchen and bath electrical outlets

•

Appliances requiring larger amounts of power, such as clothes dryers, ranges, furnaces and air conditioners use separate branch circuit breakers rated for the appropriate voltage and current

Siemens manufactures several circuit breakers for use in branch circuits. These include 1-pole, 2-pole, duplex, triplex, quadplex, surge arrester, AFCI, and GFCI circuit breakers. Surge arrester, AFCI, and GFCI circuit breakers are speciality circuit breakers and will be discussed individually.

27

Full-Size Breakers

A full-size, 1-pole breaker requires one space (1”) and a full-size, 2-pole breaker requires two spaces (2”). If a 16-space load center were selected, 16 full-size 1-pole breakers, 8 full-size 2-pole breakers, or a combination of 1- and 2-pole breakers in a combination that does not exceed 16 spaces can be used.

1- and 2-Pole, Full-Sized Circuit Breakers

Siemens 1- and 2-pole circuit breakers are available with the following ratings.

28

Dual Breakers

In most cases only full-size breakers are used. There are times, however, when extra branch circuits are needed but all spaces are used. Some Siemens load centers are designed to accept dual breakers. A dual breaker is two breakers in a housing that has the same dimensions of a full-size, 1-pole breaker.

In a 16 space/32 circuit load center, 16 circuits are available if full-sized 1-pole circuit breakers are used. In a 16 space/32 circuit load center, 32 circuits are available if dual 1-pole breakers are used.

29

Circuit Limiting

Duplex circuit breakers can be used with load centers that have notched bus stabs. A rejection tab on the circuit breaker prevents the circuit breaker from being installed on a load center with unnotched tabs. This is referred to as circuit limiting. The number of notched tabs in a load center is limited by UL requirements. This limits the number of circuits available and helps prevent a load center from being overloaded. Special duplex circuit breakers are available that are not circuit limiting. These circuit breakers do not have a rejection tab and are designed for use on load centers built prior to 1965 when circuit limitations were introduced. These circuit breakers are referred to as non-circuit limiting.

Triplex, Quadplex Breakers

Siemens also offers triplex and quadplex circuit breakers. Triplex circuit breakers provide a 2-pole common trip breaker for 120/240 VAC circuits and two single poles for 120 VAC circuits. Quadplex breakers provide two sets of handle-tied, two-pole breakers for 120/240 VAC circuits. Both triplex and quadplex breakers require two panel spaces.

30

Catalog Numbers

To help identify each type of circuit breaker a catalog number is assigned. The catalog number provides a description of the circuit breaker, including voltage, amps, interruption rating, number of poles, and type.

Standard Breakers

31

Dual and Quad Breakers

32

Review 3 1.

Current flow in a conductor always generates ____________ .

2.

Pole describes the number of ____________ circuits that can pass through the circuit breaker at one time.

3.

The ____________ circuit breaker shuts off power to the entire load center and all circuits supplied by that load center.

4.

A ____________ breaker is two breakers in a housing that has the same dimensions of a full-size, 1-pole breaker.

5.

The number of duplex breakers that can be used in a load center is limited by UL. This is known as ____________ ____________ .

6.

Triplex and quadplex circuit breakers require ____________ panel spaces.

33

Ground Fault Protection

A ground fault occurs when a current-carrying conductor comes in contact with ground. A faulty appliance or the presence of water in contact with a conductor are two possible ways a ground fault can occur. One way ground fault protection is accomplished is by the use of GFCI receptacles. These are installed in place of a normal receptacle. Another way is with a GFCI circuit breaker such as the Siemens Type QPF GFCI circuit breakers. Any receptacle connected to the same circuit as the QPF GFCI circuit breaker is ground fault protected. A ground fault circuit interrupter (GFCI) compares current on the hot wire with current returning on the neutral wire. Under normal circumstances the current is equal.

34

When a ground fault occurs some of the current will return to the source through ground. In the following illustration, for example, a ground fault has occurred in a common household appliance. Anyone coming in contact with the appliance will become part of the circuit. The sensing and test circuit will detect that the amount of current returning on the neutral is less than the current on the hot wire. The sensing and test circuit will cause the trip coil to automatically open the circuit breaker, removing power from the appliance. GFCI devices trip between 4 to 6 milliamps. The amount of time it takes for a GFCI device to trip depends on the current. The higher the current the faster the device will trip.

Areas Requiring GFCI

Circuits providing power to certain areas of the home require ground fault circuit interrupters (GFCI). NEC® Article 210.8 describes the requirements for location of GFCIs. Ground fault protection is required on the following circuits: • • • • • • •

Bathroom receptacles Residential garage receptacles Outdoor receptacles Receptacles in unfinished basements Receptacles in crawl spaces Receptacles within six feet of a kitchen or bar sink Pools


35

Installing GFCI Breakers

36

GFCI type circuit breakers have one white neutral lead which is connected to the neutral bus in the load center. The phase and load neutral are connected to lugs in the GFCI. They mount in the load center in the same way as a standard circuit breaker.

Arc Fault Protection

AFCI vs GFCI

GFCI devices are designed to protect a person from getting a shock when touching an ungrounded appliance. Arc Fault Circuit Interrupters (AFCI), in comparison, protect against a fire being started from an unintended arc. An arc fault occurs when a current-carrying conductor has an arching condition to ground or another conductor. Damaged insulation, for example, can lead to an arc fault, which may not generate enough fault current to trip a circuit breaker. In the following example a staple has been driven through the insulation of a wire during installation.

37

AFCI Circuit Breaker

An AFCI device is intended to provide protection from the effects of arc faults by recognizing the characteristics unique to arcing and de-energizing the circuit when an arc fault is detected. The arc generated will cause the AFCI to trip. Arcs normally generated from electric equipment such as a light switch or power drill will not cause the AFCI to trip.

NEC® Article 210.12

Arc-Fault Circuit Interrupter protection was first introduced in the 1999 National Electrical Code®. NEC® Article 210.12 and has an effective date of 2002. This requirement applies to all branch circuits that supply 125-volt, single-phase, 15- and 20-amp receptacle outlets installed in dwelling unit bedrooms.

38

Surge Protection

Today’s homes have many semiconductor-based devices such as televisions, VCRs, stereos, computers and microwave ovens. These devices are highly susceptible to voltage spikes. Devices used in the home which generate voltage spikes include vacuum cleaners and other motor driven devices, and spark igniters on gas ranges, furnaces and water heaters. The most damaging voltage spikes are caused by lighting strikes. A lighting strike on a power line several miles away still has the potential to cause extensive electrical damage in a home. Lightning strikes on high voltage lines are generally dissipated by utility transmission and arresters. The average home, however, will experience eight to ten voltage surges of 1,000 to 10,000 volts annually. Damage to expensive electrical equipment can be instantaneous or cumulative.

39

Thunderstorms

A typical lightning strike consists of 25,000 amps at 30 million volts. The following map shows the approximate mean annual number of days with thunderstorms in the United States.

Siemens Circuit Breaker Surge Arrester

An electrical surge, whether it is caused by electrical equipment or lightning, always seeks ground. Any component between the source of the surge and ground can be damaged. Siemens circuit breaker surge arresters provide a preferred route to ground, bypassing expensive and sensitive equipment.

40

Installation

Installation is as simple as mounting a conventional circuit breaker in a Siemens load center. After power is switched off and the trim removed, the circuit breaker/surge arrestor plugs into place. A lead wire is provided to connect the ground side of the module to the load center’s neutral bus. It is best to position the circuit breaker/surge arrestor in the first position of the load center and connect the lead wire in the first neutral position. One device provides protection for the electrical system. Two red LEDs indicate that the device is working. The device does not require a dedicated space and can be added on to existing Siemens load centers. The circuit breaker portion of the surge arrester can be used on noncritical lighting circuits to provide additional visual indication that the device is working. If the device trips due to a high voltage surge, it is reset like any other circuit breaker in the panel.

41

Clamping Voltage

Clamping voltage is the amount of voltage allowed across a surge suppression device when it is conducting a specific current created by a surge. The clamping voltage of the Siemens surge arrestor is 600 volts at 1500 amps, and 800 volts at 5000 amps.

Peak Current Rating

Peak current rating specifies the maximum energy that can be dissipated from a single surge without causing the protecting device to sacrifice itself. The Siemens surge arrestor can withstand impulse currents as high as 40,000 amps, and energy levels as high as 960 joules line-to-line

.

42

Review 4 1.

A ground fault occurs when a current-carrying conductor comes in contact with ____________ .

2.

The NEC® does not require GFCI protection in which of the following areas? a. Bathroom receptacles b. Living room receptacles c. Outdoor receptacles d. Pools

3.

An arc fault condition occurs when a current-carrying conductor has an arching condition to ____________ or another conductor.

4.

The NEC® requires AFCI in ____________ receptacles.

5.

A typical lightning strike consists of ____________ amps.

6.

Siemens circuit breaker surge arresters are best installed in the ____________ position of a load center.

7.

Siemens surge arresters can withstand impulse currents as high as ____________ amps.


43

STEP 2000

Basics of PLCs

Table of Contents

Introduction ..............................................................................2 PLCs .........................................................................................4 Number Systems......................................................................8 Terminology ............................................................................ 14 Basic Requirements................................................................23 S7-200 Micro PLCs.................................................................28 Connecting External Devices..................................................39 Programming A PLC ...............................................................41 Discrete Inputs/Outputs .........................................................49 Analog Inputs and Outputs.....................................................61 Timers.....................................................................................64 Counters ................................................................................. 71 High-Speed Instructions .........................................................75 Specialized Expansion Modules .............................................78 Review Answers.....................................................................84 Final Exam ..............................................................................85

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Basics of PLCs and related products. Upon completion of Basics of PLCs you should be able to:

2

•

Identify the major components of a PLC and describe their functions

•

Convert numbers from decimal to binary, BCD, and hexadecimal

•

Identify typical discrete and analog inputs and outputs

•

Read a basic ladder logic diagram and statement list

•

Identify operational differences between different S7-200 models

•

Identify the proper manual to refer to for programming or installation of an S7-200 PLC

•

Connect a simple discrete input and output to an S7-200

•

Select the proper expansion module for analog inputs and outputs

•

Describe the operation of timers and counters

This knowledge will help you better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. You should complete Basics of Electricity before attempting Basics of PLCs. An understanding of many of the concepts covered in Basics of Electricity is required for Basics of PLCs. In addition you may wish to complete Basics of Control Components. Devices covered in Basics of Control Components are used with programmable logic controllers. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. SIMATIC, STEP 7, STEP 7-Micro, STEP 7-Micro/WIN, PG 702, and PG 740 are registered trademarks of Siemens Energy & Automation, Inc. Other trademarks are the property of their respective owners.

3

PLCs

Programmable Logic Controllers (PLCs), also referred to as programmable controllers, are in the computer family. They are used in commercial and industrial applications. A PLC monitors inputs, makes decisions based on its program, and controls outputs to automate a process or machine. This course is meant to supply you with basic information on the functions and configurations of PLCs.

4

Basic PLC Operation

PLCs consist of input modules or points, a Central Processing Unit (CPU), and output modules or points. An input accepts a variety of digital or analog signals from various field devices (sensors) and converts them into a logic signal that can be used by the CPU. The CPU makes decisions and executes control instructions based on program instructions in memory. Output modules convert control instructions from the CPU into a digital or analog signal that can be used to control various field devices (actuators). A programming device is used to input the desired instructions. These instructions determine what the PLC will do for a specific input. An operator interface device allows process information to be displayed and new control parameters to be entered.

Pushbuttons (sensors), in this simple example, connected to PLC inputs, can be used to start and stop a motor connected to a PLC through a motor starter (actuator).

5

Hard-Wired Control

Prior to PLCs, many of these control tasks were solved with contactor or relay controls. This is often referred to as hardwired control. Circuit diagrams had to be designed, electrical components specified and installed, and wiring lists created. Electricians would then wire the components necessary to perform a specific task. If an error was made the wires had to be reconnected correctly. A change in function or system expansion required extensive component changes and rewiring.

M

OL T1

M

OL T2

M

OL T3

L1 460 VAC L2 L3

Motor

OL M

1 CR

24 VAC Stop

Start CR

2

CR

Advantages of PLCs

The same, as well as more complex tasks, can be done with a PLC. Wiring between devices and relay contacts is done in the PLC program. Hard-wiring, though still required to connect field devices, is less intensive. Modifying the application and correcting errors are easier to handle. It is easier to create and change a program in a PLC than it is to wire and rewire a circuit. Following are just a few of the advantages of PLCs:

• • • • • •

6

Smaller physical size than hard-wire solutions. Easier and faster to make changes. PLCs have integrated diagnostics and override functions. Diagnostics are centrally available. Applications can be immediately documented. Applications can be duplicated faster and less expensively.

Siemens PLCs

Siemens makes several PLC product lines in the SIMATIC® S7 family. They are: S7-200, S7-300, and S7-400.

S7-200

The S7-200 is referred to as a micro PLC because of its small size. The S7-200 has a brick design which means that the power supply and I/O are on-board. The S7-200 can be used on smaller, stand-alone applications such as elevators, car washes, or mixing machines. It can also be used on more complex industrial applications such as bottling and packaging machines.

S7-300 and S7-400

The S7-300 and S7-400 PLCs are used in more complex applications that support a greater number of I/O points. Both PLCs are modular and expandable. The power supply and I/O consist of separate modules connected to the CPU. Choosing either the S7-300 or S7-400 depends on the complexity of the task and possible future expansion. Your Siemens sales representative can provide you with additional information on any of the Siemens PLCs.

7

Number Systems

Since a PLC is a computer, it stores information in the form of On or Off conditions (1 or 0), referred to as binary digits (bits). Sometimes binary digits are used individually and sometimes they are used to represent numerical values. Decimal System

Various number systems are used by PLCs. All number systems have the same three characteristics: digits, base, weight. The decimal system, which is commonly used in everyday life, has the following characteristics: Ten digits Base Weights

Binary System

0, 1, 2, 3, 4, 5, 6, 7, 8, 9 10 1, 10, 100, 1000, ...

The binary system is used by programmable controllers. The binary system has the following characteristics: Two digits Base Weights

0, 1 2 Powers of base 2 (1, 2, 4, 8, 16, ...)

In the binary system 1s and 0s are arranged into columns. Each column is weighted. The first column has a binary weight of 0 2 . This is equivalent to a decimal 1. This is referred to as the least significant bit. The binary weight is doubled with each succeeding column. The next column, for example, has a weight 1 of 2 , which is equivalent to a decimal 2. The decimal value is doubled in each successive column. The number in the far left hand column is referred to as the most significant bit. In this 7 example, the most significant bit has a binary weight of 2 . This is equivalent to a decimal 128.

8

Converting Binary to Decimal

The following steps can be used to interpret a decimal number from a binary value. 1) 2) 3)

Search from least to most significant bit for 1s. Write down the decimal representation of each column containing a 1. Add the column values.

In the following example, the fourth and fifth columns from the right contain a 1. The decimal value of the fourth column from the right is 8, and the decimal value of the fifth column from the right is 16. The decimal equivalent of this binary number is 24. The sum of all the weighted columns that contain a 1 is the decimal number that the PLC has stored.

In the following example the fourth and sixth columns from the right contain a 1. The decimal value of the fourth column from the right is 8, and the decimal value of the sixth column from the right is 32. The decimal equivalent of this binary number is 40.

Bits, Bytes, and Words

Each binary piece of data is a bit. Eight bits make up one byte. Two bytes, or 16 bits, make up one word.

9

Logic 0, Logic 1

Programmable controllers can only understand a signal that is On or Off (present or not present). The binary system is a system in which there are only two numbers, 1 and 0. Binary 1 indicates that a signal is present, or the switch is On. Binary 0 indicates that the signal is not present, or the switch is Off.

BCD

Binary-Coded Decimal (BCD) are decimal numbers where each digit is represented by a four-bit binary number. BCD is commonly used with input and output devices. A thumbwheel switch is one example of an input device that uses BCD. The binary numbers are broken into groups of four bits, each group representing a decimal equivalent. A four-digit thumbwheel switch, like the one shown here, would control 16 (4 x 4) PLC inputs.

10

Hexadecimal

Hexadecimal is another system used in PLCs. The hexadecimal system has the following characteristics: 16 digits Base Weights

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F 16 Powers of base 16 (1, 16, 256, 4096 ...)

The ten digits of the decimal system are used for the first ten digits of the hexadecimal system. The first six letters of the alphabet are used for the remaining six digits. A = 10 B = 11 C = 12

D = 13 E = 14 F = 15

The hexadecimal system is used in PLCs because it allows the status of a large number of binary bits to be represented in a small space such as on a computer screen or programming device display. Each hexadecimal digit represents the exact status of four binary bits. To convert a decimal number to a hexadecimal number the decimal number is divided by the base of 16. To convert decimal 28, for example, to hexadecimal:

Decimal 28 divided by 16 is 1 with a remainder of 12. Twelve is equivalent to C in hexadecimal. The hexadecimal equivalent of decimal 28 is 1C. The decimal value of a hexadecimal number is obtained by multiplying the individual hexadecimal digits by the base 16 weight and then adding the results. In the following example the hexadecimal number 2B is converted to its decimal equivalent of 43. 0

16 = 1 1 16 = 16 B = 11

11

Conversion of Numbers

12

The following chart shows a few numeric values in decimal, binary, BCD, and hexadecimal representation.

Review 1 1.

Identify the following:

2.

The binary number system has a base ____________ .

3.

The hexadecimal number system has a base ____________ .

4.

Convert a decimal 10 to the following: Binary

____________

BCD

____________

Hexadecimal

____________

13

Terminology

The language of PLCs consists of a commonly used set of terms; many of which are unique to PLCs. In order to understand the ideas and concepts of PLCs, an understanding of these terms is necessary. Sensor

A sensor is a device that converts a physical condition into an electrical signal for use by the PLC. Sensors are connected to the input of a PLC. A pushbutton is one example of a sensor that is connected to the PLC input. An electrical signal is sent from the pushbutton to the PLC indicating the condition (open/ closed) of the pushbutton contacts.

Actuators

Actuators convert an electrical signal from the PLC into a physical condition. Actuators are connected to the PLC output. A motor starter is one example of an actuator that is connected to the PLC output. Depending on the output PLC signal the motor starter will either start or stop the motor.

14

Discrete Input

A discrete input, also referred to as a digital input, is an input that is either in an ON or OFF condition. Pushbuttons, toggle switches, limit switches, proximity switches, and contact closures are examples of discrete sensors which are connected to the PLCs discrete or digital inputs. In the ON condition a discrete input may be referred to as a logic 1 or a logic high. In the OFF condition a discrete input may be referred to as a logic 0 or a logic low.

A Normally Open (NO) pushbutton is used in the following example. One side of the pushbutton is connected to the first PLC input. The other side of the pushbutton is connected to an internal 24 VDC power supply. Many PLCs require a separate power supply to power the inputs. In the open state, no voltage is present at the PLC input. This is the OFF condition. When the pushbutton is depressed, 24 VDC is applied to the PLC input. This is the ON condition.

15

Analog Inputs

An analog input is an input signal that has a continuous signal. Typical analog inputs may vary from 0 to 20 milliamps, 4 to 20 milliamps, or 0 to 10 volts. In the following example, a level transmitter monitors the level of liquid in a tank. Depending on the level transmitter, the signal to the PLC can either increase or decrease as the level increases or decreases.

Discrete Outputs

A discrete output is an output that is either in an ON or OFF condition. Solenoids, contactor coils, and lamps are examples of actuator devices connected to discrete outputs. Discrete outputs may also be referred to as digital outputs. In the following example, a lamp can be turned on or off by the PLC output it is connected to.

16

Analog Outputs

An analog output is an output signal that has a continuous signal. The output may be as simple as a 0-10 VDC level that drives an analog meter. Examples of analog meter outputs are speed, weight, and temperature. The output signal may also be used on more complex applications such as a current-topneumatic transducer that controls an air-operated flow-control valve.

CPU

The central processor unit (CPU) is a microprocessor system that contains the system memory and is the PLC decisionmaking unit. The CPU monitors the inputs and makes decisions based on instructions held in the program memory. The CPU performs relay, counting, timing, data comparison, and sequential operations.

17

Programming

A program consists of one or more instructions that accomplish a task. Programming a PLC is simply constructing a set of instructions. There are several ways to look at a program such as ladder logic, statement lists, or function block diagrams.

Ladder Logic

Ladder logic (LAD) is one programming language used with PLCs. Ladder logic uses components that resemble elements used in a line diagram format to describe hard-wired control. Refer to the STEP 2000 course Basics of Control Components for more information on line diagrams.

STEP 2000

Basics of Control Components

Ladder Logic Diagram

18

The left vertical line of a ladder logic diagram represents the power or energized conductor. The output element or instruction represents the neutral or return path of the circuit. The right vertical line, which represents the return path on a hard-wired control line diagram, is omitted. Ladder logic diagrams are read from left-to-right, top-to-bottom. Rungs are sometimes referred to as networks. A network may have several control elements, but only one output coil.

In the example program shown example I0.0, I0.1 and Q0.0 represent the first instruction combination. If inputs I0.0 and I0.1 are energized, output relay Q0.0 energizes. The inputs could be switches, pushbuttons, or contact closures. I0.4, I0.5, and Q1.1 represent the second instruction combination. If either input I0.4 or I0.5 are energized, output relay Q0.1 energizes. Statement list

A statement list (STL) provides another view of a set of instructions. The operation, what is to be done, is shown on the left. The operand, the item to be operated on by the operation, is shown on the right. A comparison between the statement list shown below, and the ladder logic shown on the previous page, reveals a similar structure. The set of instructions in this statement list perform the same task as the ladder diagram.

Function Block Diagrams

Function Block Diagrams (FBD) provide another view of a set of instructions. Each function has a name to designate its specific task. Functions are indicated by a rectangle. Inputs are shown on the left-hand side of the rectangle and outputs are shown on the right-hand side. The function block diagram shown below performs the same function as shown by the ladder diagram and statement list.

19

PLC Scan

The PLC program is executed as part of a repetitive process referred to as a scan. A PLC scan starts with the CPU reading the status of inputs. The application program is executed using the status of the inputs. Once the program is completed, the CPU performs internal diagnostics and communication tasks. The scan cycle ends by updating the outputs, then starts over. The cycle time depends on the size of the program, the number of I/Os, and the amount of communication required.

Software

Software is any information in a form that a computer or PLC can use. Software includes the instructions or programs that direct hardware.

Hardware

Hardware is the actual equipment. The PLC, the programming device, and the connecting cable are examples of hardware.

20

Memory Size

Kilo, abbreviated K, normally refers to 1000 units. When talking about computer or PLC memory, however, 1K means 1024. This 10 is because of the binary number system (2 =1024). This can be 1024 bits, 1024 bytes, or 1024 words, depending on memory type.

RAM

Random Access Memory (RAM) is memory where data can be directly accessed at any address. Data can be written to and read from RAM. RAM is used as a temporary storage area. RAM is volatile, meaning that the data stored in RAM will be lost if power is lost. A battery backup is required to avoid losing data in the event of a power loss.

ROM

Read Only Memory (ROM) is a type of memory that data can be read from but not written to. This type of memory is used to protect data or programs from accidental erasure. ROM memory is nonvolatile. This means a user program will not lose data during a loss of electrical power. ROM is normally used to store the programs that define the capabilities of the PLC.

EPROM

Erasable Programmable Read Only Memory (EPROM) provides some level of security against unauthorized or unwanted changes in a program. EPROMs are designed so that data stored in them can be read, but not easily altered. Changing EPROM data requires a special effort. UVEPROMs (ultraviolet erasable programmable read only memory) can only be erased with an ultraviolet light. EEPROM (electronically erasable programmable read only memory), can only be erased electronically.

Firmware

Firmware is user or application specific software burned into EPROM and delivered as part of the hardware. Firmware gives the PLC its basic functionality.

21

Putting it Together

The memory of the S7-200 is divided into three areas: program space, data space, and configurable parameter space.

• Program space stores the ladder logic (LAD) or statement list (STL) program instructions. This area of memory controls the way data space and I/O points are used. LAD or STL instructions are written using a programming device such as a PC, then loaded into program memory of the PLC.

• Data space is used as a working area, and includes memory locations for calculations, temporary storage of intermediate results and constants. Data space includes memory locations for devices such as timers, counters, high-speed counters, and analog inputs and outputs. Data space can be accessed under program control.

• Configurable parameter space, or memory, stores either the default or modified configuration parameters.

22

Basic Requirements

In order to create or change a program, the following items are needed:

• • • •

PLC

PLC Programming Device Programming Software Connector Cable

Throughout this course we will be using the S7-200 because of its ease of use.

23

Programming Devices

The program is created in a programming device (PG) and then transferred to the PLC. The program for the S7-200 can be created using a dedicated Siemens SIMATIC S7 programming device, such as a PG 720 (not shown) or PG 740, if STEP 7 Micro/WIN software is installed.

A personal computer (PC), with STEP 7 Micro/WIN installed, can also be used as a programming device with the S7-200.

24

Software

A software program is required in order to tell the PLC what instructions it must follow. Programming software is typically PLC specific. A software package for one PLC, or one family of PLCs, such as the S7 family, would not be useful on other PLCs. The S7-200 uses a Windows based software program called STEP 7-Micro/WIN32. The PG 720 and PG 740 have STEP 7 software pre-installed. Micro/WIN32 is installed on a personal computer in a similar manner to any other computer software.

Connector Cables PPI (Point-to-Point Interface)

Connector cables are required to transfer data from the programming device to the PLC. Communication can only take place when the two devices speak the same language or protocol. Communication between a Siemens programming device and the S7-200 is referred to as PPI protocol (pointto- point interface). An appropriate cable is required for a programming device such as a PG 720 or PG 740. The S7-200 uses a 9-pin, D-connector. This is a straight-through serial device that is compatible with Siemens programming devices (MPI port) and is a standard connector for other serial interfaces.

Programming Device Cable

25

A special cable, referred to as a PC/PPI cable, is needed when a personal computer is used as a programming device. This cable allows the serial interface of the PLC to communicate with the RS-232 serial interface of a personal computer. DIP switches on the PC/PPI cable are used to select an appropriate speed (baud rate) at which information is passed between the PLC and the computer.

26

Review 2 1.

A switch or a pushbutton is a ____________ input.

2.

A lamp or a solenoid is an example of a ___________ output.

3.

The ____________ makes decisions and executes control instructions based on the input signals.

4.

____________ ____________ is a PLC programming language that uses components resembling elements used in a line diagram.

5.

A ____________ consists of one or more instructions that accomplish a task.

6.

Memory is divided into three areas: ____________ , ____________ , and ____________ ____________ space.

7.

When talking about computer or PLC memory, 1K refers to ____________ bits, bytes, or words.

8.

Software that is placed in hardware is called ____________ .

9.

Which of the following is not required when creating or changing a PLC program? a. b. c. d. e.

PLC Programming Device Programming Software Connector Cable Printer

10. A special cable, referred to as a ____________ cable, is needed when a personal computer is used as a programming device.

27

Basic Requirements

In order to create or change a program, the following items are needed:

• • • •

PLC

PLC Programming Device Programming Software Connector Cable

Throughout this course we will be using the S7-200 because of its ease of use.

23

Programming Devices

The program is created in a programming device (PG) and then transferred to the PLC. The program for the S7-200 can be created using a dedicated Siemens SIMATIC S7 programming device, such as a PG 720 (not shown) or PG 740, if STEP 7 Micro/WIN software is installed.

A personal computer (PC), with STEP 7 Micro/WIN installed, can also be used as a programming device with the S7-200.

24

Software

A software program is required in order to tell the PLC what instructions it must follow. Programming software is typically PLC specific. A software package for one PLC, or one family of PLCs, such as the S7 family, would not be useful on other PLCs. The S7-200 uses a Windows based software program called STEP 7-Micro/WIN32. The PG 720 and PG 740 have STEP 7 software pre-installed. Micro/WIN32 is installed on a personal computer in a similar manner to any other computer software.

Connector Cables PPI (Point-to-Point Interface)

Connector cables are required to transfer data from the programming device to the PLC. Communication can only take place when the two devices speak the same language or protocol. Communication between a Siemens programming device and the S7-200 is referred to as PPI protocol (pointto- point interface). An appropriate cable is required for a programming device such as a PG 720 or PG 740. The S7-200 uses a 9-pin, D-connector. This is a straight-through serial device that is compatible with Siemens programming devices (MPI port) and is a standard connector for other serial interfaces.

SF/DIAG


25

A special cable is needed when a personal computer is used as a programming device. Two versions of this cable are available. One version, called an RS-232/PPI Multi-Master Cable, connects a personal computer’s RS-232 interface to the PLC’s RS-485 connector. The other version, called a USB/PPI Multi-Master Cable, connects a personal computer’s USB interface to the PLC’s RS-485 connector.

26

Review 2 1.

A switch or a pushbutton is a ____________ input.

2.

A lamp or a solenoid is an example of a ___________ output.

3.

The ____________ makes decisions and executes control instructions based on the input signals.

4.

____________ ____________ is a PLC programming language that uses components resembling elements used in a line diagram.

5.

A ____________ consists of one or more instructions that accomplish a task.

6.

Memory is divided into three areas: ____________ , ____________ , and ____________ ____________ space.

7.

When talking about computer or PLC memory, 1K refers to ____________ bits, bytes, or words.

8.

Software that is placed in hardware is called ____________ .

9.

Which of the following is not required when creating or changing a PLC program? a. b. c. d. e.

PLC Programming Device Programming Software Connector Cable Printer

10. An RS-232/PPI Multi-Master cable or a USB/PPI-MultiMaster cable may be used to connect a personal computer to the PLC’s ____________ connector.

27

S7-200 Micro PLCs

The S7-200 Micro PLC is the smallest member of the SIMATIC S7 family of programmable controllers. The central processing unit (CPU) is internal to the PLC. Inputs and outputs (I/O) are the system control points. Inputs monitor field devices, such as switches and sensors. Outputs control other devices, such as motors and pumps. The programming port is the connection to the programming device.

S7-200 Models

There are five S7-200 CPU types: CPU 221, CPU 222, CPU 224, CPU 224XP, and CPU 226 and two power supply configurations for each type.

Model Description 221 DC/DC/DC 221 AC/DC/Relay 222 DC/DC/DC 222 AC/DC/Relay 224 DC/DC/DC 224 AC/DC/Relay 224XP DC/DC/DC

Power Supply 20.4-28.8 VDC 85-264 VAC, 47-63 Hz 20.4-28.8 VDC 85-264 VAC, 47-63 Hz 20.4-28.8 VDC 85-264 VAC, 47-63 Hz 20.4-28.8 VDC

Input Types 6 DC 6 DC 8 DC 8 DC 14 DC 14 DC 14 DC, 2 Analog

Output Types 4 DC 4 Relay 6 DC 6 Relay 10 DC 10 Relay 10 DC, 1 Analog

224XP AC/DC/Relay

85-264 VAC, 47-63 Hz

14 DC, 2 Analog 10 Relay, 1 Analog

226 DC/DC/DC 226 AC/DC/Relay

20.4-28.8 VDC 85-264 VAC, 47-63 Hz

24 DC 24 DC

16 DC 16 Relay

The model description indicates the type of CPU, the power supply, the type of input, and the type of output.

28

S7-200 Features

The S7-200 family includes a wide variety of CPUs and features. This variety provides a range of features to aid in designing a cost-effective automation solution. The following table provides a summary of the major features, many of which will be covered in this course.

Feature Memory

CPU 221

CPU 222

CPU 224

CPU 224XP

CPU 226

Program (with run mode edit)

4096 Bytes

4096 Bytes

8192 Bytes

12288 Bytes

16384 Bytes

Program (w/o run mode edit)

4096 Bytes

4096 Bytes

12288 Bytes

16384 Bytes

24576 Bytes

User Data Memory Type Memory Cartridge Data Backup (super cap) Data Backup (opt. battery) I/O Local Digital I/O Local Analog I/O Max Expansion Modules Instructions Boolean Execution Speed Internal Relays Counters TImers Sequential Control Relays For/Next Loops Integer Math (+-*/) Floating-Point Math (+-*/) Enhanced Features

2048 Bytes EEPROM EEPROM 50 Hours 200 Days





6 In/4 Out None None

8 In/6 Out None 2

14 In/10 Out None 7

14 In/10 Out 2 In/1 Out 7

24 In/16 Out None 7

0.22 µs/Inst. 256 256 256 256 Yes Yes Yes





High-Speed Counters

4 (30 KHz)

4 (30 KHz)

6 (30 KHz)

Analog Adjustments Pulse Outputs (DC) Timed Interrupts Edge Interrupts Real-Time Clock Password Protection Communications Number of Ports

1 2 (20 KHz) 2 (1 - 255ms) 4 Optional Yes

1 2 (20 KHz) 2 (1 - 255ms) 4 Optional Yes

2 2 (20 KHz) 2 (1 - 255ms) 4 Built-In Yes

4 (30 KHz), 2 (200 KHz) 2 2 (100 KHz) 2 (1 - 255ms) 4 Built-In Yes

1 (RS-485) PPI, MPI, Freeport (NETR/NETW)



1 (RS-485) PPI, MPI, Protocols Supported Freeport Peer-to-Peer PPI Master Mode (NETR/NETW)

6 (30 KHz) 2 2 (20 KHz) 2 (1 - 255ms) 4 Built-In Yes 2 (RS-485) PPI, MPI, Freeport (NETR/NETW)

29

Mode Switch and Analog Adjustment

When the mode switch is in the RUN position the CPU is in the run mode and executing the program. When the mode switch is in the STOP position the CPU is stopped. When the mode switch is in the TERM position the programming device can select the operating mode. The analog adjustment is used to increase or decrease values stored in special memory. These values can be used to update the value of a timer or counter, or can be used to set limits.

Optional Cartridge

The S7-200 supports an optional memory cartridge that provides a portable EEPROM storage for your program. The cartridge can be used to copy a program from one S7-200 PLC to a like S7-200 PLC. In addition, two other cartridges are available. A real-time clock with battery is available for use on the CPU 221 and CPU 222. The battery provides up to 200 days of data retention time in the event of a power loss. The CPU 224, CPU 224XP and CPU 226 have a real-time clock built in. Another cartridge is available with a battery only.

SF/DIAG

30

Expansion Modules

The S7-200 PLCs are expandable. Expansion modules contain additional inputs and outputs. These are connected to the base unit using a ribbon connector.

The ribbon connector is protected by a cover on the base unit. Side-by-side mounting completely encloses and protects the ribbon connector.

31

Available Expansion

The CPU 221 comes with 6 digital inputs and 4 digital outputs. These are not expandable. The CPU 222 comes with 8 digital inputs and 6 digital outputs and will accept up to 2 expansion modules. The CPU 224 and CPU 224XP come with 14 digital inputs and 10 digital outputs and will accept up to 7 expansion modules. The S7-226 comes with 24 digital inputs and 16 digital outputs and will accept up to 7 expansion modules.

CPU221

Status Indicators

6 Inputs, 4 Outputs No Expansion Modules (EM) 8 Inputs, 6 Outputs Up to 2 Expansion Modules

CPU222

EM

EM

CPU224

EM

EM

EM

EM

EM

EM

EM

14 Inputs, 10 Outputs Up to 7 Expansion Modules

CPU224XP

EM

EM

EM

EM

EM

EM

EM

14 Inputs, 10 Outputs 2 Analog In, 1 Analog Out Up to 7 Expansion Modules

CPU226

EM

EM

EM

EM

EM

EM

EM

24 Inputs, 16 Outputs Up to 7 Expansion Modules

The CPU status indicators reflect the current mode of CPU operation. When the CPU is in the RUN mode, the green RUN indicator is lit. When the CPU is in the STOP mode, the yellow STOP indicator is lit. The System Fault/Diagnostic (SF/DIAG) indicator turns red for a system fault and yellow to indicate certain diagnostic conditions.

The I/O status indicators represent the On or Off status of corresponding inputs and outputs. For example, when the CPU senses an input is on, the corresponding green indicator is lit. 32

Installing

The S7-200 can be installed in one of two ways. A DIN clip allows installation on a standard DIN rail. The DIN clip snaps open to allow installation and snaps closed to secure the unit on the rail. The S7-200 can also be panel mounted using installation holes located behind the access covers.

External Power Supply Sources

An S7-200 can be connected to either a 24 VDC or a 120/230 VAC power supply depending on the CPU. An S7-200 DC/DC/ DC would be connected to a 24 VDC power supply.

24 VDC Power Supply

An S7-200 AC/DC/Relay would be connected to a 120 or 230 VAC power supply.

Neutral Ground

Line

33

I/O Numbering

S7-200 inputs and outputs are labeled at the wiring terminations and next to the status indicators. These alphanumeric symbols identify the I/O address to which a device is connected. This address is used by the CPU to determine which input is present and which output needs to be turned on or off. I designates a discrete input and Q designates a discrete output. The first number identifies the byte, the second number identifies the bit. Input I0.0, for example, is byte 0, bit 0. I0.0 = Byte 0, Bit 0 I0.1 = Byte 0, Bit 1 I1.0 = Byte 1, Bit 0 I1.1 = Byte 1, Bit 1 The following table identifies the input and output designations.

Inputs

Input devices, such as switches, pushbuttons, and other sensor devices are connected to the terminal strip under the bottom cover of the PLC.

Input Devices Connected Here

Pushbutton

34

Switch

Input Simulator

A convenient method of testing a program is to wire toggle switches to the inputs. Input simulators with prewired toggle switches are available for the S7-200s. Switches are wired between the 24 VDC power supply (L+) and the inputs. For example, the switch on the far left is wired between the first input (0.0) and L+. When the switch is closed, 24 VDC is applied to the input. This is referred to as a logic 1. When the switch is open, 0 VDC is applied to the input. This is referred to as a logic 0.

Outputs

Output devices, such as relays, are connected to the terminal strip under the top cover of the PLC. When testing a program, it is not necessary to connect output devices. The LED status indicators signal if an output is active.

Relay

Light

Output Devices Wired Here

From Input Power Supply

35

Optional Connector

An optional fan-out connector allows for field wiring connections to remain fixed when removing or replacing a CPU 221 or CPU 222. The appropriate connector slides into either the input, output, or expansion module terminals.

Removable Terminal Strip

The CPU 224, CPU 224XP, and CPU 226 do not have an optional fan-out connector. Instead, the terminal strips are removable. This allows the field wiring connections to remain fixed when removing or replacing the PLC.

36

Super Capacitor

A super capacitor, so named because of its ability to maintain a charge for a long period of time, protects data stored in RAM in the event of a power loss. The RAM memory is typically backed up on the CPU 221 and CPU 222 for 50 hours, and on the CPU 224, CPU 224 XP, and CPU 226 for 100 hours.

Reference Manual

The SIMATIC S7-200 Programmable Controller System Manual provides complete information on installing and programming the S7-200 PLCs.

37

Review 3 1.

The five models of S7-200 are ____________ , ____________ , ____________ , ____________, and ____________ .

2.

Which of the following is not available on an CPU 221? a. b. c. d.

38

Mode Switch Expansion Port Programming Port Status Indicators

3.

A CPU 222 can have a maximum of ____________ expansion modules and a CPU 224 can have a maximum of ____________ expansion modules.

4.

A CPU 222 has ____________ DC inputs and ____________ DC outputs without expansion modules.

5.

A CPU 224 has ____________ DC inputs and ____________ DC outputs without expansion modules.

6.

The fourth output of an S7-200 would be labeled ____________ .

7.

S7-200 can be panel mounted or installed on a ____________ rail.

Connecting External Devices

TD200

The S7-200 programming port can be used to communicate with a variety of external devices. One such device is the TD200 text display unit. The TD200 displays messages read from the S7-200, allows adjustment of designated program variables, provides the ability to force, and permits setting of the time and date. The TD200 can be connected to an external power supply or receive its power from the S7-200.

SF/DIAG


Freeport Mode

PPI Protocol

The programming port has a mode called freeport mode. Freeport mode allows connectivity to various intelligent sensing devices such as a bar code reader.

Bar-Code Decoder

Bar-Code Reader

Programming Port

RS-485 to RS-232 Interface

Freeport Mode

39

Printer

Freeport mode can also be used to connect to a non-SIMATIC printer. Freeport Mode

Programming Port

Connecting Cable

Serial to Parallel Converter

Interconnection

It is possible to use one programming device to address multiple S7-200 devices on the same communication cable. A total of 31 units can be interconnected without a repeater.

IBM or IBM Compatible PC

S7-200

S7-200

PPI Interconnection

40

S7-200

Programming a PLC

STEP 7-Micro/WIN32 is the program software used with the S7-200 PLC to create the PLC operating program. STEP 7 consists of a number of instructions that must be arranged in a logical order to obtain the desired PLC operation. These instructions are divided into three groups: standard instructions, special instructions, and high-speed instructions.

Standard Instructions

Standard instructions consists of instructions that are found in most programs. Standard instructions include: timer, counter, math, logical, increment/decrement/invert, move, and block instructions.

Special Instructions

Special instructions are used to manipulate data. Special instructions include: shift, table, find, conversion, for/next, and real-time instructions.

High-Speed Instructions

High-speed instructions allow for events and interrupts to occur independent of the PLC scan time. These include high-speed counters, interrupts, output, and transmit instructions. It is not the purpose of this text to explain all of the instructions and capabilities. A few of the more common instructions necessary for a basic understanding of PLC operation will be discussed. PLC operation is limited only by the hardware capabilities and the ingenuity of the person programming it. Refer to the SIMATIC S7-200 Programmable Controller System Manual for detailed information concerning these instructions.

41

Micro/WIN32

The programming software can be run Off-line or On-line. Offline programming allows the user to edit the ladder diagram and perform a number of maintenance tasks. The PLC does not need to be connected to the programming device in this mode. On-line programming requires the PLC to be connected to the programming device. In this mode program changes are downloaded to the PLC. In addition, status of the input/output elements can be monitored. The CPU can be started, stopped, or reset.

Symbols

In order to understand the instructions a PLC is to carry out, an understanding of the language is necessary. The language of PLC ladder logic consists of a commonly used set of symbols that represent control components and instructions.

Contacts

One of the most confusing aspects of PLC programming for first-time users is the relationship between the device that controls a status bit and the programming function that uses a status bit. Two of the most common programming functions are the normally open (NO) contact and the normally closed (NC) contact. Symbolically, power flows through these contacts when they are closed. The normally open contact (NO) is closed when the input or output status bit controlling the contact is 1. The normally closed contact (NC) is closed when the input or output status bit controlling the contact is 0.

42

Coils

Coils represent relays that are energized when power flows to them. When a coil is energized, it causes a corresponding output to turn on by changing the state of the status bit controlling that output to 1. That same output status bit may be used to control normally open and normally closed contacts elsewhere in the program.

Boxes

Boxes represent various instructions or functions that are executed when power flows to the box. Typical box functions are timers, counters, and math operations.

Entering Elements

Control elements are entered in the ladder diagram by positioning the cursor and selecting the element from a lists. In the following example the cursor has been placed in the position to the right of I0.2. A coil was selected from a pulldown list and inserted in this position.

Network 1 I0.0

I0.1

Q0.0

Network 2 I0.2

Cursor

43

An AND Operation

Each rung or network on a ladder represents a logic operation. The following programming example demonstrates an AND operation. Two contact closures and one output coil are placed on network 1. They were assigned addresses I0.0, I0.1, and Q0.0. Note that in the statement list a new logic operation always begins with a load instruction (LD). In this example I0.0 (input 1) and (A in the statement list) I0.1 (input 2) must be true in order for output Q0.0 (output 1) to be true. It can also be seen that I0.0 and I0.1 must be true for Q0.0 to be true by looking at the function block diagram representation.

Another way to see how an AND function works is with a Boolean logic diagram. In Boolean logic an AND gate is represented by a number of inputs on the left side. In this case there are two inputs. The output is represented on the right side. It can be seen from the table that both inputs must be a logic 1 in order for the output to be a logic 1. And (A) Function

And (A) Function Input 1

Output 1

Input 2 Input 1 0 0 1 1

44

Input 2 0 1 0 1

Output 1 0 0 0 1

I0.0

Q0.0

I0.1 I0.0 0 0 1 1

I0.1 0 1 0 1

Q0.0 0 0 0 1

An OR Operation

In this example an OR operation is used in network 1. It can be seen that if either input I0.2 (input 3) or (O in the statement list) input I0.3 (input 4), or both are true, then output Q0.1 (output 2) will be true.

Another way to see how an OR function works is with a Boolean logic diagram. The symbol differs slightly from an AND function. The OR function is represented by a number of inputs on the left side. In this case there are two inputs. The output is represented on the right side. It can be seen from the table that any input can be a logic 1 in order for the output to be a logic 1. Or (O) Function Input 3

Output 2

Input 4 Input 3 0 0 1 1

Or (O) Function

Input 4 0 1 0 1

Output 2 0 1 1 1

I0.4

Q0.1

I0.5 I0.4 0 0 1 1

I0.5 0 1 0 1

Q0.1 0 1 1 1

45

Testing a Program

Once a program has been written it needs to be tested and debugged. One way this can be done is to simulate the field inputs with an input simulator, such as the one made for the S7-200. The program is first downloaded from the programming device to the CPU. The selector switch is placed in the RUN position. The simulator switches are operated and the resulting indication is observed on the output status indicator lamps.

Status Functions

After a program has been loaded and is running in the PLC, the actual status of ladder elements can be monitored using STEP 7 Micro/WIN32 software. The standard method of showing a ladder element is by indicating the circuit condition it produces when the device is in the deenergized or non operated state. In the following illustration input 1 (I0.0) is programmed as a normally open (NO) contact. In this condition, power will not flow through the contacts to the output (Q0.0).

46

When viewing the ladder diagram in the status mode, control elements that are active, or true (logic 1), are highlighted. In the example shown the toggle switch connected to input 1 has been closed. Power can now flow through the control element associated with input 1 (I0.0) and activate the output (Q0.0). The lamp will illuminate.

Forcing

Forcing is another useful tool in the commissioning of an application. It can be used to temporarily override the input or output status of the application in order to test and debug the program. The force function can also be used to override discrete output points. The force function can be used to skip portions of a program by enabling a jump instruction with a forced memory bit. Under normal circumstances the toggle switch, shown in the illustration below, would have to be closed to enable input 1 (I0.0) and turn on the output light. Forcing enables input 1 even though the input toggle switch is open. With input 1 forced high the output light will illuminate. When a function is forced the control bit identifier is highlighted. The element is also highlighted because it is on.

47

The following table shows the appearance of ladder elements in the Off, forced, and On condition.

48

Discrete Inputs/Outputs

To understand discrete control of a programmable controller the same simple lamp circuit illustrated with forcing will be used. This is only for instructional purposes as a circuit this simple would not require a programmable controller. In this example the lamp is off when the switch is open and on when the switch is closed.

Wiring

To accomplish this task, a switch is wired to the input of the PLC and an indicator light is wired to output terminal.

Light

Switch

49

The following drawing illustrates the sequence of events. A switch is wired to the input module of the PLC. A lamp is wired to the output module. The program is in the CPU. The CPU scans the inputs. When it finds the switch open I0.0 receives a binary 0. This instructs Q0.0 to send a binary 0 to the output module. The lamp is off. When it finds the switch closed I0.0 receives a binary 1. This instructs Q0.0 to send a binary 1 to the output module, turning on the lamp.

Program Instruction

When the switch is open the CPU receives a logic 0 from input I0.0. The CPU sends a logic 0 to output Q0.0 and the light is off.

When the switch is closed the CPU receives a logic 1 from input I0.0. The CPU sends a logic 1 to output Q0.0, thus activating Q0.0. The light turns on.

50

Motor Starter Example

The following example involves a motor start and stop circuit. The line diagram illustrates how a normally open and a normally closed pushbutton might be used in a control circuit. In this example a motor started (M) is wired in series with a normally open momentary pushbutton (Start), a normally closed momentary pushbutton (Stop), and the normally closed contacts of an overload relay (OL).

Momentarily depressing the Start pushbutton completes the path of current flow and energizes the motor starter (M).

51

This closes the associated M and Ma (auxiliary contact located in the motor starter) contacts. When the Start button is released a holding circuit exists to the M contactor through the auxiliary contacts Ma. The motor will run until the normally closed Stop button is depressed, or the overload relay opens the OL contacts, breaking the path of current flow to the motor starter and opening the associated M and Ma contacts.

This control task can also be accomplished with a PLC.

Motor Starter (Actuator)

Output

Motor

PLC

Input

52

Start/Stop Pushbuttons (Sensors)

Program Instruction

A normally open Start pushbutton is wired to the first input (I0.0), a normally closed Stop pushbutton is wired to the second input (I0.1), and normally closed overload relay contacts (part of the motor starter) are connected to the third input (I0.2). The first input (I0.0), second input (I0.1), and third input (I0.2) form an AND circuit and are used to control normally open programming function contacts on Network 1. I0.1 status bit is a logic 1 because the normally closed (NC) Stop Pushbutton is closed. I0.2 status bit is a logic 1 because the normally closed (NC) overload relay (OL) contacts are closed. Output Q0.0 is also programmed on Network 1. In addition, a normally open set of contacts associated with Q0.0 is programmed on Network 1 to form an OR circuit. A motor starter is connected to output Q0.0.

When the Start pushbutton is depressed the CPU receives a logic 1 from input I0.0. This causes the I0.0 contact to close. All three inputs are now a logic 1. The CPU sends a logic 1 to output Q0.0. The motor starter is energized and the motor starts.

53

When the Start pushbutton is pressed, output Q0.0 is now true and on the next scan, when normally open contact Q0.0 is solved, the contact will close and output Q0.0 will stay on even if the Start pushbutton has been released.

The motor will continue to run until the Stop pushbutton is depressed. Input I0.1 will now be a logic 0 (false). The CPU will send a binary 0 to output Q0.0. The motor will turn off.

54

When the Stop pushbutton is released I0.1 logic function will again be true and the program ready for the next time the Start pushbutton is pressed.

Expanding the Application

The application can be easily expanded to include indicator lights for RUN and STOP conditions. In this example a RUN indicator light is connected to output Q0.1 and a STOP indicator light is connected to output Q0.2.


Output

Motor Indicator Lights

PLC

Input


55

It can be seen from the ladder logic that a normally open output Q0.0 is connected on Network 2 to output Q0.1 and a normally closed Q0.0 contact is connected to output Q0.2 on network 3. In a stopped condition output Q0.0 is off. The normally open Q0.0 contacts on Network 2 are open and the RUN indicator, connected to output Q0.1 light is off. The normally closed Q0.1 on Network 3 lights are closed and the STOP indicator light, connected to output Q0.2 is on.

56

When the PLC starts the motor output Q0.0 is now a logic high (On). The normally open Q0.0 contacts on Network 2 now switch to a logic 1 (closed) and output Q0.1 turns the RUN indicator on. The normally closed Q0.0 contacts on Network 3 switch to a logic 0 (open) and the STOP indicator light connected to output Q0.2 is now off.

Adding a Limit Switch

The application can be further expanded by adding a limit switch with normally open contacts to input I0.3.


Motor

Output

Indicator Lights

PLC

Input Limit Switch


57

A limit switch could be used to stop the motor or prevent the motor from being started. An access door to the motor, or its associated equipment, is one example of a limit switch’s use. If the access door is open, the normally open contacts of LS1 connected to input I0.3 are open and the motor will not start.

When the access door is closed, the normally open contacts on the limit switch (LS1) are closed. Input I0.3 is now on (logic 1), and the motor will start when the Start pushbutton is pressed.

58

Expansion

The PLC program can be expanded to accommodate many commercial and industrial applications. Additional Start/Stop pushbuttons and indicator lights can be added for remote operation, or control of a second motor starter and motor. Overtravel limit switches can be added along with proximity switches for sensing object position. In addition, expansion modules can be added to further increase the I/O capability. The applications are only limited by the number of I/Os and amount of memory available on the PLC.

Motor Starters (Digital Outputs)

Indicator Lights (Digital Outputs)

I/O Expansion Module

Pushbuttons (Digital Inputs)

Sensors (Digital Inputs)

59

Review 4 1.

Identify the following symbols:

a. ____________

b. ____________ c. ____________

60

2.

Complete the following tables:

3.

In the following instruction Q0.0 will be true (logic 1) when ____________ or ____________ is true, and when ____________ is true.

Analog Inputs and Outputs

PLCs must also work with continuous or analog signals. Typical analog signals are 0 - 10 VDC or 4 - 20 mA. Analog signals are used to represent changing values such as speed, temperature, weight, and level. A PLC cannot process these signals in an analog form. The PLC must convert the analog signal into a digital representation. An expansion module, capable of converting the analog signal, must be used. The S7-200 analog modules convert standard voltage and current analog values into a 12-bit digital representation. The digital values are transferred to the PLC for use in register or word locations. In addition, analog modules are available for use with thermocouple and RTD type sensors used in to achieve a high level of accuracy in temperature measurement.

SF/DIAG

Analog Expansion Module

61

Application Example

A field device that measures a varying value is typically connected to a transducer. In the following example a scale is connected to a load cell. A load cell is a device that takes a varying value and converts it to a variable voltage or current output. In this example the load cell is converting a value of weight into a 0 - 10 VDC output. The output value depends entirely on the manufactured specifications for the device. This load cell outputs 0 - 10 VDC for a 0 - 500 Lbs input. The 0 - 10 VDC load cell output is connected to the input of an analog expansion module.

The example application can be expanded to include a conveyor system with a gate to direct packages of varying weight. As packages move along the conveyor they are weighed. A package that weighs at or greater than a specified value is routed along one conveyor path. A package that weighs less than a specified value is routed along another conveyor path, where it will later be inspected for missing contents.

62

Analog Outputs

Analog outputs are used in applications requiring control capability of field devices which respond to continuous voltage or current levels. Analog outputs may be used as a variable reference for control valves, chart recorders, electric motor drives, analog meters, and pressure transducers. Like analog inputs, analog outputs are generally connected to a controlling device through a transducer. The transducer takes the voltage signal and, depending on the requirement, amplifies, reduces, or changes it into another signal which controls the device. In the following example a 0 - 10 VDC signal controls a 0 - 500 Lbs. scale analog meter.

63

Timers

Timers are devices that count increments of time. Traffic lights are one example where timers are used. In this example timers are used to control the length of time between signal changes.

Timers are represented by boxes in ladder logic. When a timer receives an enable, the timer starts to time. The timer compares its current time with the preset time. The output of the timer is a logic 0 as long as the current time is less than the preset time. When the current time is greater than the preset time the timer output is a logic 1. S7-200 uses three types of timers: OnDelay (TON), Retentive On-Delay (TONR), and Off-Delay (TOF).

64

S7-200 Timers

S7-200 timers are provided with resolutions of 1 millisecond, 10 milliseconds, and 100 milliseconds. The maximum value of these timers is 32.767 seconds, 327.67 seconds, and 3276.7 seconds, respectively. By adding program elements, logic can be programmed for much greater time intervals.

Hard-Wired Timing Circuit

Timers used with PLCs can be compared to timing circuits used in hard-wired control line diagrams. In the following example, a normally open (NO) switch (S1) is used with a timer (TR1). For this example the timer has been set for 5 seconds. When S1 is closed, TR1 begins timing. When 5 seconds have elapsed, TR1 will close its associated normally open TR1 contacts, illuminating pilot light PL1. When S1 is open, deenergizing TR1, the TR1 contacts open, immediately extinguishing PL1. This type of timer is referred to as ON delay. ON delay indicates that once a timer receives an enable signal, a predetermined amount of time (set by the timer) must pass before the timer’s contacts change state.

On-Delay (TON)

When the On-Delay timer (TON) receives an enable (logic 1) at its input (IN), a predetermined amount of time (preset time - PT) passes before the timer bit (T-bit) turns on. The T-bit is a logic function internal to the timer and is not shown on the symbol. The timer resets to the starting time when the enabling input goes to a logic 0.

65

In the following simple timer example, a switch is connected to input I0.3, and a light is connected to output Q0.1.

When the switch is closed input 4 becomes a logic 1, which is loaded into timer T37. T37 has a time base of 100 ms (.100 seconds). The preset time (PT) value has been set to 150. This is equivalent to 15 seconds (.100 x 150 ). The light will turn on 15 seconds after the input switch is closed. If the switch were opened before 15 seconds had passed, then reclosed, the timer would again begin timing at 0.

I0.3

T37 IN

150

T37

66

TON

PT

Q0.1

A small sample of the flexibility of PLCs is shown in the following program logic. By reprogramming the T37 contact as a normally closed contact, the function of the circuit is changed to cause the indicator light to turn off only when the timer times out. This function change was accomplished without changing or rewiring I/O devices.

I0.3

T37 IN

150

T37

Retentive On-Delay (TONR)

TON

PT

Q0.1

The Retentive On-Delay timer (TONR) functions in a similar manner to the On-Delay timer (TON). There is one difference. The Retentive On-Delay timer times as long as the enabling input is on, but does not reset when the input goes off. The timer must be reset with a RESET (R) instruction.

67

The same example used with the On-Delay timer will be used with the Retentive On-Delay timer. When the switch is closed at input I0.3, timer T5 (Retentive timer) begins timing. If, for example, after 10 seconds input I0.3 is opened the timer stops. When input I0.3 is closed the timer will begin timing at 10 seconds. The light will turn on 5 seconds after input I0.3 has been closed the second time. A RESET (R) instruction can be added. Here a pushbutton is connected to input I0.2. If after 10 seconds input I0.3 were opened, T5 can be reset by momentarily closing input I0.2. T5 will be reset to 0 and begin timing from 0 when input I0.3 is closed again. T5

I0.2

R

I0.3

T5 IN

150

The Off-Delay timer is used to delay an output off for a fixed period of time after the input turns off. When the enabling bit turns on the timer bit turns on immediately and the value is set to 0. When the input turns off, the timer counts until the preset time has elapsed before the timer bit turns off. TXXX IN

PT

68

PT

Q0.1

T5

Off-Delay (TOF)

TONR

TOF

S7-200 Timers

The S7-200s have 256 timers. The specific T number chosen for the timer determines its time base and whether it is TON, TONR, or TOF.

Timer Example

In the following example a tank will be filled with two chemicals, mixed, and then drained. When the Start Button is pressed at input I0.0, the program starts pump 1 controlled by output Q0.0. Pump 1 runs for 5 seconds, filling the tank with the first chemical, then shuts off. The program then starts pump 2, controlled by output Q0.1. Pump 2 runs for 3 seconds filling the tank with the second chemical. After 3 seconds pump 2 shuts off. The program starts the mixer motor, connected to output Q0.2 and mixes the two chemicals for 60 seconds. The program then opens the drain valve controlled by output Q0.3, and starts pump 3 controlled by output Q0.4. Pump 3 shuts off after 8 seconds and the process stops. A manual Stop switch is also provided at input I0.1.

69

Review 5

70

1.

Analog signals are converted into a ____________ format by the PLC.

2.

Three types of timers available in the S7-200 are OnDelay, ____________ On-Delay, and ____________Delay.

3.

The maximum time available on a 100 millisecond time base timer is ____________ seconds.

4.

A count of 25 on a 10 millisecond time base timer represents a time of __________ milliseconds.

5.

There are ____________ timers in the S7-200.

Counters

Counters used in PLCs serve the same function as mechanical counters. Counters compare an accumulated value to a preset value to control circuit functions. Control applications that commonly use counters include the following:

•

Count to a preset value and cause an event to occur

•

Cause an event to occur until the count reaches a preset value

A bottling machine, for example, may use a counter to count bottles into groups of six for packaging.

71

Counters are represented by boxes in ladder logic. Counters increment/decrement one count each time the input transitions from off (logic 0) to on (logic 1). The counters are reset when a RESET instruction is executed. S7-200 uses three types of counters: up counter (CTU), down counter (CTD), and up/down counter (CTUD). XXX

XXX

XXX

CTU

CTD

CTUD

CU

CD

R

LD

PV

PV

CD CU

Count Up

Count Down

R PV

Count Up/Down

S7-200 Counters

There are 256 counters in the S7-200, numbered C0 through C255. The same number cannot be assigned to more than one counter. For example, if an up counter is assigned number 45, a down counter cannot also be assigned number 45. The maximum count value of a counter is ±32,767.

Up Counter

The up counter counts up from a current value to a preset value (PV). Input CU is the count input. Each time CU transitions from a logic 0 to a logic 1 the counter increments by a count of 1. Input R is the reset. A preset count value is stored in PV input. If the current count is equal to or greater than the preset value stored in PV, the output bit (Q) turns on (not shown). XXX CTU CU

R PV

72

Down Counter

The down counter counts down from the preset value (PV) each time CD transitions from a logic 0 to a logic 1. When the current value is equal to zero the counter output bit (Q) turns on (not shown). The counter resets and loads the current value with the preset value (PV) when the load input (LD) is enabled. XXX CTD CD

LD PV

Up/Down Counter

The up/down counter counts up or down from the preset value each time either CD or CU transitions from a logic 0 to a logic 1. When the current value is equal to the preset value, the output QU turns on. When the current value (CV) is equal to zero, the output QD turns on. The counter loads the current value (CV) with the preset value (PV) when the load input (LD) is enabled. Similarly, the counter resets and loads the current value (CV) with zero when the reset (R) is enabled. The counter stops counting when it reaches preset or zero. XXX CTUD CD CU R LD PV

73

Counter Example

A counter might be used to keep track of the number of vehicles in a parking lot. As vehicles enter the lot through an entrance gate, the counter counts up. As vehicles exit the lot through an exit gate, the counter counts down. When the lot is full a sign at the entrance gate turns on indicating the lot is full.

Up/down counter C48 is used in this example. A switch, connected to the entrance gate, has been wired to input I0.0. A switch, connected to the exit gate, has been wired to input I0.1. A reset switch, located at the collection booth, has been wired to input I0.2. The parking lot has 150 parking spaces. This value has been stored in the preset value (PV). The counter output has been directed to output Q0.1. Output 2 is connected to a “Parking Lot Full” sign. As cars enter the lot the entrance gate opens. Input I0.0 transitions from a logic 0 to a logic 1, incrementing the count by one. As cars leave the lot the exit gate opens. Input I0.1 transitions from a logic 0 to a logic 1, decrementing the count by 1. When the count has reached 150 output Q0.1 transitions from a logic 0 to a logic 1. The “Parking Lot Full” sign illuminates. When a car exits, decrementing the count to 149, the sign turns off.

74

High-Speed Instructions

As discussed earlier, PLCs have a scan time. The scan time depends on the size of the program, the number of I/Os, and the amount of communication required. Events may occur in an application that require a response from the PLC before the scan cycle is complete. For these applications high-speed instructions can be used.

High-Speed Counters

High-speed counters are represented by boxes in ladder logic. CPU 221 and CPU 222 support four high-speed counters (HSC0, HSC3, HSC4, HSC5). CPU 224, CPU 224XP, and CPU 226 support six high-speed counters (HSC0, HSC1, HSC2, HSC3, HSC4, HSC5).

75

Definition Boxes and High-Speed Counters

The high-speed counter definition boxes are used to assign a mode to the counter. High-speed counters can be defined by the definition box to operate in any of the twelve available modes. It should be noted that not all counters can operate in all of the available modes. Refer to the S7-Programmable Controller System Manual for definitions available for each counter. Each counter has dedicated inputs for clocks, direction control, reset, and start where these functions are supported.

Positioning

Positioning is one example of an application that can use high-speed counters. In the following illustration a motor is connected through a starter to a PLC output. The motor shaft is connected to an encoder and a positioning actuator. The encoder emits a series of pulses as the motor turns. In this example the program will move an object from position 1 to position 6. Assume the encoder generates 600 pulses per revolution, and it takes 1000 motor revolutions to move the object from one position to another. To move the object from position 1 to position 6 (5 positions) would take 5000 motor revolutions. The counter would count up 30,000 counts (5000 revolutions x 600 pulses per revolution) and stop the motor. 0

Encoder

1

2

3

4

5

6

7

8

9 10

Motor Starter

Interrupts

Interrupts are another example of an instruction that must be executed before the PLC has completed the scan cycle. Interrupts in the S7-200 are prioritized in the following order: 1. Communications 2. I/O Interrupts 3. Time-Based Interrupts

76

PTO

Pulse Train Output (PTO) is used to provide a series of pulses to an output device, such as a stepper motor driver. The PTO provides a square wave output for a specified number of pulses and a specified cycle time. The number of pulses can be from 1 to 4,294,967,295 pulses. PTOs have a 50% duty cycle. This means the pulse is off for the same amount of time it is on. The number of pulses and the cycle time can be changed with an interrupt. In the following example each pulse is on for 500 ms, and off for 500 ms. After four pulses an interrupt occurs which changes the cycle time to 1000 ms.

Q0.0 4 Pulses 1000 milliseconds Each

4 Pulses 500 milliseconds Each Interrupt Occurs

PWM

The Pulse Width Modulation (PWM) function provides a fixed cycle time with a variable duty cycle time. When the pulse width is equal to the cycle time, the duty cycle is 100% and the output is turned on continuously. In the following example the output has a 10% duty cycle (on 10% off 90%). After an interrupt the cycle switches to a 50% duty cycle (on 50%, off 50%). On

Off

On

Off

Q0.0 10% Duty Cycle

50% Duty Cycle

The PWM function can be used to provide a programmable or adjustable control of machine timing. This allows machine operation to be varied to compensate for product variations or mechanical wear. Transmit

Transmit allows communication with external devices, such as modems, printers, computers, via the serial interface. See the section titled “Connecting External Devices” for examples.

77

Specialized Expansion Modules

In addition to I/O modules, expansion modules are available for the S7-200 that measure temperature, control positioning applications, and provide various communication functions. EM 241

In any complex system communication is essential. Modems are electronic devices used for sending and receiving data over long distances. The EM 241 is an expansion module that supports communication between an S7-200 PLC and STEP 7 Micro/WIN via a modem.

The EM 241 provides an international telephone line interface, supports sending numeric and text paging messages, as well as SMS (Short Message Service) messages to cellular phones. This is useful for remote diagnostics and maintenance, machine control, alarm systems, and general communication functions. In addition to CPU-to-CPU communication via a telephone line, the EM 241 also supports the ModBus RTU protocol. Protocols are rules that identify how devices should communicate with each other. ModBus RTU is a protocol originally developed by MODICON, which is now part of Schneider Automation. ModBus RTU has been widely used by other companies. CP 243-1, CP 243-1 IT

78

Industrial Ethernet provides a proven means of networking computers and a variety of intelligent devices. CP 243-1 and CP 243-1 IT are communication processors used to connect the S7-200 system to Industrial Ethernet.

Ethernet Communications

CP 243-1 Ethernet CP 243-1 IT Internet

The S7-200 can be remotely configured, programmed, and diagnosed via Industrial Ethernet using STEP 7 Micro/WIN. The S7-200 can also communicate with other S7-200, S7-300, and S7-400 PLCs and a variety of other devices using Industrial Ethernet. The IT functions of the CP 243-1 IT Internet module simplify the process of setting up a control system that can email diagnostic information or transfer files using Internet protocols. EM 277

Information flow between intelligent devices such as PLCs, computers, variable speed drives, actuators, and sensors is often accomplished through a local area network (LAN). LANs are used in office, manufacturing, and industrial areas. In the past, these networks were often proprietary systems designed to a specific vendor’s standards. Siemens has been a leader in pushing the trend to open systems based upon international standards developed through industry associations. PROFIBUS-DP and Actuator Sensor Interface (ASi) are examples of these open networks. The PROFIBUS-DP EM 277 module allows connection of the S7-200 CPU to a PROFIBUS-DP network as a slave. The CP 243-2 Communication Processor allows communication between AS-i devices and an S7-200.

79

PROFIBUS DP

PROFIBUS DP is an open bus standard for a wide range of applications in various manufacturing and automation processes. PROFIBUS DP works at the field device level such as power meters, motor protectors, circuit breakers, and lighting controls. Through PROFIBUS DP the features of S7-200 PLCs can be used to their full extent within a distributed system. An advantage to PROFIBUS DP is the ability to communicate between PROFIBUS DP devices of different vendors. This provides uniform communication between all SIMATIC devices on the PROFIBUS DP network as well as devices from other manufacturers.

AS-i

Actuator Sensor Interface (AS-i or AS-Interface) is a system for networking binary devices such as sensors. Until recently, extensive parallel control wiring was needed to connect sensors to the controlling device. AS-i replaces complex wiring with a simple 2-core cable. The cable is designed so that devices can only be connected correctly. Several devices can be connected to the cable.

80

PLCs, for example, use I/O modules to receive inputs from binary devices such as sensors. Binary outputs are used to turn on or off a process as the result of an input.

EM 253

Position control describes a range of applications that involve movement with varying degrees of precision. Rotary tables and traversing cars are examples where objects are moved from one position during a product’s manufacturing process.

The EM 253 is a positioning module that enables the user to control the speed and position for either stepper motors or servo motors. The EM 253 interfaces between an S7-200 PLC and the stepper/servo motor’s power control module. Control Actual Value Stepper Motor Power Module Servo/Stepper Servo Motor S7-200 with EM 253

81

EM 253 Features

Web Site

The EM 253 provides functionality for single-axis, open-loop position control. Features of the module include: •

High-speed control with a range of 12 - 200,000 pulse per second

•

Jerk (S curve) or linear acceleration/deceleration

•

Configurable measuring system to enter data as engineering units (such as inches or centimeters) or number of pulses

•

Configurable backlash compensation

•

Supports absolute, relative, and manual methods of position control

•

Continuous operation

•

Provides up to 25 motion profiles with up to 4 speed changes per profile

•

Four different reference-point seek modes, with a choice of the starting seek direction and final approach direction for each sequence

For more information and sales support on the S7-200 visit our web site at: http://www.automation.siemens.com/s7-200/index_76.htm.

82

Review 6 1.

The S7-200 supports ____________ counters.

2.

Three types of counters used in S7-200 are ____________ , ____________ , and ____________ .

3.

Counters can count to a maximum of ____________ .

4.

Events that require an action from the PLC before the scan cycle is complete are controlled by ____________ ____________ instructions.

5.

Depending on the counter, there are up to ____________ modes available on high-speed counters.

6.

The ____________ allows communication between AS-i devices and an S7-200.

7.

The ____________ is a position control module.

83

Review Answers

Review 1

1) a: input module, b: CPU, c: output module, d: programming device, e: operator interface; 2) 2; 3) 16; 4) 1010, 0001 0000, A.

Review 2

1) discrete; 2) discrete; 3) CPU; 4) Ladder logic; 5) program; 6) program, data, configuarable parameter; 7) 1024; 8) firmware; 9) e; 10) RS-485.

Review 3

1) 221, 222, 224, 224XP, 226; 2) b; 3) 2, 7; 4) 8, 6; 5) 14, 10; 6) Q0.3; 7) DIN.

Review 4

1) a: box, b: contact, c: coil; 2) AND Function - a: 0, b: 0, c: 0, d: 1, Or Function - e: 0, f: 1, g: 1, h: 1; 3) I0.0 or Q0.0, and I0.1.

Review 5

1) digital; 2) retentive, off; 3) 3276.7 seconds; 4) 250; 5) 256.

Review 6

1) 256; 2) CTU, CTD, CTUD; 3) ±32,767; 4) high-speed; 5) 12; 6) CP 243-2 Communication Processor; 7) EM 253.

84

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. After completing the test, mail the answer sheet in for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. 1.

The component of a PLC that makes decisions and executes control instructions based on the input signals is the ____________ . a. c.

2.

b. d.

8 bits 32 bits

11 101

d.

b. 111

100

analog high-speed

b. d.

discrete normally open

A programming language that uses symbols resembling elements used in hard-wired control line diagrams is referred to as a ____________ . a. c.

6.

2 bits 16 bits

An input that is either On or Off is a/an ____________ input. a. c.

5.

Input module Operator interface

The binary equivalent of a decimal 5 is ____________ . a. c.

4.

b. d.

One byte is made up of ____________ . a. c.

3.

CPU Programming device

ladder logic diagram network

b. d.

statement list PLC scan

A type of memory that can be read from but not written to is ____________ . a. c.

RAM firmware

b. d.

ROM K memory 85

7.

A USB/PPI Multi-Master cable connects a personal computer’s USB interface to a/an ____________ connector on an S7-200 CPU. a. c.

8.

b. d.

RS-232 PROFIBUS-DP

The CPU 224 AC/DC/RELAY has ____________ . a. b. c. d.

9.

RS-485 Ethernet

8 DC inputs and 10 relay outputs 8 AC inputs and 6 relay outputs 14 DC inputs and 14 relay outputs 14 DC inputs and 10 relay outputs

CPU 224 will accept up to ____________ expansion modules. a. c.

none 10

b. d.

7 30

10. The S7-222 has the ability to store ____________ kbytes in user data. a. c. 11.

4 2

b. d.

8 5

Which of the following is not part of a PLC scan? a. c.

Read Inputs Force Interrupts

b. d.

Execute Program Update Outputs

12. The address designation for output four of an S7-200 is ____________ . a. c.

I0.4 Q0.3

b. d.

I0.3 Q0.4

13. CPU 221 and CPU 222 provide ____________ high-speed counters . a. c.

two four

b. d.

three five

14. The maximum value of an S7-200 timer with a resolution of 1 millisecond is ____________ seconds. a. c. 86

3.2767 327.67

b. d.

32.767 3276.7

15. An S7-200 timer with a time base of 100 ms can count to a maximum value of ____________ seconds. a. c.

3.2767 327.67

b. d.

32.767 3276.7

16. The time base of TON 32 of is ____________ ms. a. c. 17.

.1 1

b. d.

10 100

The maximum count of an S7-200 up counter is ____________ . a. c.

32,767 98,301

b. d.

65,534 1,000,000

18. A/An ____________ is used to assign a mode to a highspeed counter. a. c.

toggle switch PLC scan

b. d.

interrupt definition box

19. ____________ instructions allows communication with external devices, such as modems, printers, and computers. a. c.

Transmit High-speed counters

b. d.

Interrupt High-speed outputs

20. ____________ is used to temporarily override the input or output status in order to test and debug the program. a. c.

Transmit Interrupt

b. d.

Forcing PLC scan

87



88

Table of Contents

Introduction ............................................................................. 2 Monitoring and Managing Electrical Power with ACCESS ...... 4 Electrical Power Distribution ................................................... 5 Voltage and Current Values ...................................................... 9 Changes in Voltage and Current ............................................ 16 Frequency and Harmonics ..................................................... 22 Power and Power Factor ........................................................ 27 ACCESS System ................................................................... 37 WinPM and SIEServe ............................................................ 38 Communication Protocols and Standards ............................. 41 Local Area Networks ............................................................. 44 Serial Communication ........................................................... 46 Power Metering ..................................................................... 54 Power Meter Features ........................................................... 63 Protective Relays and Trip Units ............................................ 66 Circuit Breaker Trip Units ....................................................... 68 SAMMS................................................................................. 72 S7 I/O Device ........................................................................ 74 Lighting Control System ........................................................ 76 ACCESS System Application Example.................................. 79 Review Answers ................................................................... 81 Final Exam ............................................................................. 82

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our sales personnel and distributors to sell Siemens Energy & Automation products more effectively. This course covers Power Monitoring and Management with ACCESS and related products. Upon completion of Power Monitoring and Management with ACCESS you should be able to:

2

•

Identify five benefits of using the ACCESS system

•

Explain the difference between peak, peak-to-peak, instantaneous, average, and effective values of AC current and voltage

•

Identify linear and nonlinear loads

•

Explain various industry terms for voltage conditions

•

Describe a CBEMA curve

•

Explain the effects of harmonics on a distribution system and associated equipment

•

Explain the difference between true power, reactive power, and apparent power

•

Identify solutions for various power supply problems

•

Select appropriate power meters for use in a distribution system

•

Explain various communication standards and network protocols

•

Explain the use of various components in an ACCESS controlled distribution system

This knowledge will help you better understand customer applications. In addition, you will be able to describe products to customers and determine important differences between products. You should complete Basics of Electricity before attempting Power Monitoring and Management with ACCESS. An understanding of many of the concepts covered in Basics of Electricity is required for Power Monitoring and Management with ACCESS. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. Sentron and Sensitrip are registered trademarks of Siemens AG. ACCESS, WinPM, SIEServe, SIPROTEC, Static Trip III, SAMMS and S7/IO are trademarks of Siemens AG. Other trademarks are the property of their respective owners.

3

Monitoring and Managing Electrical Power with ACCESS

Siemens ACCESS™ is more than just power meters, trip units, and other hardware. The ACCESS power management and control system is a networked system comprised of a variety of devices that monitor and control an electrical distribution system. The ACCESS system provides electrical data necessary for troubleshooting, power quality studies, preventative maintenance, and cost allocation. A power monitoring and management system, such as Siemens ACCESS, can identify potential problems before they cause costly breakdowns. There are five benefits to using the ACCESS system. • Reduce or eliminate unplanned outages • Proactively manage power systems to minimize utility bills • Automate sub-billing of utility power bills • Optimize capital equipment used in power systems • Measure and analyze power quality

4

Electrical Power Distribution

Before discussing the Siemens ACCESS system an understanding of the production, distribution, and use of electric power is necessary. Electric power is produced by converting potential energy into electricity. There are several sources used to produce electric power. Coal, oil, and uranium are fuels used to convert water into steam which in turn drives a turbine. Some utilities also use gas or a combination of gas and steam turbines. There are other forms of electric power generation such as hydroelectric and solar energy plants.

5

Distribution

In order for generated power to be useful it must be transmitted from the generating plant to residential, commercial, and industrial customers. Typically, commercial and industrial applications have higher demands for electric power than residential applications. Regardless of the size of the electric system, electric power must be supplied that allows the intended loads to operate properly. The most efficient way to transfer energy from the generating plant to the customer is to increase voltage while reducing current. This is necessary to minimize the energy lost in heat on the transmission lines. These losses are referred to as I2R (Isquared-R) losses since they are equal to the square of the current times the resistance of the power lines. Once the electrical energy gets near the end user the utility will need to step down the voltage to the level needed by the user.

Power Quality

6

Electrical equipment is designed to operate on power that is a specific voltage and frequency. This power should also be free from quality problems, such as voltage spikes and harmonics. Unfortunately, power quality problems can occur from various sources. Power quality problems can affect the performance and shorten the life of electrical equipment. Power quality problems can significantly increase the operating cost of an electrical system.

Loads

Electricity is used to produce motion, light, sound, and heat. AC motors, which account for about 60% of all electricity used, are widely used in residential, commercial, and industrial applications. In today’s modern commercial and industrial facilities there is increased reliance on electronics and sensitive computer-controlled systems. Electronic and computer systems are often their own worst enemy. Not only are they susceptible to power quality problems, but they are often the source of the problem.

7

Review 1 1.

Which of the following is a benefit to using the Siemens ACCESS system? a. Reduce or eliminate unplanned outages b. Proactively manage power systems c. Automate sub-billing of utility power bills d. Optimize capital equipment used in power systems e. Measure and analyze power quality f. All of the above

2.

AC motors account for about ____________ % of all electricity used.

3.

The most efficient way to transfer energy from the generating plant to the customer is to increase voltage while reducing ____________ .

4.

Power quality problems can significantly ____________ the operating cost of an electrical system. a. increase b. decrease

8

Voltage and Current Values

An accurate measurement of voltage supplied by the utility and the current produced by the connected load is necessary in identifying power usage and power quality problems. DC

Voltage is either direct current (DC) or alternating current (AC). DC voltage produces current flow in one direction. DC voltage can be obtained directly from sources such as batteries and photocells, which produce a pure DC. DC voltage can also be produced by applying AC voltage to a rectifier.

Measuring DC Voltage

The value of DC voltage varies. Low level DC voltages, such as 5 - 30 VDC, are commonly used in electronic circuits. Higher levels of DC voltage, such as 500 VDC, can be used in many industrial applications to control the speed of DC motors. A voltmeter is used to measure DC voltage.

9

AC Voltage, Current, and Frequency

Current flow in AC voltage reverses direction at regular intervals. AC voltage and current are represented by a sine wave. Sine waves are symmetrical, 360° waveforms which represent the voltage, current, and frequency produced by an AC generator. If the rotation of an AC generator were tracked through a complete revolution of 360°, it could be seen that during the first 90° of rotation voltage increases until it reaches a maximum positive value. As the generator rotated from 90° to 180°, voltage would decrease to zero. Voltage increases in the opposite direction between 180° and 270°, reaching a maximum negative value at 270°. Voltage decreases to zero between 270° and 360°. This is one complete cycle or one complete alternation. Frequency is a measurement of the number of alternations or cylces that occur in a measured amount of time. If the armature of an AC generator were rotated 3600 times per minute (RPM) we would get 60 cycles of voltage per second, or 60 hertz.

10

AC voltage can either be single- or three-phase. While singlephase power is needed for many applications, such as lighting, utility companies generate and transmit three-phase power. Three-phase power is used extensively in industrial applications to supply power to three-phase motors. In a three-phase system the generator produces three voltages. Each voltage phase rises and falls at the same frequency (60 Hz in the U.S., 50 Hz in many other countries); however, the phases are offset from each other by 120°.

Measuring AC Values

Measuring AC is more complex than DC. Depending on the situation, it may be necessary to know the peak value, peak-topeak value, instantaneous value, average value, or the RMS (root-mean-square) value of AC.

Peak Value

The peak value of a sine wave occurs twice each cycle, once at the positive maximum value and once at the negative maximum value. The peak voltage of a distribution system might be 650 volts, for example.

11

Peak-to-Peak Value

The peak-to-peak value is measured from the maximum positive value to the maximum negative value of a cycle. If the peak voltage is 650 volts, the peak-to-peak voltage is 1300 volts.

Instantaneous Value

The instantaneous value is the value at any one particular time along a sine wave. Instantaneous voltage is equal to the peak voltage times the sine of the angle of the generator armature. The sine value is obtained from trigonometric tables. The following table shows a few angles and their sine value. Angle 30° 60° 90° 120° 150° 180°

Sin θ 0.5 0.866 1 0.866 0.5 0

Angle 210° 240° 270° 300° 330° 360°

Sin θ -0.5 -0.866 -1 -0.866 -0.5 0

The instantaneous voltage at 150° of a sine wave with a peak voltage of 650 volts, for example, is 325 volts (650 x 0.5).

12

Average Value

The average value of a sine wave is zero. This is because the positive alternation is equal and opposite to the negative alternation. In some circuits it may be necessary to know the average value of one alternation. This is equal to the peak voltage times 0.637. The average value of a distribution system with 650 volts peak, for example, is 414.05 volts (650 x 0.637).

Effective Value

The effective value, also known as RMS (root-mean-square), is the common method of expressing the value of AC. The effective value of AC is defined in terms of an equivalent heating effect when compared to DC. One RMS ampere of current flowing through a resistance will produce heat at the same rate as a DC ampere. The effective value is 0.707 times the peak value. The effective value of a system with 650 volts peak, for example, is 460 volts (650 x 0.707 = 459.55 volts).

13

Linear Loads

It is important at this point to discuss the differences between a linear and nonlinear load. A linear load is any load in which voltage and current increase or decrease proportionately. Voltage and current may be out of phase in a linear load, but the waveforms are sinusoidal and proportionate. Motors, resistive heating elements, incandescent lights, and relays are examples of linear loads. Linear loads can cause a problem in a distribution system if they are oversized for the distribution system or malfunction. They do not cause harmonic distortion, which will be discussed later.

Nonlinear Loads

When instantaneous load current is not proportional to instantaneous voltage the load is considered a nonlinear load. Computers, television, PLCs, ballested lighting, and variable speed drives are examples of nonlinear loads. Nonlinear loads can cause harmonic distortion on the power supply. Harmonics will be discussed later in the course.

14

Crest Factor

Crest factor is a term used to describe the ratio of the peak value to the effective (RMS) value. A pure sinusoidal waveform has a crest factor of 1.41. A crest factor other than 1.41 indicates distortion in the AC waveform. The crest factor can be greater or lower than 1.41, depending on the distortion. High current peaks, for example, can cause the crest factor to be higher. Measuring the crest factor is useful in determining the purity of a sine wave.

Conversion Chart

When using different types of test equipment it may be necessary to convert from one AC value to another. A voltmeter, for example, may be calibrated to read the RMS value of voltage. For purpose of circuit design, the insulation of a conductor must be designed to withstand the peak value, not just the effective value. To Convert Peak-to-Peak Peak Peak Peak RMS RMS Average Average

To Peak Peak-to-Peak RMS Average Peak Average Peak RMS

Multiply By 0.5 2 0.707 0.637 1.414 0.9 1.567 1.111

15

Changes in Voltage and Current

Even the best distribution systems are subject to changes in system voltage from time-to-time. The following industry terms can be used to describe given voltage conditions. Voltage changes can range from small voltage fluctuations of short duration to a complete outage for an extended period of time. Term

Condition

Voltage Fluctuations

Increase or decrease in normal line voltage within the normal rated tolerance of the electronic equipment. Usually short in duration and do not affect equipment performance.

Voltage Sag

Decrease in voltage outside the normal rated tolerance of the electronic equipment. Can cause equipment shutdown. Generally, two seconds or less in duration.

Voltage Swell

Increase in voltage outside the normal rated tolerance of the electronic equipment. Can cause equipment failure. Generally, two seconds or less in duration.

Decrease/increase in voltage outside the normal rated Long-Term tolerance of the electronic equipment. Can adversly Under/Overvoltage affect equipment. Lasts more than a few seconds in duration. Outage/Sustained Complete loss of power. Can last from a few Power Interruption milliseconds to several hours.

16

Sags and undervoltage can be caused when high current loads, such as large motors are started. Undervoltage may also occur when a power utility reduces the voltage level to conserve energy during peak usage. Undervoltage is also commonly caused by overloaded transformers or improperly sized conductors. Swells and overvoltage can be caused when high current loads are switched off, such as when machinery shuts down. Overvoltage may occur on loads located near the beginning of a power distribution system or improperly set voltage taps on a transformer secondary.

Voltage and Current Unbalance

Voltage unbalance occurs when the phase voltages in a threephase system are not equal. One possible cause of voltage unbalance is the unequal distribution of single-phase loads. In the following illustration loads are equally divided.

17

In this illustration, however, loads are unevenly divided. A large number of lighting and small appliance loads are connected to phase C . This can cause the voltage on phase C to be lower. Because a small unbalance in voltage can cause a high current unbalance, overheating can occur in the C phase winding of the 3-phase motor. In addition, the single-phase motors connected to phase C are operating on a reduced voltage. These loads will also experience heat related problems.

Transient Voltage

18

A transient voltage is a temporary, undesirable voltage that appears on the power supply line. Transient voltages can range from a few volts to several thousand volts and last from a few microseconds to a few milliseconds. Transients can be caused by turning off high inductive loads, switching large power factor correction capacitors, and lightning strikes.

CBEMA and IEEE

The U.S. Department of Commerce, working with the Computer Business Equipment Manufacturers Association (CBEMA), published a set of guidelines for powering and protecting sensitive equipment. These guidelines were published in 1983 in FIPS Publication 94. As the use of computers has grown, other organizations have made additional recommendations. The Institute of Electrical and Electronic Engineers (IEEE) published IEEE 446-1987 which recommends engineering guidelines for the selection and application of emergency and standby power systems. While it is beyond the scope of this book to discuss in detail the recommendations of these documents it is useful to discuss their intent.

CBEMA Curve

The CBEMA curve is a useful tool that can be used as a guideline in designing power supplies for use with sensitive electronic equipment. The vertical axis of the graph is the percent of rated voltage applied to a circuit. The horizontal axis is the time the voltage is applied. The CBEMA curve illustrates an acceptable voltage tolerance envelope. In general, the greater the voltage spike or transient, the shorter the duration it can occur. Voltage breakdown and energy flow problems can occur when the voltage is outside the envelope.

19

Power Disturbance Types

There are three types of power disturbances. Type I disturbances are transient and oscillatory overvoltages lasting up to 0.5 Hz. Type I disturbances can be caused by lightning or switching of large loads on the power distribution system. Type II disturbances are overvoltages and undervoltages which last from 0.5 to 120 Hz. Type II disturbances can be caused by a fault on the power distribution system, large load changes, or malfunctions at the utility. Type III disturbances are outages lasting greater than 120 hertz. Studies have shown that sensitive computer equipment is most vulnerable during a Type I overvoltage disturbance and a Type II undervoltage disturbance. Type II undervoltage disturbances are the most common cause of failure in sensitive computer equipment. It is important to note that the precise extent to which computers and other sensitive equipment is susceptible is difficult to determine.

20

Review 2 1.

____________ is a measurement of the number of alternations between positive and negative peak values in a measured amount of time. a. voltage b. current c. frequency d. power

2)

The peak-to-peak value of an AC voltage with a peak voltage of 600 volts is ____________ .

3)

The instantaneous voltage measured at 120° of a sine wave with a peak voltage of 650 volts is ___________ .

4)

The most common method of expressing the value of AC voltage and current is ____________ value. a. average b. effective c. peak d. instantaneous

5)

A pure sinusoidal waveform has a crest factor of ____________ .

6)

Computer equipment is most vulnerable during a Type I overvoltage disturbance and a Type ____________ undervoltage disturbance. a. I b. II c. III

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Frequency and Harmonics

We learned earlier that frequency is a measurement of the number of times voltage and current rises and falls to alternating peak values per second. Frequency is stated in hertz. The standard power line frequency in the United States is 60 hertz (60 cycles per second). In many other parts of the world the standard frequency is 50 hertz.

Harmonics

Harmonics are created by electronic circuits, such as, adjustable speed drives, rectifiers, personal computers, and printers. Harmonics can cause problems to connected loads. The base frequency of the power supply is said to be the fundamental frequency or first harmonic. The fundamental frequency or first harmonic of a 60 Hz power supply is 60 Hz. Additional harmonics can appear on the power supply. These harmonics are usually whole number multiplies of the first harmonic. The third harmonic of a 60 Hz power supply, for example, is 180 Hz (60 x 3).

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When a harmonic waveform is superimposed on the fundamental sine wave a distinctive waveform is produced. In this example, the third harmonic is seen superimposed on the fundamental frequency. The problem of waveform distortion becomes more complex when additional harmonics are present.

Total Harmonic Distortion

Harmonic distortion is a destructive force in power distribution systems. It creates safety problems, shortens the life span of transformers, and interferes with the operation of electronic devices. Total harmonic distortion (THD) is a ratio of harmonic distortion to the fundamental frequency. The greater the THD the more distortion there is of the 60 Hz sine wave. Harmonic distortion occurs in voltage and current waveforms. Typically, voltage THD should not exceed 5% and current THD should not exceed 20%. Some of the power meters offered by Siemens are capable of reading THD.

Phasors

Phase rotation describes the order in which waveforms from each phase cross zero. Waveforms can be used to illustrate this relationship. Phasors consist of lines and arrows and are often used in place of waveforms for simplification.

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Harmonic Sequence

A harmonic’s phase rotation relationship to the fundamental frequency is known as harmonic sequence. Positive sequence harmonics (4th, 7th, 10th, ...) have the same phase rotation as the fundamental frequency (1st). The phase rotation of negative sequence harmonics (2nd, 5th, 8th, ...) is opposite the fundamental harmonic. Zero sequence harmonics (3rd, 6th, 9th, ...) do not produce a rotating field. Harmonic 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th

Frequency 60 120 180 240 300 360 420 480 540 600

Sequence Fundamental Negative Zero Positive Negative Zero Positive Negative Zero Positive

Odd numbered harmonics are more likely to be present than even numbered harmonics. Higher numbered harmonics have smaller amplitudes, reducing their affect on the power and distribution system.

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Harmonic Effects

All harmonics cause additional heat in conductors and other distribution system components. Negative sequence harmonics can be problematic in induction motors. The reverse phase rotation of negative harmonics reduces forward motor torque and increases the current demand.

Zero sequence harmonics add together, creating a single-phase signal that does not produce a rotating magnetic field. Zero sequence harmonics can cause additional heating in the neutral conductor of a 3Ø, 4-wire system. This can be a major problem because the neutral conductor typically is not protected by a fuse or circuit breaker.

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K Factor

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K factor is a simple numerical rating that indicates the extra heating caused by harmonics. A transformer’s ability to handle the extra heating is determined by a K factor rating. A standard transformer has a rating of K-1. A transformer might have a rating of K-5, which would be an indication of the transformer’s ability to handle 5 times the heating effects caused by harmonics than a K-1 rated transformer.

Power and Power Factor

Load Types

Distribution systems are typically made up of a combination of various resistive, inductive, and capacitive loads.

Resistive Loads

Resistive loads include devices such as heating elements and incandescent lighting. In a purely resistive circuit, current and voltage rise and fall at the same time. They are said to be “in phase.”

True Power

All the power drawn by a resistive circuit is converted to useful work. This is also known as true power in a resistive circuit. True power is measured in watts (W), kilowatts (kW), or megawatts (MW). In a DC circuit or in a purely resistive AC circuit, true power can easily be determined by measuring voltage and current. True power in a resistive circuit is equal to system voltage (E) times current (I). In the following example, an incandescent light (resistive load) is connected to 120 VAC. The current meter shows the light is drawing 0.833 amps. In this circuit 100 watts of work is done (120 VAC x 0.833 amps).

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Inductive Loads

Inductive loads include motors, transformers, and solenoids. In a purely inductive circuit, current lags behind voltage by 90°. Current and voltage are said to be “out of phase.” Inductive circuits, however, have some amount of resistance. Depending on the amount of resistance and inductance, AC current will lag somewhere between a purely resistive circuit (0°) and a purely inductive circuit (90°). In a circuit where resistance and inductance are equal values, for example, current lags voltage by 45°.

Capacitive Loads

Capacitive loads include power factor correction capacitors and filtering capacitors. In a purely capacitive circuit, current leads voltage by 90°. Capacitive circuits, however, have some amount of resistance. Depending on the amount of resistance and capacitance, AC current will lead voltage somewhere between a purely resistive circuit (0°) and a purely capacitive circuit (90°). In a circuit where resistance and capacitance are equal values, for example, current leads voltage by 45°.

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Reactive Loads

Circuits with inductive or capacitive components are said to be reactive. Most distribution systems have various resistive and reactive circuits. The amount of resistance and reactance varies, depending on the connected loads.

Reactance

Just as resistance is opposition to current flow in a resistive circuit, reactance is opposition to current flow in a reactive circuit. It should be noted, however, that where frequency has no effect on resistance, it does effect reactance. An increase in applied frequency will cause a corresponding increase in inductive reactance and a decrease in capacitive reactance.

Energy in Reactive Circuits

Energy in a reactive circuit does not produce work. This energy is used to charge a capacitor or produce a magnetic field around the coil of an inductor. Current in an AC circuit rises to peak values (positive and negative) and diminishes to zero many times a second. During the time current is rising to a peak value, energy is stored in an inductor in the form of a magnetic field or as an electrical charge in the plates of a capacitor. This energy is returned to the system when the magnetic field collapses or when the capacitor is discharged.

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Reactive Power

Power in an AC circuit is made up of three parts; true power, reactive power, and apparent power. We have already discussed true power. Reactive power is measured in volt-amps reactive (VAR). Reactive power represents the energy alternately stored and returned to the system by capacitors and/or inductors. Although reactive power does not produce useful work, it still needs to be generated and distributed to provide sufficient true power to enable electrical processes to run.

Apparent Power

Not all power in an AC circuit is reactive. We know that reactive power does not produce work; however, when a motor rotates work is produced. Inductive loads, such as motors, have some amount of resistance. Apparent power represents a load which includes reactive power (inductance) and true power (resistance). Apparent power is the vector sum of true power, which represents a purely resistive load, and reactive power, which represents a purely reactive load. A vector diagram can be used to show this relationship. The unit of measurement for apparent power is volt amps (VA). Larger values can be stated in kilovolt amps (kVA) or megavolt amps (MVA).

Power Factor

Power factor (PF) is the ratio of true power (PT) to apparent power (PA), or a measurement of how much power is consumed and how much power is returned to the source. Power factor is equal to the cosine of the angle theta in the above diagram. Power factor can be calculated with the following formulas.

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Power factor can be given as a percent or in decimal format. The following table shows the power factor for a few sample angles. Angle Theta 0 10 20 30 45 60 70 80 90

Cosine of Angle Theta 1 0.98 0.94 0.87 0.70 0.50 0.34 0.17 0

Power Factor (%) 100% 98% 94% 87% 70% 50% 34% 17% 0%

Power Factor (Decimal) 1 .98 .94 .87 .7 .5 .34 .17 0

In purely resistive circuits, apparent power and true power are equal. All the power supplied to a circuit is consumed or dissipated in heat. The angle of theta is 0° and the power factor is equal to 1. This is also referred to as unity power factor. In purely reactive circuits, apparent power and reactive power are equal. All power supplied to a circuit is returned to the system. The angle theta is 90° and the power factor is 0. In reality, all AC circuits contain some amount of resistance and reactance. In a circuit where reactive power and true power are equal, for example, the angle of theta is 45° and power factor is 0.70.

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Power Factor Problems

It can be seen that an increase in reactive power causes a corresponding decrease in power factor. This means the power distribution system is operating less efficiently because not all current is performing work. For example, a 50 kW load with a power factor of 1 (reactive power = 0) could be supplied by a transformer rated for 50 kVA. However, if power factor is 0.7 (70%) the transformer must also supply additional power for the reactive load. In this example a larger transformer capable of supplying 71.43 kVA (50 ÷ 70%) would be required. In addition, the size of the conductors would have to be increased, adding significant equipment cost.

The Cost of Power

Utility companies sell electrical power based on the amount of true power measured in watts (W). However, we have learned that in AC circuits not all power used is true power. The utility company must also supply apparent power measured in voltamps (VA). Typically utilities charge additional fees for increased apparent power due to poor power factor.

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The following table shows the amount of apparent power (VA = W ÷ PF) required for a manufacturing facility using 1 MW (megawatt) of power per hour for a few sample power factors. If, for example, a manufacturing facility had a power factor of 0.70 the utility company would have to supply 1.43 MVA (mega voltamps) of power. If the power factor were corrected to 0.90 the power company would only have to supply 1.11 MVA of power. T ru e P o w er (M W ) T ru e P o w er

1

Leading and Lagging Power Factor

P o w er Fac to r ÷ P o w er Fac to r 1 0.95 0.90 0.85 0.80 0.75 0.70

Apparen t P o w er (M VA) = A pparen t P o w er 1 1.053 1.11 1.18 1.25 1.33 1.43

Since current leads voltage in a capacitive circuit, power factor is considered leading if there is more capacitive reactance than inductive reactance. Power factor is considered lagging if there is more inductive reactance than capacitive reactance since current lags voltage in a inductive circuit. Power factor is unity when there is no reactive power or when inductive reactance and capacitive reactance are equal, effectively cancelling each other. It is usually more economical to correct poor power factor than to pay large utility bills. In most industrial applications motors account for approximately 60% or more of electric power consumption, resulting in a lagging power factor (more inductive than capacitive). Power factor correction capacitors can be added to improve the power factor.

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Power Demand

Demand is the average energy consumed over a specified period of time. The interval is usually determined by the utility company and is typically 15 or 30 minutes. The utility measures the maximum demand over the 15 or 30 minute period. Utility companies must install larger equipment to handle irregular demand requirements. For this reason utility companies may charge large customers an additional fee for irregular power usage during peak times. If the maximum demand is greater than the average consumption, the utility company will need to provide increased generating capacity to satisfy the higher demand. Demand is usually low in the morning and evening. During the day there is more demand for electrical power. Siemens power meters have a sliding window adjustment that allows the user to monitor time segments specified by the utility company.

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Solutions

As we have learned, there are a number of things that can affect power quality. The following table provides some basic guidelines to solve these problems. It should be remembered that the primary cause and resulting effects on the load and system should be considered when considering solutions. Problem Sag

Swell

Undervoltage

Overvoltage

Momentary Power Interruption

Noise

Transients

Harmonics

Power Factor

Effect Computer shutdown resulting in lost data, lamp flicker, electronic clock reset, false alam. Shorten equipment life and increase failure due to heat. Computer shutdown resulting in lost data, lamp flicker, electronic clock reset, false alam. Life expectency of motor and other insulation resulting in equipment failure or fire hazard. Shorten life of light bulbs Computer shutdown resulting in lost data, lamp flicker, electronic clock reset, false alam, motor circuits trip. Erractic behavior of electronic equipment, incorrect data communication between computer equipment and field devices. Premature equipment failure, computer shutdown resulting in lost data. Overheated neutrals, wires, connectors, transformers, equipment. Data communication errors. Increased equipment and power costs

Solution Voltage regulator, power line conditioner, proper wiring. Voltage regulator, power line conditioner. Voltage regulator, power line conditioner, proper wiring. Voltage regulator, power line conditioner.

Voltage regulator, power line conditioner, UPS system.

Line filters and conditioners, proper wiring and grounding.

Surge suppressor, line conditioner, isolation transformers, proper wiring, grounding. Harmonic filters, K-rated transformers, proper wiring and grounding.

Power factor correction capacitors.

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Review 3 1.

The second harmonic of a 60 Hz power supply is ____________ Hz.

2.

Typically, the total harmonic distortion (THD) of a voltage waveform should not exceed ____________ %.

3.

____________ sequence harmonics do not produce a rotating magnetic field. a. Positive b. Negative c. Zero

4.

A transformer’s ability to handle the extra heating caused by harmonics is determined by a ____________ rating.

5.

In a purely ____________ circuit, voltage and current are in phase. a. resistive b. inductive c. capacitive

6.

____________ power represents a load which includes reactive power and true power.

7.

____________ is the ratio of true power to apparent power.

8.

An increase in reactive power would require a corresponding ____________ in transformer size. a. increase b. decrease

9.

It is possible to correct for sag with the addition of a ____________ . a. voltage regulator b. power line conditioner c. proper wiring d. all of the above

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ACCESS System

Up to this point we have looked at how various factors effect power quality. The following sections will focus on components of the ACCESS system and how they can be used as a complete power monitoring and management system. Supervisory Devices

In general, ACCESS works on two levels: supervisory and field. Supervisory devices, such as WinPM™, collects and displays information from a network of field devices. A supervisory device sends requests and receives feedback from field devices over a serial network. This process, called polling, allows the supervisory and field devices to exchange information. Siemens WinPM software runs on a personal computer (PC).

Field Devices

Field devices include meters, circuit breakers, protective relays, I/O devices, motor protectors, and personal computers (PCs). Field devices send and receive information about an electrical system. In the following sections we will look at ACCESS system products used as supervisory devices, in network communication, and field devices.

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WinPM and SIEServe

WinPM

WinPM™ is supervisory software designed for monitoring and control of any facility’s electrical distribution system. WinPM can run on a single computer or in a networked environment. Multiple computers running WinPM can share data and control devices over a LAN using TCP/IP. WinPM can monitor an entire electrical system consisting of hundreds of field devices in multiple locations.

Electrical System Management

WinPM monitors and collects data of an electrical system by interfacing to any communicating electrical device such as power meters, relays, and trip units. Alarms can be setup to trigger if a specific value, such as voltage, current, or KW demand, is exceeded. Alarms can alert via audible and visual messages on a PC, fax, or pager message, and/or automatically control a connected device.

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Analysis

Power quality, such as transients, sags, swells, and harmonics, can be monitored and analyzed by viewing triggered waveforms, continuous data sampling, relay trip logs, and setpoint event messages. Historical data logs can be generated to provide load profile information, kilowatt demand usage patterns, harmonic, and power factor trends. These historical data logs can provide trending on any measured value.

Device Configuration

ACCESS field devices can be configured remotely by specifying protective settings. Certain field devices can be configured to record waveforms.

Device Control

Certain devices can be controlled directly from WinPM. For example, motors can be started and stopped using Siemens Advanced Motor Master System (SAMMS) devices.

SIEServe

SIEServe™ is another electrical distribution software product designed by Siemens. SIEServe allows for the retrieval and display of data from Siemens power meters, trip units, and relays. SIEServe, though not as robust as WinPM, provides a simple way to monitor an electrical distribution system from a desktop. Data retrieved by SIEServe can be linked to spreadsheets for charting or word processing programs for other reporting functions. SIEServe does not have the control capabilities of WinPM.

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Industrial Computer

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Siemens software, such as WinPM and SIEServe, will run on most personal computers. In some applications it may be desirable to locate a supervisory computer in a harsh industrial environment. The Siemens industrial personal computer was designed for this purpose. The Siemens industrial computer is dust proof and drip proof to NEMA 4, NEMA 4X, and NEMA 12 specifications. There is a 10.4” flat screen monitor and full keypad with an integrated pointing device. This computer is designed for panel mounting.

Communication Protocols and Standards

The ACCESS system allows a variety of devices to communicate electronically. In the following illustration, for example, several power meters are connected to a single computer.

Straight-Line Topology

Field devices can be connected to supervisory devices with either straight-line or loop topology. In straight-line topology the supervisory device connects to a field device, which in turn connects to another field device, terminating at the farthest device. Straight-line topology allows for longer runs; however, if a break in the line should occur the supervisory device would be unable to communicate with devices on the far side of the break.

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Loop Topology

In loop topology the cable is connected in a similar manner to straight-line topology. Rather than terminating the connection at the farthest device, a complete loop is formed by bringing the cable back to the supervisory device. Loop topology requires more cable than straight-line topology, which adds expense to the system and shortens the distance from the last device on the loop to the supervisory device. The main advantage to loop topology is the ability to continue to communicate with each device if there is a break in the system.

Protocols

Network protocols are rules that allow devices to communicate with each other. A protocol identifies how devices should identify each other, the form communicated data takes, and how the data is interpreted at its final destination. Several protocol standards have evolved in the electrical industry. Siemens ACCESS supports the following protocols at various levels.

PROFIBUS DP

PROFIBUS DP is an open bus standard for a wide range of applications in various manufacturing and automation applications. PROFIBUS DP works at the field device level such as, power meters, I/O devices, motor protectors, circuit breakers, and lighting controls. An advantage to PROFIBUS DP is the ability to communicate between devices of different manufacturers.

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ModBus RTU

ModBus RTU is a protocol originally developed by MODICON, which is now part of Schneider Automation. ModBus RTU protocol has been widely used by other companies.

DNP 3.0

Distributed Network Protocol 3.0 (DNP 3.0) was developed by Harris Distributed Automation Products. This protocol is an open and public protocol based on standards developed by the International Electrotechnical Commission (IEC). This protocol is often used by large power utility companies.

SEABus and SEABus Plus

The rules that govern the communication of the ACCESS system are known collectively as SEABus and SEABus Plus. Both protocols are used to communicate between supervisory and field devices. SEABus and SEABus Plus are open protocols available to anyone who wants to connect their equipment to the ACCESS system. A supervisory device can support unlimited field devices. Each field device in the ACCESS system has a unique address. A packet is simply a unit of data that is routed between an origin (supervisory device) and a destination (field device). Data bytes are grouped into packets containing from 5 to 260 characters. Data bytes contain a unique address for a given field device and instructions for the field device. A supervisory device, for example, may initiate communication by sending a packet requesting information such as voltage from a specific field device. The field device would respond by sending a packet back with the requested information.

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Local Area Networks

Local Area Network (LAN)

In any complex power monitoring system the need for rapid information flow is critical. Conditions at any point in the system may impact the entire power distribution system. This need for information flow often requires that intelligent devices, such as supervisory PCs, be interconnected by a local area network (LAN). A LAN is a communication system designed for private use in a limited area. A node is an active device, such as a computer or printer, connected to the network. A LAN can be arranged with nodes in a bus, star, or a combination of bus and star. One example of a widely used LAN is Ethernet. Ethernet uses a bus topology and an access control system that allows devices to initiate communication only if a carrier signal is not present. By comparison, Token Ring networks use a ring topology and a signal called a token to determine which device can communicate.

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Ethernet Converter

The Siemens Ethernet converter connects many ACCESS field devices throughout a facility to a supervisory computer. The Ethernet converter can be configured so that Siemens ACCESS components can communicate through the Ethernet or Token Ring.

The Ethernet converter can connect RS-232 and RS-485 devices directly to a LAN.

The converter is also capable of connecting up to two protocols, such as SEABus and ModBus RTU.

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Serial Communication

RS-232 and RS-485 are Electronic Industries Association (EIA) specifications commonly used for serial data communication. Siemens ACCESS devices support the RS-485 as standard. Some ACCESS devices also support the RS-232 standard. RS-232

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RS-232 is a serial communication protocol which sends and receives information through twisted pair cable. It is common to see both 9-pin and 25-pin RS-232 connectors. It is important to note that although the RS-232 standard consists of 25 transmission lines, many applications do not require all the lines available. Depending on the device, manufacturers use various combinations of the transmission lines available. The following illustration, for example, shows the connector requirements for equipment used in the Siemens ACCESS system.

RS-232 uses what is referred to as an unbalanced signal or communication method. There is one signal wire for each circuit with a common return. The driver sends a series of binary signals to the receiver. These binary pulses make up predefined words that either give the status of a system being monitored or provide commands to control an event. This method is susceptible to unwanted electrical noise. The RS-232 standard supports only one driver (transmitter) and one receiver with distances limited to no greater than 50 feet.

RS-485

RS-485 is a communication standard that is better suited for industrial applications that involve distances greater than 50 feet. The RS-485 standard can support up to 32 devices over a maximum distance of 4000 feet.

The RS-485 standard uses a twisted pair of wires for each circuit with differential drivers and receivers. This method provides a balanced signal which cancels out signal noise to allow for better data integrity.

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Typically, at the top level of a communication system is a host computer with an RS-232 interface. The host computer may have to communicate with an RS-485 device. In this situation a converter, such as a Siemens isolated multi-drop converter can be used.

Isolated Multi-Drop Converter

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The Isolated Multi-Drop Converter is an RS-232 to RS-485 converter that provides connectivity between a computer’s RS232 serial port and a Siemens SEABus RS-485 communications loop for ACCESS field devices. A multi-drop converter will accept up to four RS-485 input loops. Each input loop will support up to 32 devices. One isolated multi-drop converter can handle up to 128 field devices.

Using the Isolated Muli-Drop Converter

In the following illustration a computer communicates with various ACCESS field devices through an RS-232 interface and isolated multi-drop converter.

Communicating on a LAN

Field devices in the Siemens ACCESS product line that cannot communicate directly on a LAN, such as Ethernet, can be connected to the LAN through an Ethernet converter. When more than 32 field devices are used an isolated multi-drop converter is also required.

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Modem

Modems are electronic devices used for sending and receiving data over long distances. The Siemens ACCESS system also supports data communication through a modem. In the following illustration a remote computer communicates to an isolated multi-drop converter through a modem.

Fiber Optics

Fiber optics is a method for transmitting data using light. A basic system consists of a transmitting device which generates a light signal, a fiber optic cable, and a receiving device. In the following illustration a supervisory computer is connected to a fiber optic converter through an RS-232 interface. At the other end of the fiber optic cable is another RS-232 to fiber optic converter which is connected to an isolated multi-drop converter. The RS-485 output of the multi-drop converter is connected to various field devices.

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DTU3005

The DTU3005 is a multiple-function data transfer unit, which acts as an intelligent device to request information from up to 32 ACCESS devices. The requested information is then made available to PLCs and various industrial automation networks such as ModBus and PROFIBUS DP. There are two models, the DTU3005-P and DTU3005-B.

The following illustration shows two possible configurations. Up to 32 Siemens ACCESS devices can be connected to one port of the DTU3005. In one example, a PLC or ModBus master device can be connected to one port of a DTU3005-B. A second ModBus device or an optional supervisory PLC can be connected with SEABus to another port. In the second example, PROFIBUS devices are connected via an RS-485 port on the DTU3005-P. A supervisory PC is connected to an available port.

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Local Display Unit

The Local Display Unit (LDU) works with the SEABus network to poll data from Siemens ACCESS compatible devices. The LDU can be mounted in harsh industrial environments and is suitable for mounting in panelboards, switchboards, and switchgear.

The LDU can be connected through SEABus to up to 32 ACCESS devices. A second port can be connected through RS-232 to a WinPM monitoring station.

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Review 4 1.

WinPM is an example of a ____________ device. a. supervisory b. field

2.

A Siemens ACCESS power meter is an example of a ____________ device. a. supervisory b. field

3.

The rules that govern the communication fo the ACCESS system are known collectively as ____________ and ____________ Plus.

4.

A ____________ is an active device, such as a computer or printer, connected to the network.

5.

Siemens ____________ ____________ can connect RS-232 and RS-485 devices directly to a LAN.

6.

RS-232 is limited to transmission distances no greater than ____________ feet.

7.

RS-485 can support 32 different drivers and receivers over a maximum distance of ____________ feet.

8.

The LDU can be connected to up to ____________ ACCESS devices.

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Power Metering

In today’s electronic environment, power management requires sophisticated meters. Voltage, current, and kW meters alone do not provide an adequate indication of power quality and energy consumption. Siemens power meters, in addition to measuring voltage, current, frequency, harmonics energy, power, and power factor, also capture system disturbances, log historical data, monitor the status of other equipment, and control loads.

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Meter Location

Power meters should be located at key points in the electrical distribution system to effectively monitor power consumption and quality. In some applications, it is sufficient to monitor energy consumption on significant loads and monitor power quality at the utility supply point. In critical power applications it may be desirable to monitor power quality throughout the distribution system.

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9230 Meter

The 9230 power meter measures real power. It will provide a readout of watts, watt-hours, and watt demand (configurable demand period). The 9230 is a full four-quadrant power meter providing bidirectional monitoring and separate positive and negative watt-hour accumulators.

The 9230 meter measures voltage and current to calculate power. Alarm functions can be programmed to operate two relay contacts. A KYZ relay provides pulses for energy management systems. These pulses represent accumulated positive or negative watt-hours. The pulse value is configurable. SEABus communication converters or analog output modules are available.

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4300 Meter

The 4300 meter provides a readout of phase current, average phase current, line voltage, average line voltage, frequency, watts, watt-hours, peak watt demand, and power factor. Like the 9230, the 4300 is a full four-quadrant power meter. A standard communications module connects the 4300 to the Siemens ACCESS system. A separate display eliminates the need for voltage transformers on most low voltage applications because line voltage can be connected directly to the base module.

The 4300 meter is designed to fit in new or retrofit applications. The display unit will fit standard U.S. analog meter drilling patterns.

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9240 Meter

The 9240 meter provides all significant parameters of the power system including; 3-phase volts, 3-phase current, neutral current, watts, VAR, VA, watt-hours, power factor, and frequency. The 9240 records the maximum and minimum values for most measured parameters. Three KYZ pulses are available for energy readings. The 9240 uses standard cutouts and will replace most existing analog meters. The 9240 has several protocol options to support many systems. Available protocols include SEABus (for the ACCESS system), ModBus RTU, ModBus Plus, and DNP 3.0.

9300 Meter

The 9300 meter also provides all significant parameters of the power system. The 9300 meter can make predicted demand calculations based on past data. The 9300 meter monitors individual phase harmonics (up to the 15th), total harmonic distortion, and K-factor. The 9300 includes four binary outputs that can be operated from remote software or configured as kWH pulse signals. The 9300 comes standard with SEABus (for the ACCESS System) and ModBus RTU or, optionally, with PROFIBUS DP. An Ethernet card may also be installed.

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The 9300 includes a front optical data port for accessibility by a portable PC.

9330 Meter

The 9330 meter offers the same features as the 9300 meter. In addition, the 9330 includes setpoint capability to operate any of the four binary outputs. All events are recorded in the event log. The 9330 can also sample data continuously for future trend analysis. The 9330 meter features Ethernet or telephone modem connections as options. The 9330 can act as a gateway between these connections and other devices that are connected to the 9330 with an RS-485 cable. The 9330 comes standard with SEABus, ModBus RTU, and DNP 3.0.

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4700 Meter

In addition to providing information on all significant parameters of a power system, the 4700 includes waveform capture for harmonic analysis up to the 63rd harmonic. The 4700 includes 4 binary inputs and 1 analog input to monitor external equipment. There are 3 relay outputs that can be operated by set-points or used as kWh and kVARH pulse signals. The 4700 meter also includes one transducer-type analog output.

4720 Meter

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The 4720 meter provides all of the same features as the 4700 meter. In addition, the 4720 provides on-board harmonic analysis up to the 15th harmonic. Like the 9330, the 4720 logs events and does continuous data sampling. The 4720 provides a 2-cycle trigger to record up to 36 cycles of a disturbance. The 4720 has an optional communications card for SEABus protocol.

9500 Meter

The 9500 offers three-phase power monitoring on a large, easy to read screen. The 9500 meter monitors K-factor, crest factor, individual harmonics, and total harmonics up to the 63rd harmonic. In addition to displaying values, the 9500 also displays graphical phasor diagrams and bar graph representations. The 9500 provides a 0.5 cycle trigger and up to 4 MB of memory for extensive waveform recording of system disturbances, as well as a special sag/swell module. Advanced features include utility-style rate structure calculations. The 9500 meter meets the accuracy requirements of the ANSI C12.20 revenue standard. The 9500 provides transformer and line loss calculations. The 9500 can communicate with the Internet and transmit email. The 9500 comes standard with several protocols including SEABus, ModBus RTU, and DNP 3.0. In addition to RS-232 and RS-485, the 9500 can include a telephone modem, an Ethernet card, and a fiber optic port. Simultaneous connections are supported. The 9500 can be equipped with 7 binary outputs, 16 binary inputs, 4 analog outputs, and 4 analog inputs.

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Another unique feature of the 9500 is the optional ability to connect to the Global Position Satellite (GPS) system for time synchronization with other 9500 meters in the distribution system.

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Power Meter Features

Siemens power meters have various features, depending on specific application needs. With a number of meters to choose from it may seem confusing when trying to decide which meter is right for which job. The following chart and tables are provided to help identify various features and performance capabilities for Siemens power meters. The chart is arranged in order of performance feature. The table on the following page details available features for each power meter.

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Data Logging

Display I/O

Advanced Functions

Communications

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Real Power Bi-Directional Energy Sliding Window Demand Reactive & Apparent Power Voltage & Current Power Factor Frequency Harmonic Analysis Thermal & Predicted Demand Power Harmonics Symmetrical Components Min/Max Data Sampling Event Logging Waveform Recording Easy to read Alpha-numeric Display High resolution graphical Display Relays/Pulse Outputs Counter/Status Inputs Analog Outputs Analog Inputs Set-point Control Phase Reversal / Unbalance TOU & Line Loss Compensation Math & Logic GPS Time Synch Sag/Swell Detection Transient Detection SEABus Modbus RTU DNP 3.0 Profibus DP RS232 / RS485 Ethernet Modem Fiber Optic

9500

4720

4700

9330

9300

9240

4300

9230 Measurements

Review 5 1.

Power meters should be located at ____________ points in the electrical distribution system.

2.

The ____________ and ____________ meters include a front optical data port for accessibility by a portable PC.

3.

The 4720 meter provides on-board harmonic analysis up to the ____________ harmonic.

4.

A unique feature of the 9500 meter is the optional ability to connect to ____________ for time synchronization with other 9500 meters in the distribution system.

5.

The ____________ meter has a high resolution graphical display.

65

Protective Relays and Trip Units

The term switchgear is used to describe coordinated devices used for control and protection of equipment such as generators, transformers, capacitor banks, motors, and distribution lines. SIPROTEC 7SJ61, 62, and 63 are microprocessor-based protective relays designed to provide protective relay functions, metering, and control associated with switchgear circuit breaker installations.

66

SIPROTEC

SIPROTEC is a trade name used by Siemens to identify a group of Siemens multifunction protection relays, such as the 7SJ61, 7SJ62, and 7SJ63. Multifunction protection relays provide the basic protection required in power systems, such as phase and ground overcurrent protection on feeder circuits, motors, and transformers. However, since they are microprocessor based, they can also communicate what is happening to the equipment they are protecting. Examples of information they can communicate to the ACCESS power monitoring system include: protective element status, trip diagnostics, and integrated metering of the power at its input. SIPROTEC relay features are integrated into the ACCESS single-line animation, waveform support, and alarm handling. SIPROTEC relays have integrated PLC logic and support multiple protocols. DIGSI is a software package available for SIPROTEC which supports documentation, archiving of relay data, and advanced diagnostics.

67

Circuit Breaker Trip Units

The following sections describe low voltage insulated case (ICCB), molded case (MCCB) circuit breakers, and Type RL circuit breakers with Static Trip III™ available for use with the ACCESS system. ICCB

68

Siemens Sentron® ICCB circuit breakers are available in ratings from 800 to 5000 amps and are designed to supply high short time withstand and high interrupting ratings. Two types of interchangeable trip units are available for use with the ICCB and ACCESS system; the basic type TL trip unit and the high performance System Breaker Energy Communicating trip unit (SB-EC). Both trip units use a microprocessor to execute the numerous functions programmed in the unit.

The TL trip unit features a full range of industry standard protective settings. The high-performance Systems Breaker Energy Communicating trip unit (SB-EC Trip Unit) offers advanced metering, protective relaying, time-stamped logs, and power quality monitoring functions. An LCD graphical display provides real-time voltage and current waveforms.

MCCB

Siemens Sentron MCCB circuit breakers are available in a digital version, referred to as Sensitrip® III. Sensitrip III circuit breakers utilize a microcomputer which makes it possible to customize overcurrent protection to match the loads of an electrical system. In addition, the Sensitrip III trip unit has communications capability when provided with an expansion plug and connected to a Multiplexer Translator. Sensitrip III can measure and communicate RMS phase current, pickup status, and communications status.

69


Siemens RL series low voltage power circuit breakers are used in Siemens low voltage switchgear. RL series circuit breakers are designed for up to 600 volt service with current capacities up to 5000 amps. The RL circuit breaker in the following illustration is shown with a Static Trip III™ trip unit.

Static Trip III

Static Trip III™ units are microprocessor controlled, overcurrent protective devices for use on Type RL low-voltage power circuit breakers. An optional Breaker Display Unit (BDU) can be added to communicating trip units. The BDU displays real-time measurements, trip log, event log, and min/max values.

70

The Static Trip III consists of four models:

III IIIC IIICP IIICPX

Static Trip Family Basic Overcurrent Protection Added Communications and Current Metering Added Power Metering Extended Protective Relaying

A standard feature of the Static Trip IIIC, IIICP, and IIICPX trip units is an alarm output. Any measured parameter can be set to activate the alarm based on threshold and time delay set points. These units also include several logging functions for recording trip events, pickup conditions, alarm activity, and min/max measured values. Static Trip IIIC, IIICP, and IIICPX trip units have added communication ability. Metered parameters can be displayed and configured locally on the BDU or remotely via the RS-485 communications port through the ACCESS system. Measured Value

STIIIC

STIIICP/CPX Accuracy

Phase Current

1.00%

Average Current

1.00%

Ground Current

1.00%

Phase Line-to-Neutral Voltage

1.00%

Average Line-to-Neutral Voltage

1.00%

Line-to-Line Voltage for all Phases

1.00%

Average Line-to-Line Voltage

2.00%

kW Total for all Phases

2.00%

kWh Total for all Phases

2.00%

kW Reverse

2.00%

kW Demand

2.00%

kVA

2.00%

kVAR

2.00%

kVARh Total for all Phases

2.00%

Power Factor

4.00%

Frequency

0.25%

71

SAMMS

The Siemens Advanced Motor Master System (SAMMS™) is a microprocessor-based motor control and protection device. SAMMS LV units provides all motor starting functions and thermal protection. SAMMS is a compact system with programmable control logic that replaces timers, control relays, push-buttons, selector switches, pilot devices, and associated wiring. Some of the more powerful features of the SAMMS unit include: motor run time hours, number of motor starts, number of motor trips, set point alarms, and ground fault protection.

72

ACCESS Communication

SAMMS connects to SEABus through an optional SAMMS Communication Module (CM-1). The CM-1 provides an RS-485 interface to communicate with the ACCESS system.

73

S7 I/O Device

The S7 I/O™ device is an addressable modular input/output (I/O) device that links power system components to the ACCESS system. This device is a programmable logic controller (PLC), customized to communicate using SEABus.

PLCs consist of input modules or points, a central processing unit (CPU), and output modules or points. An input to a PLC may come from a variety of digital or analog signals from various field devices. The PLC converts the input signal into a logic signal that can be used by the CPU. Output modules convert control signals from the CPU into a digital or analog signal that can be used to control various field devices.

74

The S7-I/O device provides the capability to monitor and control power system elements that are not specifically designed for ACCESS. Remote monitoring of any device equipped with an auxiliary contact is possible. Inputs such as the temperature relay of a motor or transformer can be input into the I/O device. Status of any circuit breaker with auxiliary contacts can also be monitored. This is especially useful to monitor MCCB status when metering functionality is not required. The outputs can be used to close contactors, trip circuit breakers, and provide remote indication. In combination with a power meter analog values such as current and voltage can be monitored. Status of the input and output states, counter data, and event log data is communicated to other components of the ACCESS system through an RS-485 serial link.

75

Lighting Control System

Lighting accounts for a large percentage of commercial and industrial power consumption. With a lighting control system, interior and exterior lights can be controlled via override switches, photocells, motion sensors, and a time clock. This will significantly cut energy costs as well as offer a safe and userfriendly environment for occupants. New energy codes are requiring lighting control on a state-bystate basis. ASHRAE 90.1 – 1999 calls for motion sensors, override switches and time clocks for commercial applications. These codes apply to buildings larger than 5000 square feet, non-24 hour operation, and non-emergency operation. California and Wisconsin have already adopted ASHRAE 90.1-1999 and several other states are expected to follow.

76

LCP Products

The LCP (Lighting Control Panel) family of lighting control systems is perfect for commercial applications such as schools, recreation centers, fast food, office buildings, prisons, and a variety of other applications. Depending on the specific LCP product, a lighting control panel can have up to 32 inputs and outputs. Four models are available: LCP 500, LCP 1000, LCP 1500, and LCP 2000. The LCP comes fully assembled with all specified relays in a NEMA 1 enclosure.

Time Clock and Keypad

The Siemens LCP also includes an astronomical clock for controlling timed events. Self-prompting instructions on an LCD screen make programming easy. A keypad is used to enter instructions for lighting circuit control. Optional EZ CONFIG software allows programming of a single cabinet or an entire lighting control network locally or via modem.

77

System Accessories

Several accessories are available to enhance the operation of LCP products. A photocell can be used to control lights based on the amount of ambient light in an area. Touch-tone phone control (LCP TIM) allows you to use any phone to override the lighting. The LCP 2000 seamlessly integrates with HVAC and building management systems via the ModBus gateway. This integration allows control by other systems of each individual LCP relay or group of relays from a single RS-485 connection. Up to 127 LCP’s can be on a single network.

VISION TOUCH

VISION TOUCH software, working in conjunction with LCP PC programming software, provides a graphical interface of a lighting system. Once panels have been programmed, VISION TOUCH graphics offer real-time lighting management. Simply touch the area that you wish to control or use a mouse to select one of the preset buttons. Common applications include schools, stadiums, and prisons. In the following example an LCP is used to control lighting of a gym with three basketball courts, a running track, and various exercise areas. VISION TOUCH is available only for the LCP 2000.

78

ACCESS System Application Example

The following illustration shows an example of Siemens ACCESS system including hardware, software, and field devices. In this example Siemens power meters are located throughout the distribution system. Siemens software, WinPM and SIEServe, are used to record voltage, current, power, and harmonic events for use in other parts of the system. Several other components that make up the ACCESS system such as circuit breakers, SIPROTEC series relays, SAMMS, ethernet converters, and isolated multi-drop converters are also utilized. ACCESS components are installed in Siemens switchboards, switchgear, and motor control centers. Siemens ACCESS devices are also installed in a retrofit application which could have been provided by another manufacturer.

79

Review 6 1.

____________ is a trade name used by Siemens to identify a group of multifunction protection relays.

2.

Siemens Sentron ICCB circuit breakers are available in ratings from 800 to ____________ amps.

3.

Static Trip III overcurrent protective devices for use on Type ____________ low-voltage power circuit breakers.

4.

Static Trip ____________ features extended protective relaying. a. III b. IIIC c. IIICP d. IIICPX

5.

____________ is microprocessor-based motor control and protection device.

6.

VisionTouch software is available for use with the ____________ . a. LCP 500 b. LCP 1000 c. LCP 1500 d. LCP 2000

7.

80

The LCP 2000 can have up to ____________ inputs and ____________ outputs.

Review Answers

Review 1

1) f; 2) 60; 3) current; 4) a

Review 2

1) c; 2) 1200; 3) 562.9; 4) b; 5) 1.41; 6) b

Review 3

1) 120; 2) 5; 3) c; 4) K factor; 5) a; 6) Apparent; 7) Power factor; 8) a; 9) d

Review 4

1) a; 2) b; 3) SEABus, SEABus; 4) node; 5) Ethernet converters; 6) 50; 7) 4000; 8) 32

Review 5

1) key; 2) 9300, 9330; 3) 15th; 4) GPS; 5; 9500

Review 6

1) SIPROTEC; 2) 5000; 4) RL; 4) d; 5) SAMMS; 6) d; 7) 32, 32

81

Final Exam


1.

Which of the following is a supervisory device? a. c.

2.

0.707 1.41

b. d.

0.9 2

A ____________ is when there is an increase or decrease in normal line voltage within the normal rated tolerance of the electronic equipment. These are usually short in duration and do not affect equipment performance. a. b. c. d.

82

Incandescent lighting Ballested lighting Variable speed drives Computers

The crest factor of a pure sinusoidal waveform is ____________ . a. c.

4.

WinPM LCP

Which of the following is an example of a linear load? a. b. c. d.

3.

9500 Power Meter b. SIEServe d.

Voltage Swell Undervoltage Outage Voltage Fluctuation

5.

Type ____________ disturbances last up to 0.5 Hz. a. c.

6.

b. d.

2nd 4th

power factor correction capacitors a UPS system K-rated transformers a voltage regulator

9230 4720

b. d.

4300 9500

The ____________ meter includes a front optical data port for accessibility by a portable PC. a. c.

10.

1st 3rd

The ____________ meter has a high resolution graphical display. a. c.

9.

Type II Type IV

To help reduce the effects of harmonics it may be necessary to install ____________ . a. b. c. d.

8.

b. d.

The ____________ harmonic is a positive sequence harmonic. a. c.

7.

Type I Type III

4720 9300

b. d.

9240 4700

An advantage to loop topology over straight-line topology is the ability to ____________ . a. b. c. d.

communicate with each device in the event of a break in the communication cable reduce the amount of communication wire required connect additional field devices have longer runs

83

11.

The rules that govern the communication of the ACCESS system are known collectively as ____________ . a. c.

12.

star all of the above

CBEMA Electronic Industries Association Institute of Electrical and Electronic Engineers U.S. Department of Commerce

SIEBus VISION TOUCH WinPM SIEServe

4 128

b. d.

32 232

____________ protective relays are designed to provide protective relay functions, metering, and control associated with switchgear circuit breaker operation. a. c.

84

b. d.

One Isolated Multi-Drop Converter can handle up to ____________ field devices. a. c.

16.

bus combination

____________ software provides a graphical interface of a lighting system when used with an LCP 2000. a. b. c. d.

15.

SEABus Profibus DP

____________ developed RS-232 and RS-485 standards. a. b. c. d.

14.

b. d.

A LAN can be arranged with nodes in a ____________ configuration. a. c.

13.

DNP 3.0 ModBus

SIPROTEC S7/IO

b. d.

LCP 2000 SAMMS

17.

The Static Trip ____________ provides basic overcurrent protection, metering, and extended protective relaying. a. c.

18.

IIIC IIICPX

SAMMS Static Trip III

b. d.

SIPROTEC Sensitrip

Which of the following meters does not feature harmonic analysis? a. c.

20.

b. d.

____________ is a motor control protection device a. c.

19.

III IIICP

9300 9230

b. d.

4700 9500

Which of the following meters features GPS time synch? a. c.

9230 9330

b. d.

9500 4720

85

Notes

86

Notes

87

Notes

88

Table of Contents

Introduction ..............................................................................2 Distribution Systems ................................................................4 Panelboards ..............................................................................6 Overcurrent Protective Devices .............................................. 12 Panelboard Construction......................................................... 17 Types of Panelboards ..............................................................26 Individual Overcurrent Protection ...........................................31 Power Supply Systems ...........................................................36 Service Entrance Panelboards ................................................40 Panelboard Grounding ............................................................43 Ground Fault Protection ..........................................................48 Panelboard Ratings .................................................................50 P1, P2, and P3 Panelboards ....................................................53 Transient Protection System (TPS)..........................................59 P4 and P5 Panelboards ...........................................................63 Telephone and Equipment Panelboards .................................68 Seismic Rated Panelboards ....................................................69 Accessories ............................................................................70 Catalog Numbers ....................................................................73 Information Needed to Order Panelboards .............................75 Review Answers .....................................................................77 Final Exam ..............................................................................78

1

Introduction

Welcome to another course in the STEP series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Panelboards and related products. Upon completion of Panelboards you will be able to:

2

•

Explain the role of panelboards in a distribution system

•

Define a panelboard according to the National Electrical Code®

•

Distinguish between a lighting and appliance panelboard versus a power and distribution panelboard

•


•

Identify various components of a Siemens panelboard

•

Distinguish between a main breaker and main lug only panelboard

•

Identify various power supply systems

•

Explain the use of panelboards used as service-entrance equipment

•

Describe the proper grounding techniques of service entrance and downstream panelboards

•

Identify various ratings of Siemens panelboards

•

Identify panelboard accessories

This knowledge will help you better understand customer applications. In addition, you will be able to describe products to customers and determine important differences between products. You should complete Basics of Electricity and Molded Case Circuit Breakers before attempting Panelboards. An understanding of many of the concepts covered in Basics of Electricity and Molded Case Circuit Breakers is required for Panelboards. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. I-T-E, Vacu-Break and Clampmatic are registered trademarks of Siemens Energy & Automation, Inc. Sentron is a trademark of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-2005, National Electrical Code Copyright, 2004, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories Inc. is a registered trademark of Underwriters Laboratories Inc., Northbrook, IL 60062. The abbreviation “UL” shall be understood to mean Underwriters Laboratories Inc. Other trademarks are the property of their respective owners.

3



Most of us are familiar with the distribution system found in the average home. Power, purchased from a utility company enters the house through a metering device. The power is then distributed from a load center to various branch circuits for lighting, appliances, and electrical outlets. Utility Power

Meter

Main Service Disconnect

Load Center Branch Breakers

4

Comercial/Industrial Distribution

Distribution systems used in multifamily, commercial, and industrial locations are more complex. A distribution system consists of metering devices to measure power consumption, main and branch disconnects, protective devices, switching devices to start and stop power flow, conductors, and transformers. Power may be distributed through various switchboards, transformers, and panelboards. Good distribution systems don’t just happen. Careful engineering is required so that the distribution system safely and efficiently supplies adequate electric service to both present and possible future loads. Utility Power

Building

Disconnect

Transformer Outside Switchgear

Switchboard

Motor Control

Power Panelboard

Lighting Panelboard

5

Panelboards

Electrical distribution systems, whether simple or complex, typically include panelboards, the focus of this course. Panelboards provide circuit control and overcurrent protection.

Panelboard Definition

6

The National Electrical Code® (NEC®) defines a panelboard as a single panel or group of panel units designed for assembly in the form of a single panel; including buses, automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall or partition and accessible only from the front (Article 100definitions).

According to the NEC® definition, panelboards are: •

Used to control light, heat, or power circuits

•

Placed in a cabinet or cutout box

•

Mounted in or against a wall

•

Accessible only from the front

Used to Control Light, Heat, or Power Circuits Placed in a Cabinet or Cutout Box

Mounted in or Against a Wall

Accessible Only From the Front

1.75 in. (44 mm) 0.25 in. (6 mm)

Note: Article 408 in the National Electrical Code® covers panelboards. You are encouraged to become familiar with this material. Panelboards basically fall into two categories: •

Lighting and appliance branch-circuit panelboards

•

Power panelboards


7

Lighting and Appliance Branch-Circuit Panelboard

In order to understand the difference between a lighting and appliance branch-circuit panelboard and a power panelboard we must look at NEC® Articles 408.34 and 408.35. The NEC® states that a lighting and appliance branch circuit has a connection to the neutral of the panelboard and has overcurrent protection of 30 amperes or less in one or more conductors. A neutral is a current-carrying component that is connected to the third wire of a single-phase, three wire system or the fourth wire of a three-phase, four wire system. For example, the following illustration shows the secondary of a 480 volt, wyeconnected, three-phase transformer. There is 480 volts between phases and 277 volts between any phase and neutral (N). A

277 Volts

480 Volts B

277 Volts 480 Volts

480 Volts

Neutral (N) 277 Volts

C

From Article 408.34 we can determine that a lighting and appliance branch-circuit panelboard must have:

Number of Overcurrent Devices

1.

More than 10% of the overcurrent devices (poles) must be protecting lighting and appliance branch circuits rated 30 amps or less.

2.

A neutral connection must be provided.

Once a panelboard has met the two previous conditions required of a lighting and appliance branch-circuit panelboard, a third condition exists in the NEC® 408.35. 3.

A maximum of 42 overcurrent devices (poles) are allowed in any one cabinet or enclosure.

Note: Article 408.34 and 408.35 are application rules that applies to all panelboard types, regardless if the manufacturer calls them a distribution panelboard or a lighting panelboard by description.

8

Class CTL

In addition to the 42 overcurrent device rule, Article 408.15 states that a lighting and appliance branch-circuit panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and approved. Class CTL is a designation used by Underwriters Laboratories, Inc. (UL 67), to designate panelboards and circuit protection devices which meet the NEC® code. Class CTL panelboards, such as Siemens P1, P2, and P3 panelboards, incorporate physical means that prevent the installation of more overcurrent devices than the panelboard is designed and rated.

Overcurrent Devices

Each pole of a circuit breaker is considered one overcurrent device. For example, a 1-pole breaker is one overcurrent device and a 2-pole breaker is two overcurrent devices.

1-Pole Circuit Breaker One Overcurrent Device

2-Pole Circuit Breaker Two Overcurrent Devices


9

Example

In the following example, a three-phase, four-wire (the fourth wire is neutral) distribution system is used to supply a panelboard. The panelboard has five 1-pole, 15 A breakers; twenty-one 1-pole, 20 A breakers; and eight 2-pole, 40 A breakers for a total of 42 overcurrent devices. Ten percent or more of these overcurrent devices must be rated for 30 amps or less. In this example five overcurrent devices are required (10% of 42 = 4.2). There are 26 overcurrent devices rated at 30 amps or less. This is a lighting and appliance panelboard branch-circuit panelboard. Number of Circuit Breakers 5 21 8

Description 1-Pole, 15 A 1-Pole, 20 A 2-Pole, 40 A

Number of Overcurrent Devices 5 21 16 42

Power Panelboards

NEC® Article 408.34(B) defines a power panelboard as one having 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch circuits. It can be said that panelboards that are not lighting and appliance branch-circuit panelboards are power panelboards.

Example

In the following example there are only four overcurrent devices which are rated at 30 amps or less. This panelboard does not qualify as a lighting and appliance panelboard. It is a power and distribution panelboard. Number of Circuit Breakers 4 22 8

Description 1-Pole, 30 A 1-Pole, 40 A 2-Pole, 40 A



10

Review 1 1.

A ____________ ____________ distributes electrical power throughout a building.

2.

Which of the following does not meet the NEC® definition for a panelboard? a. controls light, heat, or power circuit b. accessible from the front or back c. mounted in or on a wall d. placed in a cabinet or cutout box

3.

Article ____________ in the National Electrical Code® covers panelboards.

4.

The following is an example of a ____________ and ____________ panelboard.

Number of Circuit Breakers

Description

2 4 4

3-Pole, 60 A 2-Pole, 30 A 1-Pole, 15 A


Why? ________________________________________

11

Overcurrent Protective Devices

Excessive current is referred to as overcurrent. The National Electrical Code® defines overcurrent as any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault (Article 100-definitions). Current flow in a conductor always generates heat. The greater the current flow, the hotter the conductor. Excess heat is damaging to electrical components. For that reason, conductors have a rated continuous current carrying capacity or ampacity. Overcurrent protection devices are used to protect conductors from excessive current flow. These protective devices are designed to keep the flow of current in a circuit at a safe level to prevent the circuit conductors from overheating.

Normal Current Flow

Excessive Current Flow


12

Circuit protection would be unnecessary if overloads and short circuits could be eliminated. Unfortunately, overloads and short circuits do occur. To protect a circuit against these currents, a protective device must determine when a fault condition develops and automatically disconnect the electrical equipment from the voltage source. An overcurrent protection device must be able to recognize the difference between overcurrents and short circuits and respond in the proper way. Slight overcurrents can be allowed to continue for some period of time, but as the current magnitude increases, the protection device must open faster. Short circuits must be interrupted instantly. Fuse

A fuse is a one-shot device. The heat produced by overcurrent causes the current carrying element to melt open, disconnecting the load from the source voltage.

Nontime-Delay Fuses

Nontime-delay fuses provide excellent short circuit protection. When an overcurrent occurs, heat builds up rapidly in the fuse. Nontime-delay fuses usually hold 500% of their rating for approximately one-fourth second, after which the currentcarrying element melts. This means that these fuses cannot be used in motor circuits which often have inrush currents greater than 500%.

Time-Delay Fuses

Time-delay fuses provide overload and short circuit protection. Time-delay fuses usually allow five times the rated current for up to ten seconds to allow motors to start.

13

Fuse Classes

Fuses are grouped into classes based on their operating and construction characteristics. Each class has an ampere interrupting capacity (AIC) which is the amount of fault current they are capable of interrupting without destroying the fuse casing. Fuses are also rated according to the maximum continuous current and maximum voltage they can handle. Underwriters Laboratories (UL) establishes and standardizes basic performance and physical specifications to develop its safety test procedures. These standards have resulted in distinct classes of low voltage fuses rated at 600 volts or less. Class H K R J L

Class R Fuseholder

AIC Rating 10,000 A 50,000 A 200,000 A 200,000 A 200,000 A

An optional Class R fuseholder can be used to prevent any other type of fuse from being used. The Class R rejection clip contains a pin that permits only the notched Class R fuse to be inserted. This prevents a lower rated fuse from being used.

Notch Pin Rejection Clip

Fusible Disconnect Switch

14

A fusible disconnect switch is one type of device used on panelboards to provide overcurrent protection. Properly sized fuses located in the switch open when an overcurrent condition exists.

Circuit Breakers

Another device used for overcurrent protection is a circuit breaker. The National Electrical Code® defines a circuit breaker as a device designed to open and close a circuit by nonautomatic means, and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. Circuit breakers provide a manual means of energizing and deenergizing a circuit. In addition, circuit breakers provide automatic overcurrent protection of a circuit. A circuit breaker allows a circuit to be reactivated quickly after a short circuit or overload is cleared. Unlike fuses which must be replaced when they open, a simple flip of the breaker’s handle restores the circuit.


15

Ampere Rating

Like fuses, every circuit breaker has a specific ampere, voltage, and fault current interruption rating. The ampere rating is the maximum continuous current a circuit breaker can carry without exceeding its rating. As a general rule, the circuit breaker ampere rating should match the conductor ampere rating. For example, if the conductor is rated for 20 amps, the circuit breaker should be rated for 20 amps. Siemens I-T-E® breakers are rated on the basis of using 60° C or 75° C conductors. This means that even if a conductor with a higher temperature rating were used, the ampacity of the conductor must be figured on its 60° C or 75° C rating. There are some specific circumstances when the ampere rating is permitted to be greater than the current carrying capacity of the circuit. For example, motor and welder circuits can exceed conductor ampacity to allow for inrush currents and duty cycles within limits established by NEC®. Generally the ampere rating of a circuit breaker is selected at 125% of the continuous load current. This usually corresponds to the conductor ampacity which is also selected at 125% of continuous load current. For example, a 125 amp circuit breaker would be selected for a load of 100 amps.

Voltage Rating

The voltage rating of the circuit breaker must be at least equal to the circuit voltage. The voltage rating of a circuit breaker can be higher than the circuit voltage, but never lower. For example, a 480 VAC circuit breaker could be used on a 240 VAC circuit. A 240 VAC circuit breaker could not be used on a 480 VAC circuit. The voltage rating is a function of the circuit breakers ability to suppress the internal arc that occurs when the circuit breaker’s contacts open.


Circuit breakers are also rated according to the level of fault current they can interrupt. When applying a circuit breaker, one must be selected which can sustain the largest potential short circuit current which can occur in the selected application. Siemens circuit breakers have interrupting ratings from 10,000 to 200,000 amps. To find the interrupting rating of a specific circuit breaker refer to the Speedfax catalog.


16

Panelboard Construction

Panelboards are available in different sizes with variations in construction. The components that make up a panelboard, however, are similar. Panelboards contain a can, interior, circuit protection devices, label, and trim. Can

The can is typically constructed of galvanized steel and houses the other components. The can is also referred to as the box or an enclosure. It is designed to provide component and personnel protection. Removable blank end panels allow the user to cut whatever conduit holes are necessary. Prestamped knockouts are available as an option. Mounting studs are used to support the interior or group mounted devices.

Can

Mounting Stud Removable End Panel

17

Interior

The interior consists of several components, including overcurrent protection devices, bus bars and insulated neutral bus bars. The interior is mounted to the four mounting studs in the can. Jacking screws (not shown) allow adjustment of the interior within the enclosure.

Bus Bars

A bus bar is a conductor that serves as a common connection for two or more circuits. It is represented schematically by a straight line with a number of connections made to it. NEC® article 408.3(A)(1) states that bus bars shall be located so as to be free from physical damage and shall be held firmly in place. Standard bus bars on Siemens panelboards are made of aluminum, but copper bus bars are available as an option. Bus Bar

Branch Circuits


18

NEMA Arrangement

Bus bars are required to have phases in sequence so that an installer can have the same fixed phase arrangement in each termination point in any panelboard or switchboard. This is established by NEMA (National Electrical Manufacturers Association). It is possible to have a non-NEMA phase sequence which would have to be marked on the panelboard. It is assumed that bus bars are arranged according to NEMA. The following diagram illustrates accepted NEMA phase arrangements.

Vertical (Left-to-Right)

High Leg

Horizontal (Top-to-Bottom)

Although we have not yet talked about various power supplies to a panelboard, it should be noted that some power supply systems use a transformer with a three-phase, four-wire (3Ø4W), delta-connected secondary. On these systems the secondary voltage of one phase is higher than the other two phases. This is referred to as the high leg. NEC® Article 215.8 requires that the high leg bus bar or conductor be permanently marked with a finish that is orange in color. Four-wire, deltaconnected transformers should always be wired so that the B phase is the high leg. More information on calculating the value of the high leg, as well as connecting loads, is discussed later in the course.

High Leg

Vertical

Horizontal

19

Split Neutral

An insulated neutral bus is provided. In many instances it is a split neutral, meaning that an equal number of neutral connections are available on both sides of the panelboard. Split neutrals are connected together through a bus bar. Insulation separates the neutral bus from the power supply bus bars. Service Neutral Lug

Neutral Bus Bar

Branch Neutral Lugs

Insulation Supply Bus Bars

200% Neutral

Some loads can cause harmonics and non-linear loading on a distribution system. This requires special consideration when ordering a panelboard. One way to deal with non-linear loads is to double the capacity of the panelboard neutral. A 200% neutral is an available option on Siemens panelboards.

Circuit Protection Devices

Circuit protection devices mount directly to the bus bars. In the following illustration for example, a BL circuit breaker is mounted to the panelboard bus.

BL Type Circuit Breaker

Bus Bars

20

Circuit Identification

Circuits must be clearly labeled. Poles arranged with odd numbers on the panelboard’s right (your left) and even numbers on the panelboard’s left (your right) is referred to as NEMA numbering. In some areas a vertical sequence is required. In addition a directory card is placed in a holder which is attached to the inside of the door.

NEMA Numbering

Label

Vertical Numbering

The label identifies the panelboard’s type, voltage rating, and ampacity.

System Panel Type 208Y/120 V P1 250 Amps Max (see main device or breaker)

Provisions are for device types: 100 A max: BL BLH HBL BLF BLHF BLE BLEH LG BAF BAFH BQD Minimum size UL listed cabinet or cut-out box for this panel: 20”W x 5.75”DP x 56”H

Siemens Energy & Automation, Inc. Atlanta, Ga. USA For emergency service call 1-800-241-4453

15-A-1034-01 Rev.2

21

Dead Front and Trim

The dead front and trim are the front surfaces of the panelboard that cover the interior. The trim includes an access door. These components provide access to the overcurrent devices while sealing off the bus bars and internal wiring from contact.

Access Door

Trim

Dead Front

Filler Plates

QF3 filler plates are used to cover any unused pole spaces not filled by a circuit breaker.

Circuit Breaker QF3 Filler Plate

22

Enclosures

The National Electrical Manufacturers Association (NEMA) has established guidelines for electrical equipment enclosures. Siemens panelboards are supplied as standard in a NEMA Type 1 enclosure intended for general purpose indoor use.

The following enclosures are available as an option: Type 3R

Enclosures are intended for outdoor use primarily to provide a degree of protection against rain, sleet and damage from external ice formation.

Type 4X

Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water, hose-directed water, and damage from external ice formation.

Type 3R/12

Enclosures are intended for indoor use primarily to provide a degree of protection against circulating dust, falling dirt, and dripping noncorrosive liquids.

23

Installation

Panelboard installation requires careful planning to ensure a safe environment for personnel and equipment. Article 110.26 of the National Electrical Code® covers spaces about electrical equipment, such as panelboards. The intent of Article 110.26 is to provide enough working space for personnel to examine, adjust, service, and maintain energized equipment. Article 110.26 divides the three parts of a safe working space environment into depth, width, and height. In addition, Article 110.26 discusses entrance requirements to the working space as well as requirements for dedicated equipment space for indoor and outdoor applications. It is beyond the scope of this course to discuss in detail the requirements of Article 110.26. You are, however, encouraged to become familiar with it.


24

Review 2 1.

A ____________ is a conductor that serves as a common connection for two or more circuits.

2.

Circuit protection devices are designed to keep the flow of ____________ in a circuit at a safe level to prevent the circuit conductors from overheating.

3.

Three causes of overcurrent are: a. ____________ b. ____________ c. ____________

4.

A Class K fuse has an ampere interrupting capacity of ____________ amps.

5.

A Class ____________ fuse has a notch to fit a rejection clip.

6.

Circuit breakers are rated for continuous ____________ , ______________, and fault current interruption capacity.

7.

The panelboard components designed to seal off the bus bars and internal wiring from contact are the ____________ and ____________ .

8.

Siemens panelboards are supplied standard in a NEMA Type ____________ enclosure.

25

Types of Panelboards

There are two types of panelboards, main breaker and main lug only. Main Breaker

Line Side Terminals

Main Breaker Type Panelboard

Main Lug Only

Main Bus Bars

The incoming supply cables of a main breaker type panelboard are connected to the line side of the main breaker, which in turn feeds power to the panelboard and its branch circuits. The main breaker disconnects power from the panelboard and protects the system from short circuits, overloads and ground faults if equipped with ground fault protection. Siemens main breakers are bus connected to the main bus bars. This means there are no cable connections required from the main circuit breaker to the lugs on the main bus bars. Bus connecting provides a higher degree of circuit integrity because there is less chance for loose connections which lead to overheating.

Bus Connected

26

Depending on the panelboard the main breaker can either be mounted horizontally or vertically. Supply

Supply

To Branch Circuit

Main Breaker Main Breaker

Branch Breaker Branch Breaker

Main Breaker Mounted Horizontally

Main Lug Only

Main Breaker Mounted Vertically

A main lug only type panelboard does not have a main circuit breaker. The incoming supply cables are connected directly to the bus bars. Primary overload protection for the panelboard is not provided as an integral part of the panelboard.

27

Feed-Through Lugs

There are a variety of ways a main breaker or main lug only panelboard might be used. For example, a lighting and appliance branch-circuit panelboard can have a maximum of 42 poles. If more branch circuits were required an additional panelboard could be used. Feed-through lugs are used to connect a main breaker and main lug only panelboard when they are mounted adjacent to each other. A main breaker panelboard uses feedthrough lugs mounted on the main bus of the panelboard and interconnecting cables are routed to the main lug only panelboard. The main breaker protects both panelboards from overcurrent. Supply

Main Breaker

Feed-Through Lugs

28

Sub-Feed Lugs

Sub-feed lugs are used to connect two main lug only panelboards that are mounted adjacent to each other. For example two main lug only panelboards might be supplied by a circuit breaker or fused disconnect. Power supplied by the overcurrent protection device are routed to the first panelboard. The power is routed to the second panelboard through sub-feed lugs. Incoming Feeder Cables

Fused Disconnect Switch or Circuit Breaker

Sub-Feed Lugs

29

Unit Space and Number of Circuits

Unit space is the area that accommodates the branch circuit breakers in most power panelboards. The number of branch circuits determines the panel dimensions in lighting and appliance branch-circuit panelboards.

10”

Branch Circuit Breaker

60”

Unit Space

Power Panelboard Unit Space

Lighting and Appliance Branch-Circuit Panelboards Number of Circuits

When an application requires a circuit breaker that is a larger frame size than the branch circuit breakers available and will not fit in the branch circuits location, a subfeed breaker can be used. One possible application is to supply a second panelboard located some distance from the first panelboard. This is, however, not the only application. A subfeed breaker can supply any load that a branch circuit breaker can supply.

Main Breaker

Sub-Feed Breaker

30

Individual Overcurrent Protection

The National Electrical Code® requires panelboards to be individually protected against overcurrent. Main overcurrent protection may be an integral part of a panelboard or located remote from the panelboard. NEC® Article 408.36 states that each lighting and appliance branch-circuit panelboard shall be individually protected on the supply side by not more than two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. Individual Protection

The following illustration shows two possible ways individual panelboard overcurrent can be accomplished. A main circuit breaker can be located as an integral part of the panelboard or can be located remotely. In this example the main breaker and panelboard are both rated for 600 amps. Supply Supply

600 Amp Breaker

600 Amp Panelboard Main Overcurrent Protection as Integral Part of Panelboard

600 Amp Breaker

600 Amp Panelboard Main Overcurrent Protection Remote From Panelboard


31

Split Bus

Panelboards can have as many as two main circuit breakers or two sets of fuses to protect. When two main circuit breakers are used in a panelboard a split bus is used. Half of the branch circuits are protected by one main circuit breaker and half protected by the other main circuit breaker. 150 Amp Service

100 Amp Breaker

100 Amp Breaker

150 Amp Main Breaker

32

Exception to NEC® 408.36

There is an exception to NEC® Article 408.36. Exception No. 1: Individual protection for a lighting and appliance panelboard shall not be required if the panelboard feeder has overcurrent protection not greater than the rating of the panelboard. The following illustration shows two panelboards protected by a single 600 Amp fused disconnect switch. Note that the fused disconnect feeder provides overcurrent protection not greater than the rating of the panelboards. Incoming Feeder Cables

600 Amp Fused Disconnect Switch

600 Amp Panelboard

600 Amp Panelboard


33

Panelboard Supplied by a Transformer

Frequently a panelboard is supplied by the secondary of a transformer. According to NEC® Article 408.36(D), individual protection for the panelboard must be provided on the secondary side of the transformer. The overcurrent protection device can be installed either ahead of or in the panelboard. Transformer

Transformer

Neutral Bus Panelboard Neutral Bus Panelboard Overcurrent Protection Provided in Panelboard

Overcurrent Protection Provided Ahead of Panelboard

The NEC® makes an exception to this rule. A panelboard supplied by a single-phase transformer having a 2-wire (single-voltage) secondary can be protected by an overcurrent protection device located on the primary side of the transformer.


34

Review 3 1.

The two types of panelboards are main ____________ and main ____________ only.

2.

The main breaker of a main breaker panel can be mounted ____________ or ____________ .

3.

Primary overload protection for a main ____________ type panelboard is not provided as an integral part of the panelboard.

4.

____________ - ____________ lugs are used to connect a main breaker and main lug only panelboard when they are mounted adjacent to each other.

5.

The NEC® article that covers individual overcurrent protection for panelboards is ____________ .

6.

A lighting and appliance branch-circuit panelboard can have as many as ____________ main circuit breakers or sets of fuses to protect it.

35

Power Supply Systems

Panelboards receive power from a variety of sources. Downstream panelboards may receive power from upstream panelboards or switchboards, however, power for the distribution system originates from a utility power company. Power from the power company is stepped down through transformers to be distributed in residential, commercial and industrial locations. Several systems are used. The following are some examples of systems in use that are suitable for Siemens panelboards. 1Ø3W System

The following diagram illustrates one of the most common single-phase, three-wire (1Ø3W) distribution systems in use today. There are 120 volts between any phase and neutral and 240 volts between phases. Primary

N 120 Volts 240 Volts

36

120 Volts

N

3Ø4W Wye-Connected Transformer

The following illustration shows the secondary of a 480 Y/277 V three-phase, four-wire (3Ø4W), wye-connected transformer. The “480 Y” indicates the transformer is wye-connected and has 480 volts between any two phases. The “277 V” indicates there are 277 volts between any phase and neutral (N). Phaseto-phase voltage is 1.732 times phase-to-neutral voltage (277 x 1.732 = 480). A 480 Volts 480 Volts

N

B 480 Volts C

277 Volts

A-B B-C C-A A-N B-N C-N

480 Volts 480 Volts 480 Volts 277 Volts 277 Volts 277 Volts

37

3Ø4W Delta-Connected Transformer

A three-phase, four-wire (3Ø4W), delta-connected secondary works a little differently. The following illustration shows a delta-connected secondary with 240 volts phase-to-phase. The midpoint of one phase winding is grounded to provide 120 volts between phase A and neutral and 120 volts between phase C and neutral. Between phase B and neutral, however, the voltage is 208 volts. This is referred to as the high leg. Four-wire, deltaconnected transformers should always be wired so that the B phase is the high leg. The high leg can be calculated by multiplying the phase A to neutral voltage times 1.732 (120 x 1.732 = 208). Single-pole breakers should not be connected to the high leg. NEC® Article 110.15 requires that the high leg bus bar or conductor be permanently marked with a finish that is orange in color. This will help prevent electricians from connecting 120 volt singlephase loads to the 208 volt high leg. A

N 240 Volts

B 208 Volts

C

240 Volts

240 Volts

120 Volts

A-B B-C C-A A-N B-N C-N

240 Volts 240 Volts 240 Volts 120 Volts 208 Volts 120 Volts

“B” Phase Bus Bar


38

Not all panelboards are suitable for use on a high leg system. Siemens P1, P2, P3, P4 and P5 panelboards are available for use on a high leg system. Circuit Breakers on the High Leg

It is important to note that not all circuit breakers are suitable for use on the high leg. For example, breakers rated for 240/120 volts can be installed on legs rated for 120 volts, but cannot be installed on the high leg (208 volts).

39

Service Entrance Panelboards

Sometimes panelboards are used as service entrance equipment for a building. This is the equipment located near where the power supply enters the building. The incoming power supply is connected to this equipment which provides a means to control and cut off the supply. The National Electrical Code® discusses service entrance equipment in Article 230. Panelboards used as service entrance equipment must be approved and labeled as such. All Siemens Sentron™ Series panelboards are factory labeled as suitable for service entrance equipment when NEC® requirements are met.

Transformer

Service Entrance Panelboard

Meter

40

Maximum Number of Disconnects

Service-entrance conductors must have a readily accessible means of being disconnected from the power supply. NEC® Article 230.71(A) specifies that for each set of service entrance conductors no more than six switches or circuit breakers shall be used to disconnect and isolate the service from all other equipment. There are two ways panelboards can be configured to meet this requirement. In one example, a main breaker panelboard is used. A single main circuit breaker will disconnect power to all equipment being supplied by the service. In another example, a main lug only panelboard is equipped with up to six circuit breakers to disconnect power to all equipment being supplied by the service. In any case, the circuit breaker must be clearly labeled for the load it supplies.

Main Breaker with Branch Circuits

Main Lug Only with Six Service Disconnects

41

Single-Pole Units

NEC® Article 230.71(B) states that two or three single-pole switches or circuit breakers, capable of individual operation, shall be permitted on multiwire circuits, one pole for each ungrounded conductor, as one multiple disconnect, provided they are equipped with “handle ties” or a “master handle” to disconnect all conductors of the service with no more than six operations of the hand. It is important to note that the “six disconnect rule” refers to the number of disconnects and not the number of poles. For example, the main lug only panelboard shown below has 18 poles but only six circuit breakers. Three poles are mechanically linked together to form one disconnect device. In the illustrated configuration the service can be disconnected with no more than six operations of the hand. This arrangement meets the “six disconnect rule”.


42

Panelboard Grounding

Grounding is an important aspect of any electrical equipment and must be considered carefully. Article 250 of the NEC® covers mandatory grounding requirements. The National Electrical Code® defines ground as a conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth. The following illustration, for example, shows the neutral (N) conductor of a wye-connected transformer connected to ground.

N

Ground

There are two objectives to the intentional grounding of electrical equipment: •

Keep potential voltage differentials between different parts of a system at a minimum which reduces shock hazard.

•

Keep impedance of the ground path to a minimum. The lower the impedance the greater the current is in the event of a fault. The greater the current the faster an overcurrent device will open.

43

Service Entrance Grounding

The circuit is grounded only at the service entrance, never at any downstream equipment. In the following illustration the neutral is grounded at the service equipment by connecting a grounding electrode conductor from the neutral (grounded conductor) to a grounding electrode. The neutral and the panelboard enclosure are bonded together at the service equipment so that the enclosure is also connected to ground through the grounding electrode connector. Panelboard (Service Entrance) Power Source

N

Neutral Bus

Neutral Bonded to Can Grounding Electrode Conductor

Wall Grounding Electrode

44

Equipment Grounding Bus

A panelboard may also require an equipment grounding bus which is non-insulated and mounted inside the panelboard directly to the can. All feeder and branch circuit equipment that are connected to the equipment grounding bus are at the same potential as the panelboard can. Siemens panelboards come with an equipment grounding bus. Equipment Grounding Bus

Grounding Panelboards Downstream

The neutral (grounded conductor) is only connected to ground at the service entrance. Beyond the service equipment the neutral is always insulated. When a downstream panel is used the neutral is insulated in that panel. As shown in the following illustration the enclosure of the downstream panel is connected to ground through a grounding conductor back to the service equipment. Power Source

Panelboard (Service Entrance)

Main

Panelboard (Downstream)

Sub-Feed

Branch

N Neutral Equipment Ground

Equipment Ground Bonded to Can

Insulated Neutral Bonded to Can

Load #1

Load #2

45

Fault Path

In the following illustration load #2 has become shorted to its metal enclosure. Fault current is returned to the source through the path indicated. With a properly coordinated system the branch circuit breaker in the downstream panelboard will open removing the load from the power source. For a discussion of circuit breaker coordination refer to the STEP course, Molded Case Circuit Breakers. Power Source

Panelboard (Service Entrance)

Main

Panelboard (Downstream)

Sub-Feed

Branch

N Neutral Equipment Ground

Insulated Neutral Bonded to Can

Equipment Ground Bonded to Can Short to Ground Load #1

46

Load #2

Review 4 1.

If the secondary of a four-wire, wye-connected transformer is 480 volts phase-to-phase, the phase to neutral voltage is ____________ volts.

2.

If the secondary of a four-wire, delta-connected transformer is 240 volts phase-to-phase, the phase to neutral voltage is ____________ volts from A-N ____________ volts from B-N ____________ volts from C-N

3.

According to NEC® Article 230.71(A), the maximum number of circuit breakers that can be used to disconnect and isolate the service from all other equipment is ____________ .

4.

____________ is the permanent joining of metallic parts to form an electrically conductive path.

5.

The ____________ conductor is grounded only at the service entrance equipment, never at any downstream equipment.

47


In addition to ensuring equipment is properly grounded, ground fault protection for people and equipment is also a concern. NEC® Article 230.95 states that ground-fault protection of equipment shall be provided for solidly grounded wye electrical services of more than 150 volts to ground but not exceeding 600 volts phase-to-phase for each service disconnecting means rated 1000 amperes or more. Although ground-fault protectors are not required on service disconnects that are less than 1000 amperes, they still may be desirable. Ground fault interrupters designed to provide life protection must open a circuit at 5 milliamps (± 1 milliamp). Equipment protection must open a circuit when ground fault current reaches 30 milliamps. Ground fault protection is generally incorporated into a special type of circuit breaker. Ground-Fault Sensor Around Bonding Jumper

One way a ground fault protector works is to install a sensor around the insulated neutral bonding jumper. When an unbalanced current from a line-to-ground fault occurs current will flow in the bonding jumper. When the current reaches the setting of the ground-fault sensor the shunt trip opens the circuit breaker, removing the load from the line. A 480 Volts 480 Volts

N

B 480 Volts C Circuit Breaker with Shunt Trip Option

Relay

Bonding Jumper

Ground Fault Sensor

Service Equipment (1000 Amps or More)

48

Ground-Fault Sensor Around all Conductors

Another way a ground fault protector works is with a sensor installed around all the circuit conductors. During normal current flow the sum of all the currents is zero. However, a ground fault will cause an unbalance of the currents flowing in the individual conductors around the sensor. When this current reaches the setting of the ground-fault sensor the shunt trip opens the circuit breaker. A 480 Volts 480 Volts

N

B 480 Volts C Circuit Breaker with Shunt Trip Option

Relay

Service Equipment (1000 Amps or More) Ground Fault Sensor


49

Panelboard Ratings

When selecting panelboards and overcurrent protection devices it is extremely important to know both the maximum continuous amperes and available fault current. NEC® Article 110.9 states: Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current which is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted. Full Rating

There are two ways to meet this requirement. The full rating method is to select circuit protection devices with individual ratings equal to or greater than the available fault current. This means that, in the case of a building with 65,000 amperes of fault current available at the service entrance, every circuit protection device must be rated at 65,000 amperes interrupting capacity (AIC). In the following example, the main circuit breaker and each branch breaker is rated for 65,000 AIC.

Main Breaker (65,000 amps)

Branch Breakers (65,000 amps)


50

Series-Rated

The series-rated concept is that the main upstream circuit protection device must have an interrupting rating equal to or greater than the available fault current of the system, but subsequent downstream circuit protection devices connected in series can be rated at lower values. For example, a building with 42,000 amperes of available fault current might have the breaker at the service entrance rated at 42,000 AIC and additional downstream breakers rated at 18,000 AIC.

HED4 Main Breaker (42,000 amps)

ED4 Feeder Breakers (18,000 amps)

Series-rated breaker combinations must be tested in series in order to be UL listed. Siemens series-rated breakers are listed in the UL “Recognized Components Directory” (yellow books) Volume 1. Selected series-rated breakers are listed in the Speedfax catalog. Your Siemens sales engineer can provide more information on Siemens series-rated circuit breakers. Rating Terms

There are three rating terms that need to be understood when selecting panelboards and appropriate circuit protection devices.

Withstand Rating

Refers to the level of fault current a piece of equipment can withstand without sustaining damage. Siemens panelboards have withstand ratings up to 200,000 amps.

Interrupting Rating

Refers to the current rating a protective device such as a fuse or circuit breaker can safely interrupt. Siemens molded case circuit breakers have interrupting ratings up to 200,000 amps.

Integrated Equipment

Refers to the interrupting rating of the lowest installed device, unless there is a series combination rating, not to exceed the withstand rating of the equipment.

51

Integrated Equipment Short Circuit Rating

The term Integrated Equipment Short Circuit Rating refers to the application of series circuit breakers in a combination that allows some breakers to have lower individual ratings than the available fault current. This is permitted as long as the series combinations shown have been tested and certified by UL. A P2 main breaker (MB) panelboard, for example, can have a main breaker with a maximum continuous ampere rating of 600 amps, branch circuit breakers with ratings from 15-125 amps, and if used on 480Y/277V has a short circuit interrupting rating of 150,000 amps.

Mains Rating Amperes

Branch Rating Amperes

Max Interrupting Rating Symmetrical Amperes 480Y/277V

600

15 - 125

150,000

To select appropriate main and branch circuit breakers refer to the integrated short circuit ratings tables in the Speedfax catalog. Review 5

52

1.

Ground fault protection is required when service disconnecting devices are rated at ____________ or more.

2.

The ____________ rating method requires selecting circuit protection devices with individual ratings equal to or greater than the available fault current.

3.

Devices selected for integrated equipment application must be tested and certified by ____________ .

4.

____________ rating refers to the level of fault current a piece of equipment can withstand without sustaining damage.

5.

____________ rating refers to the current rating a protective device such as a fuse or circuit breaker can safely interrupt.

6.

____________ ____________ refers to the interrupting rating of the lowest installed device, unless there is a series rating, not to exceed the withstand rating of the equipment.

P1, P2, and P3 Panelboards

P1, P2, and P3 panelboards are grouped together in this section because they are similar in construction and function. These panelboards have field convertible mains, which mean the panelboard can be changed from a main circuit breaker to a main lug only in the field. Another advantage is the ability to field change between top and bottom feed. P1, P2, and P3 panelboards feature concealed fasteners and hinges with a flush door lock. P1, P2, and P3 panelboards are designed to be wall mounted.

53

P1 Panelboards

54

P1 panelboards are the smallest panelboards in this product line and can support up to the equivalent of 42 1-pole circuits. P1 panelboards are available to operate on 1Ø2W, 1Ø3W, 3Ø3W, and 3Ø4W systems with voltages up 480/277 VAC and 250 VDC. They can handle a maximum current up to 400 amps with short circuit interruption ratings up to 200,000 amps.

Voltage

120 VAC, 120/240 VAC, 480Y/277 VAC, 125 VDC, 250 VDC

System

1∅2W, 1∅3W, 3∅3W, 3∅4W

Main Lug Only Rating

250 A, 400 A

Main Circuit Breaker Rating

100 A, 225 A, 250 A, 400 A


10,000 - 200,000 AIR

P1 Dimensions

P1 panelboards are 20” wide and 5.75” deep. An optional 24” wide enclosure is available. Panelboard height varies with the number of circuits and current rating.

5.75”

Max Current (Amps)

Max No. of Poles

Height (Inches)

100, 225, 250

18 30 42

32 38 44

400

18 30 42

56 62 68

20” 24” Optional

55

P2 Panelboards

56

P2 panelboards are available in sizes that will handle the equivalent of up to 54 1-pole circuits. P2 panelboards are available to operate on voltages up to 600 VAC and 250 VDC with 1Ø3W, 3Ø3W, and 3Ø4W systems. They can handle a maximum current up to 600 amps with short circuit interruption ratings up to 200,000 amps.

Voltage

600 VAC Maximum, 250 VDC Maximum

System

1∅3W, 3∅3W, 3∅4W,


100 A, 125 A, 225 A, 400 A, 600 A


100 A, 225 A, 400 A, 600 A


10,000 - 200,000 AIR

Dimensions

P2 panelboards are 20” wide and either 5.75 or 7.75” deep. Panelboard height varies with the number of circuits and current rating.

5.75” 100 A 225 A 400 A 600 A

Main Current (Amps)

Max No. of Poles

Height (Inches) Main Breaker

Height (Inches) Main Lug Only

100

18 30 42

23 29 35

23 29 35

125

18 30 42

29 35 41

NA

225*

18 30 42

39, 32, 44 35, 38, 50 41, 44, 56

26 32 38

400*

18 30 42 54

47, 56 53, 62 59, 68 65, 74

32 38 44 50

600*

18 30 42 54

50, 59 56, 65 62, 71 68, 77

38 44 50 56

*Height variations in main breaker panelboards depend on main breaker selected

20”

57

P3 Panelboards

58

The P3 panelboard is a distribution panelboard with a footprint that is a smaller than the P4 and P5 distribution panelboards. It is grouped here because of its similarity to P1 and P2 panelboards. P3 panelboards are available to operate on voltages up to 600 VAC and 250 VDC with 1Ø3W, 3Ø3W, and 3Ø4W systems. They can handle a maximum current up to 800 amps with short circuit interruption ratings up to 200,000 amps.

Voltage

600 VAC Maximum, 250 VDC Maximum

System

1∅3W, 3∅3W, 3∅4W,


250 A, 400 A, 600 A, 800 A


250 A, 400 A, 600 A, 800 A


10,000 - 200,000 AIR

Transient Protection System (TPS)

Need for Circuit Protection

Transients voltage spikes appear on an electrical system as a result of lightning and switching transients. These transients are capable of destroying sensitive electronic equipment in commercial and industrial applications.

Transient Voltage Spikes

The most damaging voltage spikes are caused by lightning strikes. Although lightning strikes on high voltage lines are generally dissipated by utility transmission and arresters, a lightning strike on a power line several miles away still has the potential to cause extensive electrical damage. Damage to expensive electrical equipment can be either instantaneous or cumulative.

59

Number of Thunderstorms

A typical lightning strike consists of 25,000 amps at 30 million volts. The following map shows the approximate mean annual number of days with thunderstorms in the United States.

TPS

Computers and other office equipment are susceptible to the high energy levels caused by an electrical surge, whether it is caused by electrical equipment or lightning. Any component between the source of the surge and ground can be damaged. Siemens TPS transient protection system clamps these damaging voltage spikes before they damage expensive and sensitive equipment.

TPS

60

Installation

The TPS is bolted directly to the bus bars within the P1 panelboards. Purchased “over the counter” and utilizing a field installation kit, the TPS transient voltage protection system can easily be mounted in existing P1 lighting panelboards. LEDs indicate that the device is working and provide voltage and diagnostic monitoring. There is an audible alarm and test button. Options include a surge counter and a remote monitoring device.

TPS with LED indicatiors, audible alarm with silence switch, and test button.

Clamping Voltage

Clamping voltage is the amount of voltage allowed across a surge suppression device when it is conducting a specific current created by a surge. The following chart indicates clamping voltage for the Siemens TPS.

Peak Current Peak Rating

Peak current rating specifies the maximum current that a protective device can withstand from a single surge. The Siemens TPS can withstand impulse currents as high as 80,000 amps or 160,000 amps, depending on the model.

61

Review 6

62

1.

The maximum number of circuits available on the P1 lighting panelboards is ____________ .

2.

One way to convert a P1 from top to bottom feed is to relocate the main breaker or lug module. Another way is to ____________ the interior.

3.

The maximum voltage of an P1 panelboard is ____________ VAC.

4.

The maximum integrated equipment short circuit rating of a P2 panelboard is ____________ AIR.

5.

The maximum voltage rating for a P1 panelboard is ____________ VAC.

6.

The ____________ ____________ ____________ is used to protect sensitive electrical equipment from damaging voltage spikes.

P4 and P5 Panelboards

P4 and P5 power panelboards are similar in design and features, but vary in the ratings available. P4 and P5 panelboards will accept various circuit breakers and fusible switches. P4 will accept branch circuit breakers up to 600 amps. The P5 will accept branch circuit breakers up to 1200 amps.

63

Panelboard Ratings

The following information gives various P4 and P5 rating ranges. Refer to Siemens Speedfax when ordering specific panelboards. Branch circuit breakers vary depending on the panelboard rating.

P4

Dimensions

P5

Voltage

600 V

600 V

System

1∅3W, 3∅4W, 3∅3W,

1∅3W, 3∅4W, 3∅3W,

Main Lug Only

400 A - 1200 A

800 A, 1000 A, 1200 A

Main Circuit Breaker

400 A - 600 A

800 A, 1200 A

Main Fusible Switch

100 A - 200 A

400 A - 1200 A

Branch Circuit Breakers

All 15 A - 600 A

All 15 A - 1200 A


200,000 AIR Maximum

200,000 AIR Maximum

The P4 is 32” wide by 10” deep. This simplifies handling and installation. The enclosure height varies with the type and number of circuits required. The enclosure heights are 60”, 75”, and 90”.A one piece door is available which allows for locking and flush mounting. The P5 is 38” wide by 12.75” deep in a NEMA Type 1 enclosure. The P5 is 38” wide by 14.25” deep in a NEMA Type 3R or 12 enclosure. The enclosure height varies with the type and number of circuits required. The enclosure heights are 60”, 75” and 90”.

64

Fusible Switch

Although many panelboards use circuit breakers, it is important to note that some panelboards, such as the P4 and P5 also use fusible switches. Siemens branch fusible switches are available with ampere ratings from 30 to 1200 amps.

Siemens fusible switches can be fitted with Class J, L, RK1, RK5 or T fuses. The following illustration shows a Class R fuse holder.

65

Clampmatic Action

Siemens Vacu-Break® fusible switches, through 600 A, feature a Clampmatic® action. This action holds the current carrying contact surfaces in a vise-like grip. Heat build-up due to current is minimized. When the switch is moved to the “OFF” position the movable contact snaps from between the jaws providing a quick, clean break. Twin arcs are produced which are smaller and extinguish quicker than a single arc produced by other designs.

Enclosed Arc Chamber

The contacts are surrounded by an enclosed arc chamber which absorbs much of the heat from the arching. The enclosed chamber helps limit oxygen which aids the cooling and rapid extinguishing of the arcs.

66

High Contact Pressure Switch

A high contact pressure (HCP) switch is used on switches rated for 800 A and 1200 A. The HCP switch does not use the VacuBreak® design.

67

Telephone and Equipment Panelboards

Siemens also manufactures telephone and equipment cabinets which conform to requirements of Underwriters Laboratories, Inc. Cabinets are 5.75” deep, 20 or 24” wide and vary in height from 23 to 65”.All telephone and equipment cabinets are preceded by the letters “TC” in the catalog number. The catalog number also reflects the cabinet height. For example, “TCS23B” is a telephone and equipment cabinet that is 23” in height.

68

Seismic Rated Panelboards

Seismic activity occurs throughout the United States and the world. The Uniform Building Code (UBC) specifies ratings for the United States. The following seismic zone map roughly identifies seismic activity areas in the United States. Areas in zones with higher numbers experience greater seismic activity than areas in zones with lower numbers.

Siemens panelboards have undergone extensive seismic testing in order to obtain third party certification. Siemens panelboards will operate in zones 0, 1, 2A, and 2B with no modification. Panelboards that require zone 3 and 4 ratings are available with standard lead times.

UBC Seismic Zone Product S1, S2, S3 P4, P5

0

1

2A

Standard

2B

3

4

Optional

69

Accessories

Accessories add to the performance of a panelboard or adapts the panelboard for specific application requirements. Various accessories are available for Siemens panelboards. Shunt Trip

Some accessories modify the circuit breaker. For example, it is sometimes necessary to trip a breaker from a remote location. If someone were to get caught in a piece of machinery, anyone else can push a “panic button” tripping the breaker. One or all critical circuit breakers may be tripped at the push of a button from a distant control point by use of a shunt trip device. The shunt trip may be part of the main breaker which will shut off the entire panelboard, or part of a branch breaker. The shunt trip device consists of a coil in series with a limit switch. When the circuit breaker contacts are closed, the limit switch is closed. Depressing a customer-supplied pushbutton energizes the shunt trip coil, causing the breaker’s mechanical latch to disengage the trip mechanism and opening the circuit breaker’s contacts. When the circuit breaker’s contacts open, the limit switch also opens, removing power from the shunt trip coil. As with any trip, the breaker must be reset manually.

Limit Switch

Coil

Pushbutton

Customer Supply

70

The following illustration shows how an accessory such as the shunt trip is mounted on its associated breakers.

Shunt Trip Accessory

Shunt Trip Accessory

ED Frame

Time Clocks

Other Sentron Series

Tork, Sangamo or Paragon time clocks are available as an accessory. Time clocks are available in 1 or 2-pole, single or double throw devices, or 3-pole, single throw. They are rated for a maximum of 277 volts.

Tork Time Clock

71

A time clock can be used to turn a branch circuit or an entire panelboard on and off at predetermined times. In the following illustration, for example, a time clock connected to a panelboard is used to turn outside lights on and off on a small commercial building.

Storage

Retail

Time Clock Meter

Panelboard

Lighting Parking

Remote Control Switches

72

ASCO 920 switches are mechanically held, two- or threepole remote control switches may be used as a main circuit disconnect device when an application calls for a switch to daily turn blocks of lighting on and off. ASCO 920 switches are available in 30, 60, 75, 100, 150, 200 and 225 amperes. Siemens also has a type CLM switch (not shown) which is a mechanically held, 20 amp, remote control unit, suitable for all types of lighting loads. It is available in 2, 3, 4, 6, 8, 10 and 12 poles.

Catalog Numbers

To help identify each type of panelboard a catalog number is assigned. The catalog number provides a description of the panelboard. There are eight parts to the standard Sentron™ Series panelboard catalog number. The following figure illustrates a typical catalog number. 1

2

3

4

5

6

7

8

Part 1

Part 1 identifies the type of panel. Panelboard are available in P1, P2, P3, P4, and P5 types. The sample panelboard catalog number shown is a P1 panelboard.

Part 2

Part 2 identifies the voltage and system. The following table shows voltage and system configurations available. C

208Y/120 3Ø4W Wye AC - All

R

415/240 3Ø4W Wye AC - All

E


S


D

240 3Ø3W Delta AC - All

L


F

480 3Ø3W Delta AC - P2, P3, P4, P5

T

230 3Ø3W Delta AC - All

G

600 3Ø3W Delta AC - P2, P3, P4, P5

Z

380 3Ø3W Delta AC - P2, P3, P4, P5

I

347AC - P2, P3, P4, P5

1

24V DC 1 Pole Branches Only (3) - All

B

240/120 3Ø4W Delta BØ High Leg AC - All

2

24V DC 2 Pole Branches Only (3) - All

Q

240/120 3Ø4W Delta CØ High Leg AC - P2, P3, P4, P5

3

48 V DC 1 Pole Branches Only (3) - All

X

120/240 2Ø5W Single Neutral AC - P2, P3, P4, P5

4


A

120/240 1Ø3W Grounded Neutral AC (2) - All

5


H

120 1Ø2W Grounded Neutral AC (2) - All

N

125 V DC 2 Pole Branches Only - All

J

240 1Ø2W no Neutral AC (3) - All

O

125/250V DC 2 Pole Branches Only - All

Y

125 1Ø2W Grounded Neutal AC (2) - P2, P3, P4, P5

P

125/250V DC 2 & 3 Pole Branches - All

Z

500 2W DC - P2, P3, P4, P5

U

120V AC 3Ø3W - All

K


V

24V 3Ø3W Grounded BØ - All

M


73

The panelboard identified in the example is a 208Y/120V, 3Ø4W. This indicates it is rated for a 208 volt wye-connected secondary. There are 208 volts phase-to-phase and 120 volts phase-to-neutral. It is a 3-phase (3Ø) 4-wire (4W) system. A 208 Volts 120 Volts B 120 Volts

208 Volts

N 120 Volts 208 Volts C

Part 3

Part 3 indicates the number of circuits in an P1, P2 or P3 type panelboard. If the panelboard is an P4 or P5 type this number represents the enclosures height in inches. In this example the panelboard is an S1. There are 42 circuits.

Part 4

Part 4 indicates whether the panelboard is a main breaker (2-digit code varies for each different circuit breaker), main lug (ML) or main switch (MS). In this example the panelboard is an FXD6 main breaker (FX).

Part 5

Part 5 indicates the panelboard current rating. The example panelboard is rated for 250 amps.

Part 6

Part 6 indicates the bus material. The following table shows bus materials available. In this example the panelboard has standard aluminum bus bars. A B C D E

= = = = =

Tin Plated Aluminum Temp Rated (standard) 750A/in2 Aluminum (optional) Copper Temp Rated (optional) 1000A/in2 Copper (optional) Silver Plated Copper (optional)

Part 7

Part 7 indicates whether feed location is from the top (T) or bottom (B). In this example the panelboard is top fed.

Part 8

Part 8 indicates whether the panelboard is surface mounted (S) or flush mounted (F). In this example the panelboard is surface mounted.

74

Information Needed to Order Panelboards

When ordering a panelboard several questions need to be answered. 1.

What is the system (voltage, phases, number of wires)?

2.

What is the AIC rating (ampere interrupting capacity)?

3.

What is the NEMA Type enclosure desired?

4.

How many circuits are required?

5.

Does the panelboard need to be suitable for service entrance? Suitable for use on service entrance Labels (SUSE) are available provided NEC®requirements are met. A main lug only panelboard, for example, can only have a maximum of 6 breakers or it violates the 6 disconnect rule.

6.

What amperage is the panelboard rated at?

7.

Will the panelboard be main breaker or main lug only?

8.

What special modifications are needed?

9.

What is the shipping time frame?

10. Is the panelboard to be top or bottom fed? 11.

Is the panelboard to be surface or flush mount?

12. Is the panelboard assembled or unassembled?


75

Review 7 1.

The P4 panelboard will accept branch circuit breakers up to ____________ amps.

2.

The maximum main circuit breaker available for the P5 panelboard is ____________ amps.

3.

P4 and P5 panelboards use ____________ switches for branch circuit protection.

4.

The enclosed arc chamber limits ____________ which aids in the cooling and rapid extinguishing of the arcs.

5.

The maximum main circuit breaker available for P4 panelboards is rated for ____________ amps.

6.

A ____________ ____________ accessory mounts to the circuit breaker and is used to trip a breaker from a remote location.

7.

A letter ___________ in part 2 of a catalog number would indicate a 120/240 volt, 1-phase, 3-wire system.

8.

The number 42 in part 3 of a catalog number for a P1 panelboard indicates the panelboard a. contains 42 circuits b. is 42 inches tall c. is 42 inches wide

76

Review Answers

Review 1

1) distribution system; 2) b; 3) 408; 4) lighting and appliance because there are less than 42 poles and more than 10% are rated 30 amps or less.

Review 2

1) bus; 2) current; 3) overload, short circuit, ground fault; 4) 50,000 amps; 5) R; 6) amps, voltage; 7) deadfront and trim; 8) 1.

Review 3

1) breaker, lug; 2) horizontally or vertically; 3) lug only; 4) feed-through; 5) 408.16; 6) two.

Review 4

1) 277; 2) 120 A-N, 208 B-N, 120 C-N; 3) 6; 4) Bonding; 5) neutral.

Review 5

1) 1000 A; 2) full; 3) UL; 4) Withstand; 5) Interrupting; 6) Integrated Equipment.

Review 6

1) 42; 2) invert; 3) 480; 4) 200,000; 5) 600; 6) Transient Protection System

Review 7

1) 600; 2) 1200; 3) fusible; 4) oxygen; 5) 600; 6) shunt trip; 7) a; 8) a.

77

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. After grading the test, mail the answer sheet in for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. Those receiving a score of less than 70% will be provided a second test. 1.

Which of the following is not a requirement for a lighting and appliance panelboard? a. A neutral connection must be provided. b. A maximum of 42 overcurrent devices are allowed. c. More than 10% of the overcurrent devices must be rated 30 amps or less. d. Must be connected to the secondary of a 4-wire, 3-phase, wye-connected transformer.

2.

Panelboards are covered by NEC® article ____________ . a. 110 c. 408

3.

b. d.

50,000 200,000

The item used to cover any unused pole spaces not filled by a circuit breaker is a ____________ . a. dead front c. trim

78

240 430

The AIC rating of a Class R fuse is ____________ amps. a. 10,000 c. 100,000

4.

b. d.

b. d.

QF3 filler plate label

5.

The type of enclosure intended for outdoor use primarily to provide a degree of protection against rain, sleet and damage from external ice formation is ___________ . a. Type 1 c. Type 4X

6.

230.71 240

main breaker and sub-feed main lug only and sub-feed main breaker and main lug only sub-feed and feed-through

On a three-phase, four-wire, wye-connected transformer with a secondary voltage of 480 volts phase-to-phase, the phase-to-neutral voltage is _________ volts. a. 277 c. 138

9.

b. d.

Two types of panelboards are ____________ . a. b. c. d.

8.

Type 3R Type 3R/12

Electrical installation, including panelboard installation is covered in NEC® Article ____________ . a. 110.26 c. 408.16

7.

b. d.

b. d.

240 480

On a three-phase, four-wire, delta-connected transformer the high leg is ____________ . a. A - N c. C - N

b. d.

B-N A-B

10. The maximum number of switches or circuit breakers used to disconnect and isolate the service from all other equipment on service-entrance equipment is ________ . a. 1 c. 4

b. d.

2 6

79

11.

The neutral conductor is ____________ grounded at the service-entrance panelboard. a. always c. rarely

b. d.

never often

12. The neutral conductor is ____________ grounded at panelboards downstream from the service-entrance panelboard. a. always c. rarely

b. d.

never often

13. Article 230.95 of the NEC® states that ground-fault protection of equipment shall be provided for solidly grounded wye electrical services of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase for each service disconnecting means rated ____________ amperes or more. a. 5 milliamps c. 1000 amps

b. d.

10 amps 200,000 amps

14. The rating which refers to the interrupting rating of the lowest installed device, unless there is a series combination rating, not to exceed the withstand rating of the equipment is the ____________ rating. a. full c. interrupting

b. d.

withstand integrated equipment

15. The number “60” in part 3 of the catalog number of an P4 panelboard indicates the panelboard ____________ . a. is 60’’ wide c. is 60” high

b. d.

has 60 circuits is rated for 60 amps

16. The height of an P1 panelboard with 42 circuits is ____________ inches. a. 32 c. 42

80

b. d.

38 44

17.

The height of a 30-pole SE panelboard rated for 125 amps is ____________ inches. a. 44 c. 68

b. d.

50 72

18. The maximum current rating of a P5 panelboard is ____________ amps. a. 1200 c. 100,000

b. d.

600 200,000

19. A P4 panelboard is ____________ inches wide. a. 10 c. 38

b. d.

32 60

20. The line-to-neutral clamping voltage of the Siemens TPS is ____________ volts on a 120/240 1Ø3W system. a. 225 c. 500

b. d.

1000 80,000

81

Notes

82

Notes

83



84

Table of Contents

Introduction ............................................................................. 2 Sensors ................................................................................... 4 Limit Switches ......................................................................... 8 International Limit Switches .................................................. 18 North American Limit Switches ............................................. 22 BERO Sensors ....................................................................... 27 Inductive Proximity Sensors Theory of Operation .................. 28 Inductive Proximity Sensor Family ......................................... 40 Capacitive Proximity Sensors Theory of Operation ................ 54 Capacitive Proximity Sensor Family ....................................... 57 Ultrasonic Proximity Sensors Theory of Operation ................. 59 Ultrasonic Proximity Sensor Family ....................................... 68 Photoelectric Sensors Theory of Operation ............................ 80 Photoelectric Family of Sensors ............................................ 93 Sensor Applications ............................................................... 99 Review Answers .................................................................. 107 Final Exam ........................................................................... 108

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Sensors and related products. Upon completion of Sensors you should be able to:

2

•

Describe advantages, disadvantages, and applications of limit switches, photoelectric sensors, inductive sensors, capacitive sensors, and ultrasonic sensors

•

Describe design and operating principles of mechanical limit switches

•

Identify components of International and North American mechanical limit switches

•

Describe design and operating principles of inductive, capacitive, ultrasonic, and photoelectric sensors and describe differences and similarities

•

Apply correction factors where appropriate to proximity sensors

•

Identify the various scan techniques of photoelectric sensors

•

Identify ten categories of inductive sensors and sensors in each category

•

Describe the effects of dielectric constant on capacitive proximity sensors

•

Identify environmental influences on ultrasonic sensors

•

Identify types of ultrasonic sensors that require manual adjustment, can be used with SONPROG, and require the use of a signal evaluator

•

Describe the difference between light operate and dark operate modes of a photoelectric sensor

•

Describe the use of fiber optics and laser technology used in Siemens photoelectric sensors

•

Select the type of sensor best suited for a particular application based on material, sensing distance, and sensor load requirements

This knowledge will help you better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. You should complete Basics of Electricity and Basics of Control Components before attempting Sensors. An understanding of many of the concepts covered in Basics of Electricity and Basics of Control Components is required for Sensors. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. BERO, SIMATIC, SONPROG, and SIGUARD are registered trademarks of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-1999, National Electrical Code Copyright, 1998, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories, Inc. is a registered trademark of Underwriters Laboratories, Inc., Northbrook, IL 60062. The abbreviation “UL” is understood to mean Underwriters Laboratories, Inc. National Electrical Manufacturers Association is located at 2101 L. Street, N.W., Washington, D.C. 20037. The abbreviation “NEMA” is understood to mean National Electrical Manufacturers Association. Other trademarks are the property of their respective owners. 3

Sensors

One type of feedback frequently needed by industrial-control systems is the position of one or more components of the operation being controlled. Sensors are devices used to provide information on the presence or absence of an object.

Siemens Sensors

4

Siemens sensors include limit switches, photoelectric , inductive, capacitive, and ultrasonic sensors. These products are packaged in various configurations to meet virtually any requirement found in commercial and industrial applications. Each type of sensor will be discussed in detail. At the end of the course an application guide is provided to help determine the right sensor for a given application.

Technologies

Limit switches use a mechanical actuator input, requiring the sensor to change its output when an object is physically touching the switch. Sensors, such as photoelectric, inductive, capacitive, and ultrasonic, change their output when an object is present, but not touching the sensor. In addition to the advantages and disadvantages of each of these sensor types, different sensor technologies are better suited for certain applications. The following table lists the sensor technologies that will be discussed in this course. Sensor

Advantages

Disadvantages

Applications

Limit Switch •High Current Capability •Low Cost •Familiar "LowTech" Sensing

•Requires Physical •Interlocking Contact with •Basic End-ofTarget Travel Sensing •Very Slow Response •Contact Bounce

Photoelectric •Senses all Kinds of Materials •Long Life •Longest Sensing Range •Very Fast Response Time

•Lens Subject to •Packaging Contamination •Material •Sensing Range Handling Affected by Color •Parts Detection and Reflectivity of Target

Inductive

•Resistant to Harsh •Distance Environments Limitations •Very Predictable •Long Life •Easy to Install

Capacitive

•Detects Through Some Containers •Can Detect Non-Metallic Targets

•Very Sensitive to •Level Sensing Extreme Environmental Changes

Ultrasonic

•Senses all Materials

•Resolution •Repeatability •Sensitive to Temperature Changes

•Industrial and Machines •Machine Tool •Senses MetalOnly Targets

•Anti-Collision •Doors •Web Brake •Level Control

5

Contact Arrangement

Contacts are available in several configurations. They may be normally open (NO), normally closed (NC), or a combination of normally open and normally closed contacts. Circuit symbols are used to indicate an open or closed path of current flow. Contacts are shown as normally open (NO) or normally closed (NC). The standard method of showing a contact is by indicating the circuit condition it produces when the contact actuating device is in the deenergized or nonoperated state. For the purpose of explanation in this text a contact or device shown in a state opposite of its normal state will be highlighted. Highlighted symbols used to indicate the opposite state of a contact or device are not legitimate symbols. They are used here for illustrative purposes only.

Mechanical limit switches, which will be covered in the next section, use a different set of symbols. Highlighted symbols are used for illustrative purposes only.

6

Circuit Example

In the following diagram a mechanical limit switch (LS1) has been placed in series with a Run/Stop contact and the “M” contactor coil. The Run/Stop contact is in the Run condition and the motor is running a process. This could be a conveyor or some other device. Note that the “M” contacts and the “Run/ Stop” are shown highlighted, indicating they are normally open contacts in the closed position. LS1 is a normally closed contact of the mechanical limit switch.

When an object makes contact with the mechanical limit switch the LS1 contacts will change state. In this example the normally closed contacts of LS1 open. The mechanical limit switch symbol is highlighted. The “M” contactor coil is deenergized, returning the normally open contacts of the “M” contactor to their normal position, stopping the motor and the process.

7

Limit Switches

A typical limit switch consists of a switch body and an operating head. The switch body includes electrical contacts to energize and deenergize a circuit. The operating head incorporates some type of lever arm or plunger, referred to as an actuator. The standard limit switch is a mechanical device that uses physical contact to detect the presence of an object (target). When the target comes in contact with the actuator, the actuator is rotated from its normal position to the operating position. This mechanical operation activates contacts within the switch body.

8

Principle of Operation

A number of terms must be understood to understand how a mechanical limit switch operates. The free position is the position of the actuator when no external force is applied. Pretravel is the distance or angle traveled in moving the actuator from the free position to the operating position. The operating position is where contacts in the limit switch change from their normal state (NO or NC) to their operated state. Overtravel is the distance the actuator can travel safely beyond the operating point. Differential travel is the distance traveled between the operating position and the release position. The release position is where the contacts change from their operated state to their normal state. Release travel is the distance traveled from the release position to the free position.

9

Momentary Operation

One type of actuator operation is momentary. When the target comes in contact with the actuator, it rotates the actuator from the free position, through the pretravel area, to the operating position. At this point the electrical contacts in the switch body change state. A spring returns the actuator lever and electrical contacts to their free position when the actuator is no longer in contact with the target.

Maintained Operation

In many applications it is desirable to have the actuator lever and electrical contacts remain in their operated state after the actuator is no longer in contact with the target. This is referred to as maintained operation. With maintained operation the actuator lever and contacts return to their free position when a force is applied to the actuator in the opposite direction. A forkstyle actuator is typically used for this application.

10

Snap-Action Contacts

There are two types of contacts, snap-action and slow-break. Snap-action contacts open or close by a snap action regardless of the actuator speed. When force is applied to the actuator in the direction of travel, pressure builds up in the snap spring. When the actuator reaches the operating position of travel, a set of moveable contacts accelerates from its normal position towards a set of fixed contacts. As force is removed from the actuator it returns to its free position. When the actuator reaches the release position the spring mechanism accelerates the moveable contact back to its original state. Since the opening or closing of the contacts is not dependent on the speed of the actuator, snap-action contacts are particularly suited for low actuator speed applications. Snapaction contacts are the most commonly used type of contact.

11

Slow-Break Contacts

Switches with slow-break contacts have moveable contacts that are located in a slide and move directly with the actuator. This ensures the moveable contacts are forced directly by the actuator. Slow-break contacts can either be break-before-make or make-before-break.

In slow-break switches with break-before-make contacts, the normally closed contact opens before the normally open contact closes. This allows the interruption of one function before continuation of another function in a control sequence. In slow-break switches with make-before-break contacts, the normally open contact closes before the normally closed contact opens. This allows the initiation of one function before the interruption of another function.

Contact State Break-Before-Make NO NC Free Position Open Closed Transition Open Open Operated State Closed Open

12

Make-Before-Break NO NC Open Closed Closed Closed Closed Open

Contact Arrangements

There are two basic contact configurations used in limit switches: single-pole, double-throw (SPDT) and double-pole, double-throw (DPDT). This terminology may be confusing if compared to similar terminology for other switch or relay contacts, so it is best just to remember the following points. The single-pole, double-throw contact arrangement consists of one normally open (NO) and one normally closed (NC) contact. The double-pole, double-throw (DPDT) contact arrangement consists of two normally open (NO) and two normally closed (NC) contacts. There are some differences in the symbology used in the North American and International style limit switches. These are illustrated below.

Electrical Ratings

Contacts are rated according to voltage and current. Ratings are generally described as inductive ratings. A typical inductive load is a relay or contactor coil. There are three components to inductive ratings: Make

The load a switch can handle when the mechanical contacts close. This is associated with inrush currents. This is typically two cycles or less.

Break

The load a switch can handle when the mechanical contacts are opened. This is the maximum continuous switch current.

Continuous

The load that a switch can handle without making or breaking a load.

13

The following ratings are typical of Siemens International and North American style limit switches. Inductive AC Contact Ratings

AC Volts 120 240

Inductive DC Contact Ratings

DC Volts 120 240

DC Volts 120 240

Load Connection

14

International and North American Style Make Break Amp VA Amp VA 60 7200 6 720 30 7200 3 720

International Style Make Break Amp VA Amp VA 0.55 69 0.55 69 0.27 69 0.55 69

North American Style Make Break Amp VA Amp VA 0.22 0.22 0.11 0.11 -

Care must be made to ensure that multiple loads on one switch are properly connected. The correct way to wire a switch is so that the loads are connected to the load side of the switch. Loads should never be connected to the line side of the switch.

Actuators

Several types of actuators are available for limit switches, some of which are shown below. There are also variations of actuator types. Actuators shown here are to provide you with a basic knowledge of various types available. The type of actuator selected depends on the application.

Roller Lever

The standard roller is used for most rotary lever applications. It is available in various lengths. When the length of the roller lever is unknown, adjustable length levers are available.

Fork

The fork style actuator must be physically reset after each operation and is ideally suited for transverse movement control.

15

Mounting Considerations

Limit switches should be mounted in locations which will prevent false operations by normal movements of machine components and machine operators. An important aspect of limit switch mounting is cam design. Improper cam design can lead to premature switch failure. For lever arm actuators it is always desirable to have the cam force perpendicular to the lever arm. For applications in which the cam is traveling at speeds less than 100 feet per minute a cam lever angle of 30 degrees is recommended.

Overriding and Non-Overriding Cams

In overriding cam applications it is necessary to angle the trailing edge of the cam in order to prevent the lever arm from snapping back. Snapping back of the lever arm can cause shock loads on the switch which will reduce the life of the switch.

Non-Overriding cams are cams which will not overtravel the actuating mechanism.

16

Flexible Loop and Spring Rod

Flexible loop and spring rod actuators can be actuated from all directions, making them suitable for applications in which the direction of approach is constantly changing.

Plungers

Plunger type actuators are a good choice where short, controlled machine movements are present or where space or mounting does not permit a lever type actuator. The plunger can be activated in the direction of plunger stroke, or at a right angle to its axis.

Mounting Considerations

When using plain and side plunger actuators the cam should be operated in line with the push rod axis. Consideration should be given so as not to exceed the overtravel specifications. In addition, the limit switch should not be used as a mechanical stop for the cam. When using roller top plunger the same considerations should be given as with lever arm actuators.

17

International Limit Switches

International mechanical limit switches are widely used in many countries, including North America. The International Electrotechnical Commission (IEC) and the National Electrical Manufacturers Association (NEMA) develop standards for electrical equipment. Siemens international mechanical switches are built to IEC and NEMA standards. In addition, they are UL listed and CSA certified. International style switches consist of two major components, the operating head and switch body.

International Limit Switch Family

18

A large family of mechanical limit switches is available in the international style to meet virtually any mechanical limit switch application.

Operating Heads

Depending on the switch, Siemens international style limit switches can be fitted with any of several interchangeable operating heads and actuators. Overtravel plunger, roller plunger, roller or angular roller lever, plain or adjustable length roller lever, plain or spring rod, fork lever, or coded sensing heads are available.

The actuator head can be rotated so that the switching direction of limit switches with roller crank, adjustable-length roller crank or rod actuators can operate from any side of the switch body. In addition, roller cranks can be repositioned to the left or right around the operating shaft.

19

Open-Type Limit Switches

Open-type limit switches are intended for use as auxiliary switches in cabinets, large enclosures, or locations where they are not exposed to dust and moisture. A miniature version is available for limited space applications such as automatic door interlocking. Open-type switches use a plunger actuator.

Miniature Formed Housing Limit Switches

Miniature formed housing limit switches are used in applications where space is restricted. The glass-reinforced fiber, flame-retardant molded plastic enclosure resists most shocks, impacts, cutting oils, and penetration from dust and water.

20

Replaceable Contact Block Limit Switches

Siemens has developed two limit switch models with replaceable contact blocks, one with a formed plastic enclosure and one with a metal enclosure. The formed plastic version is in an enclosure similar to the miniature limit switches discussed previously. The metal version is enclosed in die-cast aluminum. It is impervious to most mechanical shocks.

SIGUARD Mechanical Interlock Switches

Sensitivity to safety is an increasing priority for the workplace. Most sensors cannot be used in safety circuits, including proximity sensors and photoelectric sensors which will be covered in later sections. Sensors used in safety circuits must meet stricter design and test standards specified by DIN and IEC. The SIGUARD line of International style switches is designed for safety circuits. SIGUARD mechanical interlock switches have triple coded actuators that act as a key. These devices can be used to control the position of doors, machine guards, gates, and enclosure covers. They can also be used to interrupt operation for user safety. They are available in miniature formed housing and metal housing models.

21

North American Limit Switches

North American mechanical limit switches are specifically designed to meet unique requirements of the North American market. These switches are comprised of three interchangeable components; contact block, switch body, and sensing head. North American limit switches meet UL (Underwriters Laboratory) and CSA (Canadian Standards Association).

Actuators

22

Like the International limit switches, Siemens North American limit switches also accept a variety of operating heads and actuators.

NEMA Type 6P Submersible

The housing for North American NEMA Type 6P submersible limit switch is die-cast metal with an epoxy finish for harsh industrial environments. In addition, the Siemens 6P submersible switch can be used for watertight applications.

Class 54, Rotating Type

Class 54 rotating limit switches are used to limit the travel of electrically operated doors, conveyors, hoists, and similar applications. The contacts are operated when the external shaft is rotated sufficiently. Siemens rotating switches employ a simple reduction worm and gear(s) to provide shaft-to-cam ratios of 18 to 1, 36 to 1, 72 to 1, or 108 to 1. In addition, long dwell cams are available which keeps contacts closed for longer periods of time. This may be necessary in hoist or similar applications. A fine adjustment cam is also available to increase the accuracy of the number of shaft turns required to cause the contacts to operate.

23

Miniature, Prewired, Sealed Switches

Miniature, prewired, sealed switches allow for miniaturization of the electrical connection. The switch is prewired and the terminals and connection are encapsulated in epoxy. The switch uses a single-pole, double-throw contact. The contact can be wired either normally open (NO) or normally closed (NC). Depending on the load voltage, the contact can make up to 7.5 amps and break up to 5 amps.

3SE03 Hazardous Locations, Type EX

Type EX limit switches are designed for extreme environmental service in locations where there exists a danger of an internal or external explosion of flammable gasses, vapors, metal alloy, or grain dust. EX switches are designated by the catalog number 3SE03-EX.

24

Enclosed Basic Switches

North American limit switches are also available in an enclosed basic version. These switches are designated by the catalog number 3SE03-EB. Enclosed basic switches are preconfigured with a plunger actuator, booted plunger, roller lever, booted roller lever, roller plunger, or a booted roller plunger.

25

Review 1 1)

A ____________ ____________ is a type of sensor that requires physical contact with the target.

2)

Which of the following symbols identifies a Normally Closed, Held Open limit switch?

3.

____________ is the distance or angle traveled in moving the actuator from the free position to the operating position.

4.

The ____________ ____________ is where contacts in the limit switch change from their normal state to their operated state.

5.

In slow-break switches with ____________ ____________ - ____________ contacts, the normally closed contact opens before the normally open contact closes.

6.

____________ defines the load a switch can handle when the mechanical contacts are opened. This is the maximum continuous switch current.

7.

For applications in which the cam is travelling at speeds less than 100 feet per minute a cam lever angle of ____________ degrees is recommended.

8.

An International switch consists of an ____________ ____________ and switch body.

9.

____________ is the trade name for a type of International switch suitable for safety circuits.

10. The Siemens ____________ submersible switch can be used for watertight applications.

26

BERO Sensors

BERO is the trade name used by Siemens to identify its line of “no-touch” sensors. Siemens BERO sensors operate with no mechanical contact or wear. In the following application, for example, a BERO sensor is used to determine if cans are in the right position on a conveyor.

Types of BERO Sensors

There are four types of BERO sensors: inductive, capacitive, ultrasonic, and photoelectric. Inductive proximity sensors use an electromagnetic field to detect the presence of metal objects. Capacitive proximity sensors use an electrostatic field to detect the presence of any object. Ultrasonic proximity sensors use sound waves to detect the presence of objects. Photoelectric sensors react on changes in the received quantity of light. Some photoelectric sensors can even detect a specific color.

Sensor

Objects Detected

Technology

Inductive Capacitive Ultrasonic

Metal Any Any

Electromagnetic Field Electrostatic Field Sound Waves

Photoelectric

Any

Light

27

Inductive Proximity Sensors Theory of Operation

In this section we will look at BERO inductive proximity sensors, and how they detect the presence of an object without coming into physical contact with it. Inductive proximity sensors are available in a variety of sizes and configurations to meet varying applications. Specific sensors will be covered in more detailed in the following section.

Electromagnetic Coil and Metal Target

28

The sensor incorporates an electromagnetic coil which is used to detect the presence of a conductive metal object. The sensor will ignore the presence of an object if it is not metal.

ECKO

Siemens BERO inductive proximity sensors are operated using an Eddy Current Killed Oscillator (ECKO) principle. This type of sensor consists of four elements: coil, oscillator, trigger circuit, and an output. The oscillator is an inductive capacitive tuned circuit that creates a radio frequency. The electromagnetic field produced by the oscillator is emitted from the coil away from the face of the sensor. The circuit has just enough feedback from the field to keep the oscillator going.

When a metal target enters the field, eddy currents circulate within the target. This causes a load on the sensor, decreasing the amplitude of the electromagnetic field. As the target approaches the sensor the eddy currents increase, increasing the load on the oscillator and further decreasing the amplitude of the field. The trigger circuit monitors the oscillator’s amplitude and at a predetermined level switches the output state of the sensor from its normal condition (on or off). As the target moves away from the sensor, the oscillator’s amplitude increases. At a predetermined level the trigger switches the output state of the sensor back to its normal condition (on or off).

29

Operating Voltages

Siemens inductive proximity sensors include AC, DC, and AC/ DC (universal voltage) models. The basic operating voltage ranges are from 10 to 30 VDC, 15 to 34 VDC, 10 to 65 VDC, 20 to 320 VDC, and 20 to 265 VAC.

Direct Current Devices

Direct current models are typically three-wire devices (two-wire also available) requiring a separate power supply. The sensor is connected between the positive and negative sides of the power supply. The load is connected between the sensor and one side of the power supply. The specific polarity of the connection depends on the sensor model. In the following example the load is connected between the negative side of the power supply and the sensor.

Output Configurations

Three-wire, DC proximity sensor can either be PNP (sourcing) or NPN (sinking). This refers to the type of transistor used in the output switching of the transistor. The following drawing illustrates the output stage of a PNP sensor. The load is connected between the output (A) and the negative side of the power supply (L-). A PNP transistor switches the load to the positive side of the power supply (L+). When the transistor switches on, a complete path of current flow exists from L- through the load to L+. This is also referred to as current sourcing since in this configuration conventional current is (+ to -) sourced to the load. This terminology is often confusing to new users of sensors since electron current flow (to +) is from the load into the sensor when the PNP transistor turns on.

30

The following drawing illustrates the output of an NPN sensor. The load is connected between the output (A) and the positive side of the power supply (L+). An NPN transistor switches the load to the negative side of the power supply (L-). This is also referred to as current sinking since the direction of conventional current is into the sensor when the transistor turns on. Again, the flow of electron current is in the opposite direction.

Normally Open (NO) Normally Closed (NC)

Outputs are considered normally open (NO) or normally closed (NC) based on the condition of the transistor when a target is absent. If, for example, the PNP output is off when the target is absent then it is a normally open device. If the PNP output is on when the target is absent it is a normally closed device.

Complementary

Transistor devices can also be complementary (four-wire). A complementary output is defined as having both normally open and normally closed contacts in the same sensor.

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Series and Parallel Connections

In some applications it may be desirable to use more than one sensor to control a process. Sensors can be connected in series or in parallel. When sensors are connected in series all the sensors must be on to turn on the output. When sensors are connected in parallel either sensor will turn the output on. There are some limitations that must be considered when connecting sensors in series. In particular, the required supply voltage increases with the number of devices placed in series.

Shielding

32

Proximity sensors contain coils that are wound in ferrite cores. They can be shielded or unshielded. Unshielded sensors usually have a greater sensing distance than shielded sensors.

Shielded Proximity Sensors

The ferrite core concentrates the radiated field in the direction of use. A shielded proximity sensor has a metal ring placed around the core to restrict the lateral radiation of the field. Shielded proximity sensors can be flush mounted in metal. A metal-free space is recommended above and around the sensor’s sensing surface. Refer to the sensor catalog for this specification. If there is a metal surface opposite the proximity sensor it must be at least three times the rated sensing distance of the sensor from the sensing surface.

Unshielded Proximity Sensors

An unshielded proximity sensor does not have a metal ring around the core to restrict lateral radiation of the field. Unshielded sensors cannot be flush mounted in metal. There must be an area around the sensing surface that is metal free. An area of at least three times the diameter of the sensing surface must be cleared around the sensing surface of the sensor. In addition, the sensor must be mounted so that the metal surface of the mounting area is at least two times the sensing distance from the sensing face. If there is a metal surface opposite of the proximity sensor it must be at least three times the rated sensing distance of the sensor from the sensing surface.

33

Mounting Multiple Sensors

Care must be taken when using multiple sensors. When two or more sensors are mounted adjacent to or opposite one another, interference or cross-talk can occur producing false outputs. The following guidelines can generally be used to minimize interference. •

Opposite shielded sensors should be separated by at least four times the rated sensing range

•

Opposite unshielded sensors should be separated by at least six times the rated sensing range

•

Adjacent shielded sensors should be separated by at least two times the diameter of the sensor face

•

Adjacent unshielded sensors should be separated by at least three times the diameter of the sensor face

These are general guidelines. BERO proximity sensors have individual specifications which should be followed. For instance, some devices are rated as suitable for side-by-side mounting.

34

Standard Target

A standard target is defined as having a flat, smooth surface, made of mild steel that is 1 mm (0.04”) thick. Steel is available in various grades. Mild steel is composed of a higher content of iron and carbon. The standard target used with shielded sensors has sides equal to the diameter of the sensing face. The standard target used with unshielded sensors has sides equal to the diameter of the sensing face or three times the rated operating range,whichever is greater. If the target is larger than the standard target, the sensing range does not change. However, if the target is smaller or irregular shaped the sensing distance (Sn) decreases. The smaller the area of the target the closer it must be to the sensing face to be detected.

Target Size Correction Factor

A correction factor can be applied when targets are smaller than the standard target. To determine the sensing distance for a target that is smaller than the standard target (Snew), multiply the rated sensing distance (Srated) times the correction factor (T). If, for example, a shielded sensor has a rated sensing distance of 1 mm and the target is half the size of the standard target, the new sensing distance is 0.83 mm (1 mm x 0.83). Snew = Srated x T Snew = 1 mm x 0.83 Snew = 0.83 mm Size of Target Compared to Standard Target 25% 50% 75% 100%

Correction Factor Shielded Unshielded 0.56 0.50 0.83 0.73 0.92 0.90 1.00 1.00

35

Target Thickness

Thickness of the target is another factor that should be considered. The sensing distance is constant for the standard target. However, for nonferrous targets such as brass, aluminum, and copper a phenomenon known as “skin effect” occurs. Sensing distance decreases as the target thickness increases. If the target is other than the standard target a correction factor must be applied for the thickness of the target.

Target Material

The target material also has an effect on the sensing distance. When the material is other than mild steel correction factors need to be applied.

Material Mild Steel, Carbon Aluminum Foil 300 Series Stainless Steel Brass Aluminum Copper

36

Correction Factor Shielded Unshielded 1.00 1.00 0.90 1.00 0.70 0.08 0.40 0.50 0.35 0.45 0.30 0.40

Rated Operating Distances

The rated sensing distance (Sn) is a theoretical value which does not take into account such things as manufacturing tolerances, operating temperature, and supply voltage. In some applications the sensor may recognize a target that is outside of the rated sensing distance. In other applications the target may not be recognized until it is closer than the rated sensing distance. Several other terms must be considered when evaluating an application. The effective operating distance (Sr) is measured at nominal supply voltage at an ambient temperature of 23°C ± 0.5°. It takes into account manufacturing tolerances. The effective operating distance is ±10% of the rated operating distance. This means the target will be sensed between 0 and 90% of the rated sensing distance. Depending on the device, however, the effective sensing distance can be as far out as 110% of the rated sensing distance. The useful switching distance (Su) is the switching distance measured under specified temperature and voltage conditions. The useful switching distance is ±10% of the effective operating distance. The guaranteed operating distance (Sa) is any switching distance for which an operation of the proximity switch within specific permissible operating conditions is guaranteed. The guaranteed operating distance is between 0 and 81% of the rated operating distance.

37

Response Characteristic

Proximity switches respond to an object only when it is in a defined area in front of the switch’s sensing face. The point at which the proximity switch recognizes an incoming target is the operating point. The point at which an outgoing target causes the device to switch back to its normal state is called the release point. The area between these two points is called the hysteresis zone.

Response Curve

The size and shape of the response curve depends on the specific proximity switch. The following curve represents one type of proximity switch.

38

Review 2 1)

An ____________ sensor uses an electromagnetic field and can only detect metal objects.

2)

Which of the following is not an element of an inductive proximity sensor. a. Target b. Electrical Coil c. Oscillator d. Trigger Circuit e. Output

3)

An area surrounding an unshielded inductive proximity sensor of at least ____________ times the area of the sensing face must be metal free.

4)

Shielded inductive proximity sensors mounted opposite each other should be mounted at least ____________ times the rated sensing area from each other.

5)

A standard target for an inductive proximity sensor is made of mild ____________ and is 1 mm thick.

6)

A correction factor of ____________ should be applied to a shielded inductive proximity sensor when the target is made of brass.

7)

The guaranteed operating distance of an inductive proximity switch is between 0 and ____________ % of the rated operating distance.

39

Inductive Proximity Sensor Family

In this section we will look at the 3RG4 and 3RG04 families of inductive proximity sensors. 3RG4 refers to the first part of the part number that is used to identify this line of sensors.

40

Categories

Inductive proximity sensors are available in ten categories. Each category will be briefly discussed and followed by a selection guide.

Normal Requirements Cylindrical

Inductive proximity sensors designed for normal requirements are also referred to as the standard series. These sensors will meet the needs of normal or standard applications. Standard series sensors used for normal requirements are available in several sizes, including the shorty version which is used where mounting space is limited. The diameter sensing face ranges from 3 mm to 34 mm. In addition, standard series sensors come with PNP or NPN outputs in 2, 3, or 4 wires. Standard series sensors can handle loads up to 200 mA.

41

Normal Requirements Cylindrical Selection Guide

The following Inductive Proximity Selection Guide will help you find the right sensor for a given application. The housing dimension column refers to the diameter of the sensing face. The material column identifies if the sensor body is made of stainless steel (SST), brass, or a molded plastic.

Housing Shielded Operating Dimension Material Sn (mm) Wires Unshielded Voltage (mm) 3, 4 5 6.5

8

12

18

20 30

34

42

SST Brass SST SST SST SST SST Brass SST SST SST Brass SST SST Brass Brass SST SST Brass Brass SST SST SST Brass Brass SST SST Brass Plastic Brass Brass SST SST Brass Brass SST SST Brass Plastic

Shielded Shielded Shielded Shielded Unshielded Shielded Shielded Shielded Shielded Shielded Unshielded Shielded Shielded Shielded Shielded Unshielded Unshielded Unshielded Unshielded Shielded Shielded Shielded Shielded Shielded Unshielded Unshielded Unshielded Unshielded Unshielded Shielded Shielded Shielded Shielded Shielded Unshielded Unshielded Unshielded Unshielded Unshielded

0.6-0.8 0.8 1.5 1.5 2.5 1 1 1.5 1.5 1.5 2.5 2 2 2 2 4 4 4 4 5 5 5 5 5 8 8 8 8 10 10 10 10 10 10 15 15 15 15 20

10-30 VDC 10-30 VDC 15-34 VDC 10-30 VDC 15-34 VDC 15-34 VDC 10-30 VDC 10-30 VDC 15-34 VDC 10-30 VDC 15-34 VDC 15-34 VDC 10-55 VDC 20-250 VAC 20-250 VAC 15-34 VDC 10-55 VDC 20-250 VAC 20-250 VAC 15-34 VDC 10-30 VDC 10-55 VDC 20-250 VAC 20-250 VAC 15-34 VDC 10-55 VDC 20-250 VAC 20-250 VAC 10-36 VDC 15-34 VDC 10-30 VDC 10-55 VDC 20-250 VAC 20-250 VAC 15-34 VDC 10-55 VDC 20-250 VAC 20-250 VAC 10-36 VDC

3 3 3 3 3 3 4 3 3 3, 4 3 3, 4 2 2 2 3, 4 2 2 2 3, 4 4 2 2 2 3,4 2 2 2 3 3, 4 4 2 2 2 3, 4 2 2 2 3

Normal Requirements Cubic Shape

Inductive proximity sensors designed for normal requirements are also available in a block or cubic shape.

Normal Requirements Cubic Shape Selection Guide

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 5x5 8x8 18 Tubular (Flat Pack) 40x26x12 26x40x12

Optimized for Solid State Inputs

Wires

Brass Brass Plastic

Shielded Shielded Shielded

0.8 1.5 4

10-30 VDC 10-30 VDC 10-30 VDC

3 3 3

Plastic Plastic

Shielded Shielded Unshielded Shielded Shielded Unshielded Shielded Unshielded

2 2 4 2 2.5 5 15 20

15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC

3, 4 3 3 4 3, 4 3, 4 4 4

Shielded Unshielded Shielded Unshielded Shielded Unshielded Unshielded

35 35 35 35 25 30 40

15-34 VDC 15-34 VDC 20-265 VAC 20-265 VAC 15-34 VDC 15-34 VDC 15-34 VDC

4 4 2 2 4 4 4

40x32x12.5 Block with M14 40x40 (Limit Switch Style)

Plastic Plastic Plastic Plastic Plastic

40x40x40

Plastic

40x40x40

Plastic

40x60 (Flat Pack) 40x80 (Flat Pack)

Plastic Plastic Plastic

These two-wire devices are optimized for use with solid state inputs such as PLCs and solid state timing relays. Optimized for solid state input sensors are available in tubular (shown) and block packs (not shown).

43

Optimized for Solid State Inputs Selection Guide

Housing Shielded Operating Dimension Material Sn (mm) Wires Unshielded Voltage (mm) 8 12 18 30 Block with M14 40x40 (Limit Switch Style)

Extra Duty

44

SST Brass Brass Brass Brass Brass Brass Plastic

Shielded Shielded Unshielded Shielded Unshielded Shielded Unshielded Shielded

1 2 4 5 8 10 15 2.5

15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC

2 2 2 2 2 2 2 2

Plastic Plastic

Shielded Unshielded

15 20

15-34 VDC 15-34 VDC

2 2

Some applications require a higher operating voltage, or a faster switching frequency than is found with standard series sensors. This group of inductive proximity sensors provides a higher operating range and can handle loads up to 300 mA. These are two-wire and three-wire devices available in either normally open (NO) or normally closed (NC) configurations. They are available in cylindrical or cubic shape.

Extra Duty Selection Guide

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 8 12

SST Brass

Shielded Shielded

1 2

Brass Brass

Shielded Unshielded

2 4

Brass Brass

Unshielded Shielded

4 10

Brass Brass

Shielded Unshielded

20

Brass Plastic

Unshielded Unshielded

10

30

Brass

Shielded

10

Brass Brass

Shielded Unshielded

10 15

Brass

Unshielded

15

34

Plastic

Unshielded

20

20-265 VAC/ 20-320 VDC

2

Block with M14

Plastic

Shielded

2.5

2


Shielded Unshielded Shielded

2.5 5 15

Plastic Plastic

Shielded Unshielded

15 20

Plastic Plastic

Unshielded Unshielded

20 30

Plastic Plastic

Unshielded Shielded

30 30

Plastic

Unshielded

40

Plastic

Unshielded

40

Plastic

Unshielded

40

20-265 VAC/ 20-320 VDC 10-65VDC 10-65 VDC 20-265 VAC/ 20-320 VDC 10-65 VDC 20-265 VAC/ 20-320 VDC 10-65 VDC 20-265 VAC/ 20-320 VDC 10-65 VDC 20-265 VAC/ 20-320 VDC 20-265 VAC/ 20-320 VDC 20-265 VAC/ 20-320 VDC 10-65 VDC

18

40x40 (Limit Switch Style)

40x60 (Flat Pack) 40x80 (Flat Pack)

10-65 VDC 20-265 VAC/ 20-320 VDC 10-65 VDC 20-265 VAC/ 20-320 VDC 10-65VDC 20-265 VAC/ 20-320 VDC 10-65 VDC 20-265 VAC/ 20-320 VDC 10-65VDC 20-265 VAC/ 20-320 VDC 20-265 VAC/ 20-320 VDC 10-65 VDC 20-265 VAC/ 20-320 VDC 10-65VDC

Wires 3 2 3 2 3 2 3 2 3 2 2 3 2 3

3 3 2 3

2 3 2 2 2 3

45

Extreme Environmental Conditions (IP68)

Extreme Environmental Conditions (IP68) Selection Guide

IP protection is a European system of classification which indicates the degree of protection an enclosure provides against dust, liquids, solid objects, and personnel contact. The IP system of classification is accepted internationally. Proximity switches classified IP68 provide protection against the penetration of dust, complete protection against electrical shock, and protection against ingress of water on continuous submersion. These are three- and four-wire devices configured for NPN or PNP, normally closed (NC) or normally open (NO) outputs.

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 4.5 6.5 8 12

18

30

40x40 (Limit Switch Style)

46

SST Brass Brass Plastic Brass Plastic Brass Plastic Brass Plastic Brass Plastic

Shielded Unshielded Unshielded Shielded Shielded Unshielded Unshielded Shielded Shielded Unshielded Unshielded Unshielded

0.6 2.5 2.5 2 2 4 4 5 5 8 8 8

Plastic Plastic Brass Plastic Brass Plastic

Unshielded Shielded Shielded Unshielded Unshielded Unshielded

8 10 10 15 15 15

Plastic Plastic

Unshielded Shielded

15 15

10-30 VDC 10-30 VDC 10-30 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 20-265 VAC 20-250 VDC 10-65 VDC 15-34 VDC 15-34 VDC 15-34 VDC 15-34 VDC 20-265 VAC 20-250 VDC 10-65 VDC 15-34 VDC

Wires 3 3 3 3 3 3 3 3 3 3 3 2 3 3 3 3 3 2 3 4

Greater Rated Operating Sensing Range

These devices provide a greater operating distance in comparison with standard proximity switches. Devices are three-wire DC with PNP or NPN or AC and normally open (NO) or normally closed (NC) output configurations.

Greater Rated Operating Sensing Range Selection Guide

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 6.5 8

12

18

30

8x8 40x40 (Limit Switch Style) 40x40 (Mini Base) 40x60 (Flat Pack) 40x80 (Flat Pack)

Wires

Brass SST Brass Brass Brass Brass Brass Plastic Brass Brass Brass Brass Brass Brass Plastic Plastic Plastic Plastic Plastic

Unshielded 3 10-30 VDC Shielded 2 15-34 VDC Unshielded 3 10-30 VDC Unshielded 6 10-30 VDC Shielded 4 15-34 VDC Shielded 6 10-30 VDC Unshielded 10 10-30 VDC Shielded 8 15-34 VDC Unshielded 12 10-30 VDC Unshielded 20 10-30 VDC Shielded 15 15-34 VDC Shielded 22 10-30 VDC Unshielded 40 10-30 VDC Unshielded 3 10-30 VDC Shielded 20 15-34 VDC Unshielded 25 10-65 VDC Unshielded 40/25(adj) 10-65 VDC Unshielded 40 10-65 VDC Shielded 20 10-30 VDC

3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

Plastic

Unshielded

50

10-65 VDC

3

Plastic

Unshielded

65

10-65 VDC

3

47

NAMUR

NAMUR is a standard issued by the Standards Committee of Measurement and Control of the chemical industry in Europe. Deutsche Industrie Normenausschuss (DIN) refers to a set of German standards now used in many countries. Like NAMUR, DIN 19234 is a set of standards for equipment used in hazardous locations.

Intrinsically Safe

NAMUR sensors are intrinsically safe only when used with an approved barrier power supply/output device and approved cabling. It is beyond the scope of this course to offer a complete explanation on this subject. You are encouraged to become familiar with Articles 500 through 504 of the National Electrical Code® which cover the use of electrical equipment in locations where fire or explosions due to gas, flammable liquids, combustible dust, or ignitable fibers may be possible.

Divisions

Division I identifies a condition where hazardous materials are normally present in the atmosphere. Division II identifies conditions where an atmosphere may become hazardous as result of abnormal conditions. This may occur if, for example, a pipe containing a hazardous chemical begins to leak.

Classes and Groups

Hazardous locations are further defined by class and group. Class I, Groups A through D are chemical gases or liquids. Class II, Groups E, F, and G include flammable dust. Class III is not divided into groups. It includes all ignitable fibers and lints such as clothing fiber in textile mills.

A B C

D

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Group

Class I Groups A-D Gases and Liquids Acetylene E Hydrogen F Acetaldehyde G Ethylene Methyl Ether Acetone Gasoline Methanol Propane

Class II Groups E-G Flammable Dust Metallic Dust Carbon Dust Grain Dust

Group

Although you should never specify or suggest the type of location, it is important to understand regulations that apply to hazardous locations. It is the user’s responsibility to contact local regulatory agencies to define the location as Division I or II and to comply with all applicable codes.

Group

Hazardous Environments

Class III Ignitable Fibers Rayon Jute

NAMUR Selection Guide

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 4.5 8 12 18 30 40x40 (Limit Switch Style)

Pressure Proof

Pressure Proof Selection Guide

SST SST SST SST SST SST SST SST Plastic

Shielded Shielded Shielded Unshielded Shielded Unshielded Shielded Unshielded Shielded

0.8 1.5 2 4 5 8 10 15 15

5-25 VDC 5-25 VDC 5-25 VDC 5-25 VDC 5-25 VDC 5-25 VDC 5-25 VDC 5-25 VDC 5-25 VDC

Wires 2 2 2 2 2 2 2 2 2

These devices are used in extremely dynamic pressure stressing such as the monitoring of piston or valve limit positions, speed monitoring and measurement of hydraulic motors, and vacuum applications. The operating voltage is 10 to 30 VDC, with loads up to 200 mA. The operating distance of devices rated up to 7253 psi is 3 mm. These are three-wire devices with a PNP or NPN, normally open (NO) or normally closed (NC) output.

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 12

SST

Unshielded

3

10-30 VDC

Wires 3

49

UBERO Without Reduction Factor/Weld Field Immune

UBERO Without Reduction Factor/Weld Field Immune Selection Guide

Standard BERO proximity switches require a reduction factor for metals other than the standard target. UBERO products sense all metals without a reduction factor. They can also be used in applications near a strong magnetic fields.

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 8 12 18 30 40x40 (Limit Switch Style) 40x40 (Mini Base) 80x80

50

Wires

Shielded Unshielded Brass or Shielded Unshielded SST Brass or Shielded Unshielded SST Brass or Shielded Unshielded SST Plastic Shielded Plastic Unshielded Plastic Unshielded

1.5 4 2 8 5 12 10 20 15 25 40

10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC

3 3 3 3 3 3 3 3 4 3 4

Plastic Plastic Plastic Plastic

15 25 35 75

10-30 VDC 10-30 VDC 10-30 VDC 10-30 VDC

3 3 3 4

SST

Shielded Unshielded Unshielded Unshielded

AS-i

Actuator Sensor Interface (AS-i or AS-Interface) is a system for networking binary devices such as sensors. Until recently, extensive parallel control wiring was needed to connect sensors to the controlling device. PLCs, for example, use I/O modules to receive inputs from binary devices such as sensors. Binary outputs are used to turn on or off a process as the result of an input. Using conventional wiring it would take a cable harness of several parallel inputs to accomplish complex tasks.

AS-i replaces the complex cable harness with a simple 2-core cable. The cable is designed so that devices can only be connected correctly.

Inductive proximity sensors developed for use on AS-i have the AS-i chip and intelligence built into the device

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AS-i Selection Guide

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 12 18 20 30 34 40x40

Analog Output

Analog Selection Guide

Shielded Shielded Unshielded Shielded Unshielded Shielded

2 5 10 10 20 15

20-32 VDC 20-32 VDC 20-32 VDC 20-32 VDC 20-32 VDC 20-32 VDC

These devices are used when an analog value is required. In some applications it may be desireable to know the distance a target is from the sensor. The rated sensing range of an inductive analog sensor is 0 to 6 mm. The output of the sensor increases from 1 to 5 VDC or 0 to 5 mA as the target is moved away from the sensor.

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 12

52

Brass Brass Plastic Brass Plastic Plastic

Brass

Unshielded

0-6

10-30 VDC

Wires 4

Review 3 1)

Inductive proximity sensors are divided into ____________ categories.

2)

The maximum sensing range of an inductive proximity sensor with a cylindrical style housing in the standard series (normal requirements) is ____________ mm.

3)

The maximum operating voltage that can be used on an inductive proximity sensor for increased electric requirements is ____________ VAC or ____________ VDC.

4)

____________ is a European system of classification which indicates the degree of protection an enclosure provides against dust, liquids, solid objects, and personnel contact.

5)

The maximum sensing range of an inductive proximity sensor designated for greater rated distance is ____________ mm.

6)

____________ inductive proximity sensors detect all metals without a reduction factor.

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Capacitive Proximity Sensors Theory of Operation

Capacitive proximity sensors are similar to inductive proximity sensors. The main difference between the two types is that capacitive proximity sensors produce an electrostatic field instead of an electromagnetic field. Capacitive proximity switches will sense metal as well as nonmetallic materials such as paper, glass, liquids, and cloth.

The sensing surface of a capacitive sensor is formed by two concentrically shaped metal electrodes of an unwound capacitor. When an object nears the sensing surface it enters the electrostatic field of the electrodes and changes the capacitance in an oscillator circuit. As a result, the oscillator begins oscillating. The trigger circuit reads the oscillator’s amplitude and when it reaches a specific level the output state of the sensor changes. As the target moves away from the sensor the oscillator’s amplitude decreases, switching the sensor output back to its original state.

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Standard Target and Dielectric Constant

Standard targets are specified for each capacitive sensor. The standard target is usually defined as metal and/or water. Capacitive sensors depend on the dielectric constant of the target. The larger the dielectric number of a material the easier it is to detect. The following graph shows the relationship of the dielectric constant of a target and the sensor’s ability to detect the material based on the rated sensing distance (Sr).

The following table shows the dielectric constants of some materials. If, for example, a capacitive sensor has a rated sensing distance of 10 mm and the target is alcohol, the effective sensing distance (Sr) is approximately 85% of the rated distance, or 8.5 mm. Material Alcohol Araldite Bakelite Glass Mica Hard Rubber Paper-Based Laminate Wood Cable Casting Compound Air, Vacuum Marble Oil-Impregnated Paper Paper Paraffin Petroleum Plexiglas

Dielectric Constant

Material

Dielectric Constant

25.8 3.6 3.6 5 6 4 4.5 2.7 2.5 1 8 4 2.3 2.2 2.2 3.2

Polyamide Polyethylene Polyproplene Polystyrene Polyvinyl Chloride Porcelain Pressboard Silica Glass Silica Sand Silicone Rubber Teflon Turpentine Oil Transformer Oil Water Soft Rubber Celluloid

5 2.3 2.3 3 2.9 4.4 4 3.7 4.5 2.8 2 2.2 2.2 80 2.5 3

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Detection Through Barriers

One application for capacitive proximity sensors is level detection through a barrier. For example, water has a much higher dielectric than plastic. This gives the sensor the ability to “see through” the plastic and detect the water.

Shielding

All Siemens capacitive sensors are shielded. These sensors will detect conductive material such as copper, aluminum, or conductive fluids, and nonconductive material such as glass, plastic, cloth, and paper. Shielded sensors can be flush mounted without adversely affecting their sensing characteristics. Care must be taken to ensure that this type of sensor is used in a dry environment. Liquid on the sensing surface could cause the sensor to operate.

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Capacitive Proximity Sensor Family

The 3RG16 product family identifies the Siemens capacitive proximity sensor. Units are available in DC or AC versions. Electronic controls such as SIMATIC® PLCs or relays can be controlled directly with the DC voltage version. In the case of the AC voltage version the load (contactor relay, solenoid valve) is connected with the sensor in series directly to the AC voltage. Sensors are available with two-, three-, and four-wire outputs.

Capacitive Sensor Selection Guide

Housing Shielded Operating Dimension Material Sn (mm) Unshielded Voltage (mm) 18 30

40 40x40 (Limit Switch Style) 20x20 (Flat Pack)

Wires

Plastic Metal Plastic Metal Plastic Plastic Plastic Plastic Plastic

Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded

5 10 10 10 10 20 20 20 20

10-65 VDC 20-250 VAC 20-250 VAC 10-65 VDC 10-65 VDC 20-250 VAC 10-65 VDC 20-250 VAC 10-65 VDC

3 3 2 4 4 2 4 2 4

Metal

Shielded

5

10-30 VDC

3

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Review 4 1)

A main difference between an inductive proximity sensor and a capacitive proximity sensor is that a capacitive proximity sensor produces an ____________ field.

2)

Capacitive proximity sensors will sense ____________ material.

3)

The larger the ____________ constant of a material the easier it is for a capacitive proximity sense to detect.

4)

It is easier for a capacitive proximity sensor to detect ____________ than porcelain. a. teflon b. marble c. petroleum d. paper

5)

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The maximum rated sensing distance of a capacitive proximity sensor is ____________ mm.

Ultrasonic Proximity Sensors Theory of Operation

Ultrasonic proximity sensors use a transducer to send and receive high frequency sound signals. When a target enters the beam the sound is reflected back to the switch, causing it to energize or deenergize the output circuit.

Piezoelectric Disk

A piezoelectric ceramic disk is mounted in the sensor surface. It can transmit and receive high-frequency pulses. A highfrequency voltage is applied to the disk, causing it to vibrate at the same frequency. The vibrating disk produces high-frequency sound waves. When transmitted pulses strike a sound-reflecting object, echoes are produced. The duration of the reflected pulse is evaluated at the transducer. When the target enters the preset operating range, the output of the switch changes state. When the target leaves the preset operating range, the output returns to its original state.

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The emitted pulse is actually a set of 30 pulses at an amplitude of 200 Kvolts. The echo can be in microvolts.

Blind Zone

A blind zone exists directly in front of the sensor. Depending on the sensor the blind zone is from 6 to 80 cm. An object placed in the blind zone will produce an unstable output.

Range Definition

The time interval between the transmitted signal and the echo is directly proportional to the distance between the object and sensor. The operating range can be adjusted in terms of its width and position within the sensing range. The upper limit can be adjusted on all sensors. The lower limit can be adjusted only with certain versions. Objects beyond the upper limit do not produce a change at the output of the sensor. This is known as “blanking out the background” . On some sensors, a blocking range also exists. This is between the lower limit and the blind zone. An object in the blocking range prevents identification of a target in the operating range. There is a signal output assigned to both the operating range and the output range.

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The radiation pattern of an ultrasonic sensor consists of a main cone and several neighboring cones. The approximate angle of the main cone is 5°.

Free Zones

Free zones must be maintained around the sensor to allow for neighboring cones. The following examples show the free area required for different situations.

Parallel Sensors

In the first example, two sonar sensors with the same sensing range have been mounted parallel to each other. The targets are vertical to the sound cone. The distance between the sensors is determined by the sensing range. For example, if the sensing range of the sensors is 6 cm, they must be located at least 15 cm apart.

Target

Radiation Pattern

Target

X

Sensing Range (CM) 6-30 20-130 40-300 60-600 80-1000

X (CM) >15 >60 >150 >250 >350

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Mutual Interference

Mutual interference occurs when sonar devices are mounted in close proximity to each other and the target is in a position to reflect echoes back to a sensor in the proximity of the transmitting sensor. In this case, the distance between sensors (X) can be determined through experimentation.

Opposing Sensors

In the following example, two sonar sensors with the same sensing range have been positioned opposite of each other. A minimum distance (X) is required between opposing sensors so that mutual interferance does not occur.

X

X Sensing Range (CM) (CM) 6-30 >120 20-130 >400 40-300 >1200 60-600 >2500 80-1000 >4000

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Flat and Irregular Shaped Surfaces

Sonar sensors mounted next to a flat surface, such as a wall or smooth machine face, require less free area than sensors mounted next to an irregular shaped surface.

Sensing Range (CM) 6-130 20-130 40-300 60-600 80-1000

Angular Alignment

X (CM)

Y (CM)

>3 >15 >30 >40 >70

>6 >30 >60 >80 >150

The angle of the target entering the sound cone must also be considered. The maximum deviation from the send direction to a flat surface is ±3°.

If the angle were greater than 3° the sonic pulses would be reflected away and the sensor would not receive an echo.

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Liquids and Coarse-Grained Materials

Liquids, such as water, are also limited to an angular alignment of 3°. Coarse-grained materials, such as sand, can have an angular deviation as much as 45°. This is because the sound is reflected over a larger angle by coarse-grained materials.

Blanking Out Objects

An object may be located in the vicinity of the sound cone that causes improper operating of the sensor. These objects can be blanked out by using an aperture made of a sound absorbing material such as rock wool. This narrows the sound cone and prevents pulses from reaching the interfering object.

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Operating Modes

Sonar sensors can be setup to operate in several different modes: diffuse, reflex, and thru-beam.

Diffuse Mode

This is the standard mode of operation. Objects, traveling in any direction into the operating range of the sound cone, will cause the sensor output to switch states. This mode of operation is similar to a proximity sensor.

Reflex Mode

The reflex mode uses a reflector located in the preset operating range. The operating range is adjusted for the reflector. The pulses are bounced off the reflector and the echo pulses are returned to the sensor. When a target blocks the echo pulses the output is activated. Typically used in applications where the target is not a good sound absorber.

Thru-Beam Mode

Thru-beam sensors consist of a transmitter, which emits ultrasonic pulses, and a receiver. If the beam between the transmitter and the receiver is interrupted the output of the receiver switches state.

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Environmental Influences

Sound travel time can be affected by physical properties of the air. This, in turn, can affect the preset operating distance of the sensor. Condition Temperature Pressure

Vacuum Humidity

Air Currents

Gas

Precipitation

Paint Mist Dust

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Effect Sonic wave speed changes by 0.17%/°K. Most sensors have a compensation adjustment. With normal atmospheric variation of ±5%, sound velocity varies approximately ±0.6%. Sound velocity decreases 3.6% between sea level and 3 km above sea level. Adjust sensor for appropriate operating range. Sensors will not operate in a vacuum. Sound velocity increases as humidity increases. This leads to the impression of a shorter distance to the target. The increase of velocity from dry to moisturesaturated air is up to 2%. Wind Speed 100 km/h - No Echo Received by Sensor Sensors are designed for operation in normal atmospheric conditions. If sensors are operated in other types of atmospheres, such as carbon dioxide, measuring errors will occur. Rain or snow of normal density does not impair the operation of a sensor. The transducer surface should be kept dry. Paint mist in the air will have no effect, however, paint mist should not be allowed to settle on transducer surface. Dusty environments can lower sensing range 25-33%.

Review 5 1)

Ultrasonic proximity sensors use high frequency ____________ signals to detect the presence of a target.

2)

The blind zone of an ultrasonic proximity sensor can be from ____________ - ____________ cm, depending on the sensor.

3)

The approximate angle of the main sound cone of an ultrasonic proximity sensor is ____________ degrees.

4)

The free zone between two parallel ultrasonic sensors with a rated sensing range of 20-130 cm must be greater than ____________ cm.

5)

The maximum angle of deviation from the send direction of an ultrasonic sensor to a flat surface is ____________ degrees.

6)

____________ mode is the standard mode of operation for an ultrasonic sensor.

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Ultrasonic Proximity Sensor Family

The ultrasonic proximity sensor family consists of a Thru-Beam sensor, compact range (M18, Compact Range 0, I, II, and III), and modular (Modular Range II) sensors.

Thru-Beam

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Thru-Beam sensors consist of a transmitter and a receiver. The transmitter sends a narrow continuous tone. When a target is positioned between the transmitter and the receiver the tone is interrupted, which causes the output of the receiver to change state. The operating voltage is 20-30 VDC. The switching frequency is 200 Hz at 40 cm sensing distance.

Thru-Beam Receivers

There are two receivers available for the Thru-Beam sensors. Both use a PNP transistor. One receiver provides a normally open (NO) contact and the other provides a normally closed (NC) contact.

The sensitivity and frequency setting of the Thru-Beam sensors is a function of the X1 connection on the receiver. Receiver Distance (cm) X1 Open X1 to LX1 to L+

5-150 5-80 5-40

Switching Frequency (Hz) 100 150 200

The minimum size of a detectable object is a function of the distance between the transmitter and the receiver. If the distance between the transmitter and the receiver is less than 40 cm and the minimum gap width between two objects is at least 3 cm, objects of 2 cm or larger will be detected. If the distance between the sensors is less, even gaps of less than 1 mm can be detected. At maximum sensing distance, objects greater than 4 cm will be detected, provided the gap between objects is greater than 1 cm.

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Compact Range 0

Compact Range 0 sensors are available with an integrated or an separate transducer. They are configured with a normally open (NO), normally closed (NC) or analog output. These sensors have a cubic shape (88 x 65 x 30 mm). The sensors operate on 18 35 VDC and can handle a load up to 100 mA.

Depending on the sensor, the sensing range is either 6 - 30 cm (separate transducer) or 20 - 100 cm (integrated transducer). Switching frequencies vary from 5 Hz to 8 Hz. Compact Range 0 sensors have background suppression. This means the upper limit of the sensing range is adjustable with a potentiometer. Targets within the sensing range but beyond the switching range of the upper limit will not be detected.

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Compact Range I

Compact Range I sensors are available with a normally open (NO) or a normally closed (NC) contact. They are also available with two outputs, one normally open (NO) and one normally closed (NC). These sensors have a cylindrical shape (M30 x 150 mm). Several versions are available, including a separate transducer (shown) and a tilting head (not shown). The sensors operate on 20 - 30 VDC and can handle a load up to 200 mA.

Depending on the sensor the sensing range is either 6 - 30 cm, 20 - 130 cm, 40 - 300 cm, or 60 - 600 cm. Switching frequencies vary from 1 Hz to 8 Hz. Compact Range I sensors have background and foreground suppression. This means the upper and lower limits of the sensing range are adjustable with separate potentiometer. Targets within the sensing range but beyond the switching range of the upper and lower limits will not be detected.

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SONPROG

The ultrasonic sensors discussed so far (Thru-Beam, Compact Range 0, and Compact Range I) are either nonadjustable or can be adjusted manually with potentiometers. SONPROG is a computer program, unique to Siemens, that is used to adjust Compact Range II, Compact Range III, and Compact Range M18 sensors. Sensor Thru-Beam Compact Range Compact Range Compact Range Compact Range Compact Range

Adjustment None 0 1 Potentiometer I 2 Potentiometers II SONPROG III SONPROG M18 SONPROG

With SONPROG sonar sensors can be matched individually to the requirements of a particular application. An interface is connected between the sensor and an RS232 port of a computer. SONPROG can be used to set the following parameters: • • • • • • •

Beginning and end of switching range Switching hysteresis Beginning and end of analog characteristic End of blind zone End of sensing range NO/NC contacts Potentiometer adjustments on sensors on/off

These values can be printed out and stored in a file. They are immediately available when needed. When replacing a sensor, for example, the stored parameters can be easily applied to the new sensor.

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Compact Range II

Compact Range II sensors are similar in appearance to Compact Range I sensors. A major difference is that Compact Range II sensors can be adjusted manually or with SONPROG. They are available with a normally open (NO) or a normally closed (NC) contact. They are also available with two outputs, one normally open (NO) and one normally closed (NC). These sensors have a cylindrical shape (M30 x 150 mm). Several versions are available, including a separate transducer. The sensors operate on 20 - 30 VDC and can handle a load up to 300 mA. Compact Range II sensors can be synchronized to prevent mutual interference when using multiple sensors in close proximity to each other.

Depending on the sensor the sensing range is either 6 - 30 cm, 20 - 130 cm, 40 - 300 cm, or 60 - 600 cm. Switching frequencies vary from 1 Hz to 8 Hz. Compact Range II sensors have background and foreground suppression.

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Compact Range II Analog Version

An analog version of the Compact Range II sensor is available. The analog measurement is converted by the sensor to digital pulses. A counter in LOGO! or a PLC counts the pulses and makes the measurement conversion. If, for example, the switching output of the sensor were set such that 50 Hz was equivalent to 50 cm and the gate time of LOGO! was set for 1 second, LOGO! would be able to accurately convert any frequency to its corresponding distance.

Compact Range III

Like the Compact Range II sensors, Compact Range III sensors can be adjusted manually or with SONPROG. They are available with a normally open (NO) or a normally closed (NC) contact. They are also available with two analog outputs, 0 - 20 mA or 0 10 VDC. The sensors operate on 20 - 30 VDC and can handle a load up to 300 mA. Compact Range III sensors can be synchronized to prevent mutual interference when using multiple sensors in close proximity to each other. In addition, they offer an arithmetic mean feature. This is useful for liquid level sensing or other applications where reflection variations can occur. The arithmetic mean feature helps compensate for these variations.

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Depending on the sensor, the sensing range is either 6 - 30 cm, 20 - 130 cm, 40 - 300 cm, 60 - 600 cm, or 80 - 1000 cm. Switching frequencies vary from 0.5 Hz to 5 Hz. Compact Range III sensors have background and foreground suppression.

Compact Range M18

The small size (M18 x 101 mm) of the Compact Range M18 sensor makes it suited for applications where space is limited. Compact Range M18 sensors are available with a normally open (NO) or a normally closed (NC) contact. They are also available with an analog output (4 - 20 mA, 0 - 20 mA, or 0 - 10 VDC). The sensors operate on 20 - 30 VDC and can handle a load up to 100 mA.

Depending on the sensor the sensing range is either 5 - 30 cm or 15 - 100 cm and the switching frequency is either 4 or 5 Hz. Compact Range M18 sensors have background suppression.

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Compact Range with for use with AS-i

Siemens also manufactures ultrasonic sensors for use with AS-i. Four sensing ranges are available: 6 - 30 cm, 20 - 130 cm, 40 - 300 cm, and 60 - 600 cm. The switching frequency varies from 1 to 8 Hz.

Modular Range II and the Signal Evaluator

The next group of ultrasonic sensors is Modular Range II. The Modular Range II consists of sensors and their corresponding signal evaluator. The signal evaluator is required for Modular Range II sensors. Sensor values are set using buttons on the evaluator. A two-line LCD displays the set values.

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The signal evaluator can operate a maximum of two Modular Range II sensors. It is supplied with a 20 - 30 VDC power supply. It has two switching outputs, one error output, and one analog output.

Modular Range II Sensors

Module Range II sensors are available in three versions: cubic sensors, cylindrical sensors, and spherical sensors. They have analog and normally open (NO) or normally closed (NC) outputs. As mentioned earlier, all settings and operations are done with a signal evaluator.

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Depending on the sensor the sensing range is either 6 - 30 cm, 20 - 130 cm, 40 - 300 cm, 60 - 600 cm, or 80 - 1000 cm. Switching frequencies vary from 1 Hz to 20 Hz. Modular Range II sensors have background and foreground suppression.

Accessories

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An adjusting device with a mounting flange (shown) or bracket (not shown) and a 90° diverting reflector are available for M30 spherical sensors. The adjusting device allows the sensor to be positioned in hard-to-mount areas.

Review 6 1)

Ultrasonic ____________-____________ proximity sensors require a separate transmitter and receiver.

2)

If X1 is connected to L+ of a Thru-Beam ultrasonic proximity sensor, the sensing range is ____________ to ____________ cm.

3)

The maximum sensing range of a Compact Range 0 ultrasonic sensor with a ____________ transducer is 6 - 30 cm.

4)

Compact Range ____________ does not offer foreground suppression. a. 0 b. I c. II d. III

5)

____________ is a computer program used to adjust Compact Range II, Compact Range III, and Compact Range M18 ultrasonic sensors.

6)

____________ Range II require a signal evaluator.

7)

A signal evaluator can operate a maximum of ____________ sensors. a. 1 b. 2 c. 3 d. 4

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Photoelectric Sensors Theory of Operation

A photoelectric sensor is another type of position sensing device. Photoelectric sensors, similar to the ones shown below, use a modulated light beam that is either broken or reflected by the target.

The control consists of an emitter (light source), a receiver to detect the emitted light, and associated electronics that evaluate and amplify the detected signal causing the photoelectric’s output switch to change state. We are all familiar with the simple application of a photoelectric sensor placed in the entrance of a store to alert the presence of a customer. This, of course, is only one possible application.

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Modulated Light

Modulated light increases the sensing range while reducing the effect of ambient light. Modulated light is pulsed at a specific frequency between 5 and 30 KHz. The photoelectric sensor is able to distinguish the modulated light from ambient light. Light sources used by these sensors range in the light spectrum from visible green to invisible infrared. Light-emitting diode (LED) sources are typically used.

Clearance

It is possible that two photoelectric devices operating in close proximity to each other can cause interference. The problem may be rectified with alignment or covers. The following clearances between sensors are given as a starting point. In some cases it may be necessary to increase the distance between sensors.

Sensor Model D4 mm / M5 M12 M18 K31 K30 K40 K80 L18 L50 (Diffuse) L50 (Thru-Beam)

Distance 50 mm 250 mm 250 mm 250 mm 500 mm 750 mm 500 mm 150 mm 30 mm 80 mm

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Excess Gain

Many environments, particularly industrial applications, include dust, dirt, smoke, moisture, or other airborne contaminants. A sensor operating in an environment that contains these contaminants requires more light to operate properly. There are six grades of contamination: 1. 2. 3. 4. 5. 6.

Clean Air (Ideal condition, climate controlled or sterile) Slight Contamination (Indoor, nonindustrial areas, office buildings) Low Contamination (Warehouse, light industry, material handling operations) Moderate Contamination (Milling operations, high humidity, steam) High Contamination (Heavy particle laden air, extreme wash down environments, grain elevators) Extreme/Severe Contamination (Coal bins, residue on lens)

Excess gain represents the amount of light emitted by the transmitter in excess of the amount required to operate the receiver. In clean environments an excess gain equal to or greater than 1 is usually sufficient to operate the sensor’s receiver. If, for example, an environment contained enough airborne contaminants to absorb 50% of the light emitted by the transmitter, a minimum excess gain of 2 would be required to operate the sensor’s receiver. Excess gain is plotted on a logarithmic chart. The example shown below is an excess gain chart for an M12 thru-beam sensor. If the required sensing distance is 1 m there is an excess gain of 30. This means there is 30 times more light than required in clean air hitting the receiver. Excess gain decreases as sensing distance increases. Keep in mind that the sensing distance for thru-beam sensors is from the transmitter to the receiver and the sensing distance for reflective sensors is from the transmitter to the target.

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Switching Zones

Photoelectric sensors have a switching zone. The switching zone is based on the beam pattern and diameter of the light from the sensor’s emitter. The receiver will operate when a target enters this area.

Symbols

Various symbols are used in the Sensor catalog (SFPC-08000) to help identify the type of photoelectric sensor. Some symbols are used to indicate a sensor’s scan technique, such as diffuse, retroreflective, or thru beam. Other symbols identify a specific feature of the sensor, such as fiber-optics, slot, or color sensor.

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Scan Techniques

A scan technique is a method used by photoelectric sensors to detect an object (target). In part, the best technique to use depends on the target. Some targets are opaque and others are highly reflective. In some cases it is necessary to detect a change in color. Scanning distance is also a factor in selecting a scan technique. Some techniques work well at greater distances while others work better when the target is closer to the sensor.

Thru-Beam

Separate emitter and receiver units are required for a thru-beam sensor. The units are aligned in a way that the greatest possible amount of pulsed light from the transmitter reaches the receiver. An object (target) placed in the path of the light beam blocks the light to the receiver, causing the receiver’s output to change state. When the target no longer blocks the light path the receiver’s output returns to its normal state. Thru-beam is suitable for detection of opaque or reflective objects. It cannot be used to detect transparent objects. In addition, vibration can cause alignment problems. The high excess gain of thru-beam sensors make them suitable for environments with airborne contaminants. The maximum sensing range is 300 feet.

Thru-Beam Effective Beam

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The effective beam of a photoelectric sensor is the region of the beam’s diameter where a target is detected. The effective beam on a thru-beam sensor is the diameter of the emitter and receiver lens. The effective beam extends from the emitter lens to the receiver lens. The minimum size of the target should equal the diameter of the lens.

Reflective or Retroreflective Scan

Reflective and retroreflective scan are two names for the same technique. The emitter and receiver are in one unit. Light from the emitter is transmitted in a straight line to a reflector and returns to the receiver. A normal or a corner-cube reflector can be used. When a target blocks the light path the output of the sensor changes state. When the target no longer blocks the light path the sensor returns to its normal state. The maximum sensing range is 35 feet.

Retroreflective Scan Effective Beam

The effective beam is tapered from the sensor’s lens to the edges of the reflector. The minimum size of the target should equal the size of the reflector.

Reflectors

Reflectors are ordered separately from sensors. Reflectors come in various sizes and can be round or rectangular in shape or reflective tape. The sensing distance is specified with a particular reflector. Reflective tape should not be used with polarized retroreflective sensors.

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Retroreflective Scan and Shiny Objects

Retroreflective scan sensors may not be able to detect shiny objects. Shiny objects reflect light back to the sensor. The sensor is unable to differentiate between light reflected from a shiny object and light reflected from a reflector.

Polarized Retroreflective Scan

A variation of retroreflective scan is polarized retroreflective scan. Polarizing filters are placed in front of the emitter and receiver lenses. The polarizing filter projects the emitter’s beam in one plane only. This light is said to be polarized. A corner-cube reflector must be used to rotate the light reflected back to the receiver. The polarizing filter on the receiver allows rotated light to pass through to the receiver. In comparison to retroreflective scan, polarized retroreflective scan works well when trying to detect shiny objects.

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Diffuse Scan

The emitter and receiver are in one unit. Light from the emitter strikes the target and the reflected light is diffused from the surface at all angles. If the receiver receives enough reflected light the output will switch states. When no light is reflected back to the receiver the output returns to its original state. In diffuse scanning the emitter is placed perpendicular to the target. The receiver will be at some angle in order to receive some of the scattered (diffuse) reflection. Only a small amount of light will reach the receiver, therefore, this technique has an effective range of about 40” .

Diffuse Scan Correction Factors

The specified sensing range of diffuse sensors is achieved by using a matte white paper. The following correction values may be applied to other surfaces. These values are guidelines only and some trial and error may be necessary to get correct operation. Test Card (Matte White) White Paper Gray PVC Printed Newspaper Lightly Colored Wood Cork White Plastic Black Plastic Neoprene, Black Automobile Tires Aluminum, Untreated Aluminum, Black Anodized Aluminum, Matte (Brushed Finish) Stainless Steel, Polished

100% 80% 57% 60% 73% 65% 70% 22% 20% 15% 200% 150% 120% 230%

87

Diffuse Scan with Background Suppression

Diffuse scan with background suppression is used to detect objects up to a certain distance. Objects beyond the specified distance are ignored. Background suppression is accomplished with a position sensor detector (PSD). Reflected light from the target hits the PSD at different angles, depending on the distance of the target. The greater the distance the narrower the angle of the reflected light.

Diffuse Scan Effective Beam

The effective beam is equal to the size of the target when located in the beam pattern.

88

Operating Modes

There are two operating modes: dark operate (DO) and light operate (LO). Dark operate is an operating mode in which the load is energized when light from the emitter is absent from the receiver.

Light operate is an operating mode in which the load is energized when light from the emitter reaches the receiver.

The following table shows the relationship between operating mode and load status for thru, retroreflective, and diffuse scan.

Operating Mode

Light Path

Load Status Thru San and Diffuse Retroreflective Light Operate (LO) Not Blocked Energized Deenergized Blocked Deenergized Energized Dark Operate (DO) Not Blocked Deenergized Energized Blocked Energized Deenergized

89

Fiber Optics

Fiber optics is not a scan technique, but another method for transmitting light. Fiber optic sensors use an emitter, receiver, and a flexible cable packed with tiny fibers that transmit light. Depending on the sensor there may be a separate cable for the emitter and receiver, or it may use a single cable. When a single cable is used, the emitter and receiver use various methods to distribute emitter and transmitter fibers within a cable. Glass fibers are used when the emitter source is infrared light. Plastic fibers are used when the emitter source is visible light.

Fiber optics can be used with thru-beam, retroreflective scan, or diffuse scan sensors. In thru beam light is emitted and received with individual cables. In retroreflective and diffuse scan light is emitted and received with the same cable (bifurcated). Fiber optics is ideal for small sensing areas or small objects. Fiber optics have a shorter sensing range due to light losses in the fiber optic cables.

90

Lasers

Lasers are sometimes used as sensor light sources. Siemens uses Class 2 lasers which have a maximum radiant power of 1 mW. Class 2 lasers require no protective measures and a laser protection officer is not required. However, a warning notice must be displayed when laser sensors are used. Laser sensors are available in thru-beam, diffuse scan, and diffuse scan with background suppression versions. Lasers have a high intensity visible light, which makes setup and adjustment easy. Laser technology allows for detection of extremely small objects at a distance. The Siemens L18 sensor, for example, will detect an object of 0.03 mm at a distance of 80 cm. Examples of laser sensor applications include exact positioning, speed detection, or checking thread thickness of 0.1 mm and over.

91

Review 7 1)

Modulated light of a Siemens photoelectric sensor is pulsed at a frequency between ____________ and __________ KHz.

2)

Excess ____________ is a measurement of the amount of light falling on the receiver in excess of the minimum light required to operate the sensor.

3)

____________ is a scan technique in which the emitter and receiver are in one unit. Light from the emitter is transmitted in a straight line to a reflector and returned to the receiver.

4)

Polarizing filters on a retroreflective scan sensor orientate planes of light ____________ degrees to one another.

5)

The correction factor for diffuse scan of cork with a photoelectric sensor is ____________ %.

6)

____________ operate is an operating mode in which the load is energized when light from the emitter of a photoelectric sensor is absent from the receiver.

7)

Fiber optics is a scan technique. a. true b. false

8)

92

Siemens laser photoelectric sensors use Class ____________ lasers.

Photoelectric Family of Sensors

Siemens offers a wide variety of photoelectric sensors, including thru-beam, retroreflective scan, and diffuse scan sensors. There are many photoelectric sensors to choose from. Choice depends on many factors such as scan mode, operating voltage, environment, and output configurations. Most of these sensors can be used with some or all scan techniques. In addition, specialized sensors such as fiber optic, laser, and color sensors are available. To help simplify the process of determining the right sensor selection guides are provided. These guides do not list all the features of a given sensor. For a more detailed description refer to the appropriate catalog.

93

Thru-Beam Sensors Sensor

Range

D4/M5 M12 M18 M18M M18P K30 K35 K40 K50

250 mm 4m 6m 12 m 12 m 12 m 5m 15 m 5m

K65 K80 L18 (Laser)

Voltage

10-30 VDC 10-30 VDC 10-36 VDC 10-30 VDC 10-30 VDC 10-36 VDC 10-30 VDC 10-36 VDC 10-30 VDC 15-264 VAC 50 m 10-30 VDC 50 m 10-36 VDC 20-320 VAC 50 m 10-30 VDC

Output Mode PNP NPN Relay DO LO X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

X X

X

X

X X

X X

X

X

Connection Housing AS-i M8 M12 Cable Terminals X X Metal X X Metal X X Metal X X Metal X X Plastic X X Plastic X X Plastic X X X Plastic X X X Plastic

X

X X

X

X

X

X

Plastic Plastic Metal

Retroreflective Sensors Sensor

Range

M12 M18 M18M M18P K20 K30 K35 K40 K50

1.5 m 2m 2m 2m 2.5 m 4m 2.5 m 6m 4m

K65 K80 L50 (Laser) Light Array C40

94

Voltage

10-30 VDC 10-36 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-36 VDC 10-30 VDC 10-36 VDC 10-30 VDC 15-264 VAC 8m 10-30 VDC 6m 10-36 VDC 20-320 VAC 12 m 10-30 VDC

Output Mode PNP NPN Relay DO LO X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

X X

X

X

1.4 m

12-36 VDC

X

6m

10-36 VDC

X

X

X X

X X

X

X

X X

X

Connection Housing AS-i M8 M12 Cable Terminals X X Metal X X Metal X X Metal X X Plastic X X Plastic X X Plastic X X Plastic X X X Plastic X X X Plastic

X

X X

X

X

X

X X

X

Plastic Plastic Metal Plastic

X

Plastic

Diffuse Sensors Sensor

Range

D4/M5 M12 M18 M18M M18P K20 K30 K35 K40 K50

50 mm 30 cm 60 cm 30 cm 30 cm 30 cm 1.2 m 50 cm 2m 90 cm

K65 K80 C40

Voltage

10-30 VDC 10-30 VDC 10-36 VDC 10-30 VDC 10-30 VDC 10-30 VDC 10-36 VDC 10-30 VDC 10-36 VDC 10-30 VDC 15-264 VAC 2m 10-30 VDC 2m 10-36 VDC 20-320 VAC 2.5 cm 10-30 VDC

Output Mode PNP NPN Relay DO LO X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

X X

X

X

X

X X

X X

X

X

AS-i M8 X

X X X X X

X

Connection Housing M12 Cable Terminals X Metal X X Metal X X Metal X X Metal X X Plastic X Plastic X Plastic X Plastic X X Plastic X X Plastic X X

X X

X


Diffuse Sensors with Background Suppression Sensor

Range

M18 M18P K20 K50

120 mm 100 mm 100 mm 25 cm

K65 K80 L50 (Laser) C40

Voltage

10-36 VDC 10-30 VDC 10-30 VDC 10-30 VDC 15-264 VAC 50 cm 10-30 VDC 1m 10-36 VDC 20-320 VAC 150 mm 10-30 VDC 2.5 cm 10-30 VDC

Output Mode PNP NPN Relay DO LO X X X X X X X X X X X X X X X X X X X

X X

X X

X X

X

X

X

X

X

X

X

Connection Housing AS-i M8 M12 Cable Terminals X X Metal X X Plastic X X Plastic X X X Plastic X X

X

X

X

X

X

X

X

X

Plastic Plastic Metal Plastic

95

Teach In

Some of the following sensors, such as the CL40, have a feature known as Teach In. This feature allows the user to teach the sensor what it should detect. An object to be detected is placed in front of the sensor so that it knows what the accepted reflected light is. The sensor is then programmed to respond only to this light. The CL40 uses a “SET” button to Teach In. Other sensors have different methods to Teach In. Teach In can be used to detect a specific color, for example. Teach In also works to detect transparent objects.

Fiber Optic Sensors

The basic operation is the same for optical fibers made of glass or plastics. Optical fibers are fitted in front of the transmitter and receiver and extend the “eye” of the sensor. Fiber optic cables are small and flexible and can be used for sensing in hard to access places.

96

Laser Diffuse Sensor with Analog Output

The analog laser sensor is able to measure the exact distance of an object within its sensing range. This sensor uses a visible laser light with a highly accurate and linear output.

Color BERO

The color BERO uses 3 LEDs with the colors red, green, and blue. Light is emitted to the target and can detect a specific color of reflected light. This sensor uses Teach In to set the color to be detected. The CL40 is also a fiber optic device.

Color Mark BERO

The color mark BERO is also used to detect specific colors. This sensor works differently from the CL40. The color mark BERO uses green or red light for the emitter. The color is selected dependent on the contrast of the target. The target and background color can be set separately.

97

Slot BERO

The target is placed inside the slot of the sensor. Emitted light passes through the object. Different contrast, tears, or holes in the target will vary the quantity of light reaching the receiver. This sensor uses Teach In. It is available with infrared or visible red/green light

Selection Guide Sensor Type Fiber Optic

Laser Diffuse Analog Output Color BERO Color Mark BERO Slot BERO

Sensor

Range

Voltage

K35 KL40 K30 K40 L50

75 mm 280 mm 120 mm 150 cm 45-85 mm

10-30 VDC 10-30 VDC 10-36 VDC 10-36 VDC 18-28 VDC

CL40

15 mm 10-30 VDC

X

X

C80

18 mm 10-30 VDC

X

X

X

X

G20

2 mm

10-30 VDC

Teach Output In PNP NPN X X X X X X X X X

X

X

Mode DO LO X X X X X X X X

X

X

X

X

X

X

Connection Housing M8 M12 Cable X X Plastic X X Plastic X X Plastic X X X Plastic X Plastic

X X

X

Plastic

X

Metal

X

Metal

Review 8 1)

The maximum sensing range of a K80, thru scan, photoelectric sensor is ____________ m.

2)

____________ is an example of a photoelectric sensor with Teach In. a. D4 b. K50 c. CL40 d. K30

98

3)

A ____________ is a photoelectric sensor that has a slot where the target is placed.

4)

The maximum sensing range of a Color Mark BERO C80 is ____________ mm.

Sensor Applications

There are any number of applications where sensors can be utilized, and as you have seen throughout this book there are a number of sensors to chose from. Choosing the right sensor can be confusing and takes careful thought and planning. Often, more than one sensor will do the job. As the application becomes more complex the more difficult it is to choose the right sensor for a given application. The following application guide will help you find the right sensor for the right application.

For further application assistance contact your local sales office. Call (800) 964-4414 for nearest office.

99

Ultrasonic Sensors Application Level Measurement in Large Vessels (Tanks, Silos) Sensor 3RG61 13 Compact Range III

Application Level Measurement in Small Bottles Sensor 3RG61 12 Compact Range III

Sensor 3RG60 14 Compact Range I

Application Height Sensing Sensor 3RG60 13 Compact Range II

Application Quality Control

Application Breakage Sensing

Sensor 3RG61 12 Compact Range III

Sensor 3RG61 12 Compact Range I

Application Bottle Counting

Application Object Sensing

Sensor 3RG62 43 Thru Beam

Sensor 3RG60 12 Compact Range II

Application Vehicle Sensing and Positioning

Application Stack Height Sensing

Sensor 3RG60 14 Compact Range III

100

Application Anti-Collision

Sensor 3RG60 13 Compact Range II


Ultrasonic Sensors Application Contour Recognition Sensor 3RG61 13 Compact Range III

Application People Sensing Sensor 3RG60 12 Compact Range II

Application Diameter Sensing and Strip Speed Control Sensor 3RG61 12 Compact Range III

Application Wire and Rope Breakage Monitoring Sensor 3RG60 12 Compact Range I

Application Loop Control Sensor 3RG60 15 Compact Range II


101

Photoelectric Sensors Application Verifying Objects in Clear Bottles

Application Flow of Pallets Carrying Bottles

Sensor M12 Thru Beam

Sensor K40 Retroreflective

Application Counting Cans

Application Counting Bottles

Sensor K50 Polarized Retroreflective

Sensor SL18 Retroreflective

Application Counting Cartons

Application Car Wash


Sensor SL Thru Beam

Application Reading Reference Marks for Trimming

Application Detecting Persons

Sensor C80 Mark Sensor

Application Controlling Parking Gate Sensor SL Retroreflective

102


Application End of Roll Detection Sensor K31 Diffuse


Photoelectric Sensors Application Detecting Tab Threads Sensor KL40 Fiber Optic

Application Counting Packages Sensor K80 Retroreflective

Application Detecting Caps on Bottles Sensor K20 Diffuse with Background Suppression and K31 Thru Beam Application Detecting Components Inside Metal Can Sensor K50 Background Suppression

Application Determining Orientation of IC Chip

Application Detecting Items of Varying Heights

Sensor L50 Laser with Background Suppression

Sensor K80 Background Suppression

Application Detecting Orientation of IC Chip

Application Controlling Height of a Stack

Sensor Color Mark or Fiber Optic

Sensor SL Thru Beam

Application Detecting Jams on a Conveyor

Application Counting Boxes Anywhere on a Conveyor


Sensor SL18 Right Angle Retroreflective


103

Photoelectric Sensors Application Counting IC Chip Pins Sensor KL40 Fiber Optic

Application Batch counting and Diverting Cans Without Labels Sensor K40 Polarized

Application Detecting Presence of Object to Start a Conveyor Sensor K35 Retroreflective

Application Verifying Liquid in Vials Sensor K35 Fiber Optic

Application Verifying Cakes are Present in Transparent Package Sensor KL40 Fiber Optic

104

Application Detecting Reflective Objects Sensor K80 Polarized Retroreflective

Application Verifying Screws are Correctly Seated Sensor KL40 Fiber Optic

Application Verifying Lipstick Height Before Capping Sensor M5 or M12 Thru Beam

Application Detecting Labels with Transparent Background

Application Monitoring Objects as they Exit Vibration Bowl

Sensor G20 Slot Sensor

Sensor K35 Fiber Optic


Proximity Switches Application Detecting the Presence of a Broken Drill Bit Sensor 12 mm Normal Requirements

Application Detecting Presence of Set Screws on Hub for Speed or Direction Control

Application Detecting Milk in Cartons Sensor Capacitive

Application Controlling Fill level of solids in a bin Sensor Capacitive

Sensor 30mm Shorty

Application Detecting Full Open or Closed Valve Postition

Application Detecting Presence of Can and Lid

Sensor 12mm or 18mm Extra Duty

Sensor 30mm Normal Requirements or UBERO, 18mm Normal Requirements Gating Sensor

Application Detecting Broken Bit on Milling Machine Sensor 18 mm


105

Application Inquiry Providing a sensing device solution requires both knowledge of the application and answers to specific questions to obtain key additional facts. This page is intended to be photocopied and used as a self-help guide in assessing the scope of sensor applications. The information recorded on this form may then be cross-checked with the product specifications found in our “BERO - Sensing Solutions” catalog to obtain a potential solution to your application. If your application involves machine guard safety interlocking, the use of standard position sensors could result in serious injury or death. Please contact SE&A Sensor Marketing for assistance at (630) 879-6000. 1.

2.

3.

Target Material ___ Metal ___ Non-Metal ___ Ferrous ___ Non-Ferrous ___ Transparent ___ Translucent ___ Opaque Target Description and Dimensions Target Finish (shiny/dull/matte, etc.) __________ Target Color __________ Target Texture __________ Target Orientation/Spacing Describe position of target when sensed relative to immediate environment. Number of Multiple Targets ____ Number of Targets Nested Together ___ Spacing Between Targets _______ Size of Target __________

4.

Target Movement/Speed/Velocity Describe how the target approaches the sensing area (Axial/Lateral). Target Speed __________ Cycles per Second/Minute/etc ______ Hours machine is run? ________

5.

6.

106

Sensing Distance From Target to Sensor __________ From Target to Background __________ Background Description Describe the background conditions.

7.

Physical/Mounting Criteria Is target accessible from more than one side? Space available to install sensor _____ Sensor Orientation Possibilities _____ _________________________________

8.

Environment ___ Clean ___ Oily ___ Dusty ___ Humid ___ Outdoor ___ Indoor ___ Submersion ___ Wash down Temperature ________ Temperature Variation ________

9.

Load Requirements Describe the Load _________________ Inductive: Inrush _____ Sealed _____

10. Control Voltage Supply __________ VAC __________ VDC 11. Output Requirements ___ NPN ___ PNP ___ SCR ___ FET ___ Relay ___ Normally Open ___ Normally Closed ___ Complimentary _____ LO/DO 12. Connection Preference ___ Connector/Matching Cordset Length of Sensor Prewired Cable (2 Meters Standard) ________ ___ AS-i Interface


Review Answers

Review 1

1) Limit switch; 2) d; 3) Pretravel; 4) operating position; 5) break-before-make; 6) Break; 7) 30; 8) operating head; 9) SIGUARD; 10) 6P

Review 2

1) inductive; 2) a; 3) 3; 4) 4; 5) steel; 6) 0.40; 7) 81%

Review 3

1) 10; 2) 20; 3) 265, 320; 4) IP; 5) 65; 6) UBERO

Review 4

1) electrostatic; 2) any; 3) dielectric; 4) b; 5) 20

Review 5

1) sound; 2) 6-80; 3) 5; 4) 60; 5) 3; 6) Diffuse

Review 6

1) Thru-Beam; 2) 5 to 40; 3) separate; 4) a; 5) SONPROG; 6) Modular; 7) b

Review 7

1) 5 and 30; 2) gain; 3) Retroreflective; 4) 90 degrees; 5) 65; 6) Dark; 7) b; 8) 2

Review 8

1) 50; 2) c; 3) G20; 4) 18

107

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer card is provided. After completing the final exam, mail in the answer card for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. Questions

1.

The distance an actuator arm travels on a mechanical limit switch from the release position to the free position is known as ____________ . a. c.

2.

b. d.

Break Inductive

International and IEC International and North American North American and BERO International and BERO

Photoelectric Inductive

b. d.

Ultrasonic Capacitive

When two or more shielded inductive proximity sensors are mounted opposite one another, they should be placed a distance of at least ____________ times the rated sensing range from each other. a. c.

108

Make Continuous

____________ is a type of sensor that can only detect metal. a. c.

5.

Differential Travel Release Travel

____________ are the two product lines for Siemens mechanical limit switches. a. b. c. d.

4.

b. d.

____________ is a term that describes the load a mechanical limit switch can handle when the mechanical contacts close. a. c.

3.

Overtravel Pretravel

two four

b. d.

three six

6.

A correction factor of ____________ is applied to an unshielded inductive proximity switch when the target is 50% smaller than the standard target. a. c.

7.

4 8

b. d.

6 10

Inductive Photoelectric

b. d.

Ultrasonic Capacitive

The approximate angle of the main cone of an ultrasonic sensor is ____________ degrees. a. c.

11.

NAMUR UBERO Increased Operating Distance AS-i

____________ proximity sensors develop an electrostatic field to detect the target. a. c.

10.

0.73 0.92

When using a capacitive proximity sensor with a rated sensing distance of 10 mm to detect polyamide, the effective sensing distance is approximately ____________ mm. a. c.

9.

b. d.

____________ is a type of Siemens inductive proximity switch that can detect all metal targets without a reduction factor. a. b. c. d.

8.

0.50 0.83

5 30

b. d.

10 45

A distance greater than ____________ cm should be left between two ultrasonic sensors mounted opposite each other with a rated sensing range of 20 - 130 cm. a. c.

4000 1200

b. d.

2500 400

109

12.

Coarse-grained materials can have as much as ____________ degrees angular deviation from the send direction of an ultrasonic sensor. a. c.

13.

3.6 25 - 33

Compact Range 0 Compact Range I Compact Range III Modular Range II

X1 is open X1 is connected to L+ X1 is connected to LX1 is closed

Thru Beam Compact Range 0 and Compact Range I Compact Range I and Compact Range II Compact Range II and Compact Range III

A 90° diverting reflector is available for use with ____________ ultrasonic sensors. a. b. c. d.

110

b. d.

SONPROG can be used to adjust ____________ ultrasonic sensors. a. b. c. d.

17.

0.17 5

The maximum sensing distance of a Thru Beam ultrasonic sensor is 80 cm when ____________ . a. b. c. d.

16.

5 90

A signal evaluator is required for use with ____________ ultrasonic sensors. a. b. c. d.

15.

b. d.

Sound velocity decreases ____________ % between sea level and 3000 m above sea level. a. c.

14.

3 45

M30 spherical Compact Range M18 spherical Compact Range 0 with Integrated Transducer Thru Beam

18.

____________ scan is a photoelectric scan technique in which the planes of emitter light and reflected light are orientated 90° to one another. a. b. c. d.

19.

____________ is a photoelectric sensor that use three LEDs with colors red, green, and blue and is can be used to detect a specific color of reflected light. a. c.

20.

Polarized Retroreflective Retroreflective Diffuse Thru

G20 CL40

b. d.

K30 C80

The maximum sensing range of the L18 laser photoelectric sensor is ____________ . a. b. c. d.

12 m 50 m 100 mm 150 mm

111

Notes

112

Table of Contents

Introduction ..............................................................................2 Siemens Safety Switches .........................................................4 Switch Symbols ........................................................................7 Need For Circuit Protection.......................................................9 Fuses ...................................................................................... 17 Fuse Ratings And Classifications ............................................21 Enclosures ..............................................................................24 Switch Design.........................................................................31 Safety Switch Ratings .............................................................38 Switch Circuit Types And Terminology .....................................41 Catalog Numbers ....................................................................45 General Duty Safety Switches ................................................49 Heavy Duty Safety Switches ..................................................52 Selecting Safety Switches ......................................................61 Review Answers ..................................................................... 71 Final Exam ..............................................................................72

1

Introduction

Welcome to another course in the STEP (Siemens Technical Education Program) series, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Safety Switches and related products. Upon completion of Safety Switches you should be able to:

2

•


•

Identify fuse types and classes

•

Explain the basic construction and operation of a Siemens safety switch

•

Explain the operation and benefit of Siemens VBII Safety Switches and visible blade designs

•

Identify various types of Siemens safety switches

•

Explain the difference between fusible and non-fusible safety switches

•

Identify circuit protection ratings for various types of Siemens safety switches

•

Identify safety switch accessories

This knowledge will help you better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. You should complete Basics of Electricity before attempting Safety Switches. An understanding of many of the concepts covered in Basics of Electricity is required for Safety Switches. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. Speedfax is a registered trademark of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-2005, National Electrical Code Copyright ©, 2004, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories Inc. and UL are registered trademarks of Underwriters Laboratories Inc., Northbrook, IL 60062. Other trademarks are the property of their respective owners. National Electrical Manufacturers Association is located at 2101 L. Street, N.W., Washington, D.C. 20037. The abbreviation “NEMA” is understood to mean National Electrical Manufacturers Association.

3

Siemens Safety Switches

A switch is generally used for two purposes: 1) A disconnecting means for a service entrance 2) A disconnecting means and fault protection for motors A safety switch is simply a switch located in its own enclosure. The enclosure provides a degree of protection to personnel against incidental contact with live electrical equipment. It also provides protection to the enclosed equipment against specific environmental conditions. Safety switches may consist of a switch only, or may consist of a switch and fuses. There are two families of Siemens safety switches: general duty and heavy duty.

S Gener al Du ty

Heavy Duty

4

General Duty

Application

Safety switches can be used in any number of applications. The National Electrical Code® (NEC®), for example, requires that a disconnecting means shall be located in sight from the motor location and the driven machinery location (Article 430.102(B)). The NEC® defines “in sight” as visible and not more than 50 feet (15.24 m) distant (Article 100 - definitions). Regardless of where the safety switch is used, the function is to provide a means to connect and disconnect the load from its source of electrical power.

With power removed the operator can safely service the machinery without coming into contact with live electrical components or having the motor accidently start.

NEC® and the National Electrical Code® are registered trademarks of the National Fire Protection Association. Reprinted with permission from NFPA 70-2005, the National Electrical Code®, Copyright© 2004, National Fire Protection Association, Quincy, MA 02269.

5

Additional Information

This book offers an introduction to Safety Switches, but more information is available from your local Siemens sales representative.

Among the booklets available are the Safety Switch Application and Selection Guide, the Safety Switch Cross-Reference Guide, and the Safety Switch Replacement Parts Guide. World Wide Web

6

Information is also available by visiting the Siemenes Energy & Automation web site, at www.sea.siemens.com/dpd.

Switch Symbols

Switch Symbols

Symbols are used in a diagram to represent components. The symbol commonly used for a disconnect switch is shown below. The switch is normally shown in its “Off”, or “Open” state.

Two-Pole Non-Fused Switch

Fuse Symbols

Three-Pole Non-Fused Switch

Three-Pole Fused Switch

Fuses are represented in an electrical circuit by either of the following symbols:

7

Non-Fusible Safety Switch

A switch with no associated fuses is referred to as a nonfusible safety switch. A non-fusible safety switch has no circuit protection capability. It simply provides a convenient means to open and close a circuit. Opening the circuit disconnects the load from its source of electrical power, while closing the circuit connects the load. Circuit protection must be provided by external overcurrent devices such as circuit breakers or fuses. In the following illustration, power is supplied to a motor through a non-fusible safety switch and a separate fuse.

Non-Fusible Safety Switch

Fusible Safety Switch

A safety switch can be combined with fuses in a single enclosure. This is referred to as a fusible safety switch. The switch provides a convenient means to manually open and close the circuit, while the fuse provides overcurrent protection.


8

Fuse

Need For Circuit Protection

Current and Temperature

Current flow in a conductor always generates heat. The greater the current flow in a given size conductor, the hotter the conductor. Excess heat is damaging to electrical components and conductor insulation. For this reason conductors have a rated continuous current carrying capacity, or ampacity. Overcurrent protection devices, such as fuses, are used to protect conductors from excessive current flow. Fuses are designed to keep the flow of current in a circuit at a safe level to prevent the circuit conductors from overheating.

Normal Current Flow

Excessive Current Flow

Excessive current is referred to as overcurrent. The National Electrical Code® defines overcurrent as any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault (Article 100-definitions).


9

Overloads

An overload occurs when too many devices are operated on a single circuit, or if a piece of electrical equipment is made to work harder than it is designed to work. For example, a motor rated for 10 amperes may draw 20, 30, or more amperes in an overload condition. In the following illustration, a package has become jammed on a conveyor, causing the motor to work harder and draw more current. Because the motor is drawing more current, it heats up. Damage will occur to the motor in a short time if the problem is not corrected, or if the circuit is not shut down by the overcurrent protector.

Conductor Insulation

Motors, of course, are not the only devices that require circuit protection for an overload condition. Every circuit requires some form of protection against overcurrent and the heat it produces. For example, high levels of heat to insulated wire can cause the insulation to break down and flake off, exposing the conductors. Good Insulation

Insulation Affected by Heat

10

Short Circuits

When exposed conductors touch, a short circuit occurs, and the circuit resistance drops to nearly zero. Because of this very low resistance, short circuit current can be thousands of times higher than normal operating current. Conductor Insulation

Ohm’s Law shows the relationship of current, voltage, and resistance. For example, a 240 volt motor with 24 Ω(ohms) of resistance would normally draw 10 amperes of current. I=

E R

I=

240 24

I = 10 A

When a short circuit occurs, resistance drops dramatically. For example, if the above resistance dropped to 24 milliohms due to a short circuit, the current would increase to 10,000 amperes. I = 240 .024 I = 10,000 A

11

Preventing Damage

The heat generated by short-circuit current can rise to dangerous levels quickly, causing extensive damage to conductors and connected equipment. This heat-generating current must be interrupted as soon as possible after a short circuit occurs. Slight overcurrents can be allowed to continue for some period of time, but as the overcurrent magnitude increases, the protection device must act more quickly. In order to minimize costly damage, outright short circuits must be interrupted almost instantaneously.

$ $

$ $

$ $

Short-Circuit Current in Unprotected Electrical Circuits

$

$ $

When a short circuit occurs in an unprotected circuit, current will continue to flow until the circuit is damaged, or until the power is removed manually. The peak short-circuit current of the first cycle is the greatest, and is referred to as peak let-through current (IP). The electromagnetic force associated with this current can cause mechanical damage to electrical components. Peak Let-Thru Current (IP) + Direction Fault Occurs Time

0

- Direction

12

Normal Current

The maximum destructive energy let-through, I2t, is a measure of the energy associated with this current. It is capable of producing enough heat to melt conductors. 2

Peak Let-Thru Energy (I t) + D irection Fault Occurs Time 0

Normal Current - Direction

Short-Circuit Current in Protected Electrical Circuits

A properly used overcurrent protecting device will open the circuit quickly, limiting peak let-through current (IP) and energy (I2t). Peak Let-Thru Current (IP ) Peak Let-Thru Energy (I2 t)

+ D irection Fault Occurs

Time

0

- Direction

Article 240

Normal Current

Article 240 of the NEC® covers overcurrent protection. You are encouraged to become familiar with this material. Article 240.1 (FPN) states that overcurrent protection for conductors and equipment is provided to open the circuit if the current reaches a value that will cause an excessive or dangerous temperature in conductors or conductor insulation.


13

Ampacities of Insulated Conductors

How hot an insulated conductor can get before it sustains damage needs to be known. Conductors are rated by how much current they can carry on a continuous basis, known as ampacity. The following illustration is from NEC® Table 310.16. For example, a #8 American Wire Gauge (AWG) copper conductor with Type THW insulation is rated for 50 amperes at 75° C. A #1 AWG copper conductor with Type THW insulation rated at 75° C can carry 130 amperes. To avoid overloads and prevent insulation damage, it is necessary to keep the current from exceeding the conductor’s continuous current rating. Table 310.16 (partial). Allowable Ampacities of Insulated Conductors Rated 0 through 2000 Volts, 60ºC through 90ºC (140ºF through 194ºF) Not More than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30ºC (86ºF)

Size

Temperature Rating of Conductor 60ºC (140ºF) Types TW, UF

AWG or kcmil

75ºC (167ºF) Types FEPW, RH, RHW, THHW,THW, THWN, XHHW, USE, ZW

90ºC (194ºF) Types TBS,SA, SIS, FEP, FEPB, MI, RHH, RHW2, THHN, THHW, THW-2, THWN2, USE-2, XHH, XHHW, XHHW2, ZW-2

COPPER 18

—

—

14

16

—

—

18

14

20

20

25

12

25

25

30

10

30

35

40

8

40

50

55

6

55

65

75

4

70

85

95

3

85

100

110

2

95

115

130

1

110

130

150

1/0

125

150

170

2/0

145

175

195

3/0

165

200

225

4/0

195

230

260

NEC® Table 1 of Table 310.16 gives ampacities under two conditions: the raceway contains not more than three conductors, plus neutral, and the ambient temperature is not more than 30° C (86° F). If either of these two conditions is exceeded, the values shown must be reduced using derating values provided by NEC® (not shown here). 14

Sizing Conductors and Overcurrent Devices

According to the NEC®, a continuous load is a load where the maximum current is expected to continue for three hours or more (Article 100 - Definitions). The National Electrical Code® provides an example of conductor sizing and the rating of overcurrent protective devices in Article 210.20(A), which has to do with branch circuits.The rating of a branch-circuit overcurrent device serving continuous loads, such as store lighting, shall be not less than the noncontinuous load plus 125% of the continuous load. Exception: Circuits supplied by an assembly and overcurrent devices that are listed for continuous operation at 100% of their ratings. In this case, the continuous and noncontinuous loads are simply added. In general, an electrical conductor must be capable of carrying 125% of the full-load current. In a branch circuit, continuous loads such as mercantile lighting must not exceed 80% of the circuit rating. If an electric lighting circuit, for example, had a continuous current rating of 100 amperes, then the conductor would be sized to carry at least 125 amperes. In this example 100 amperes (lighting circuit load) is 80% of 125 amperes (conductor ampacity). Electric Lighting Circuit Rating = 100 amperes Conductor Ampacity = 125 amperes (100 amperes x 125%) There are exceptions and the NEC® must be consulted for each application. The exception given in the previous paragraph, for example, provides for 100% rating of a circuit if it is supplied by an overcurrent device and assembly rated for continuous operation. (This rating must be done by a qualified testing laboratory.) For more information on conductor sizing, see NEC® Articles 210.19(A), 210.20(A), and 384.16(D) in the 2005 code book.


15

Review 1 1.

A safety switch with fuses in a single enclosure is referred to as a ____________ safety switch.

2.

NEC® defines “in sight” as visible and not more than ____________ feet distant.

3.

With an increase in current, heat will a. increase b. decrease c. remain the same

4.

Two causes of overcurrent are ____________ and ______ ______ ____________ .

5.

A ____________ ____________ occurs when two bare conductors touch.

6.

An ____________ occurs when electrical equipment is required to work harder than it is rated.

7.

The peak short circuit current of the first cycle is known as ____________ ____________ - ____________.

8.

Peak let-thru ____________ is a destructive thermal force.

9.

Article ____________ of the NEC® covers overcurrent protection.

10. Table ____________ of the NEC® gives ampacities of insulated conductors. 11. In general, the electrical conductor must be capable of carrying ____________ % of the full-load current.

16

Fuses

Circuit protection would be unnecessary if overloads and short circuits could be eliminated. Unfortunately, they do occur. To protect a circuit against these destructive currents, a protective device must determine when a fault condition develops and automatically disconnect the electrical equipment from the power source. A fuse is the simplest device for interrupting a circuit experiencing an overload or a short circuit. Fuse Construction

A typical fuse, like the one shown below, consists of an element electrically connected to ferrules. These ferrules may also have attached end blades.The element provides a current path through the fuse. It is enclosed in a tube, and surrounded by a filler material. Tube Element

Ferrule

Filler Material

End Blade

17

Closed Switch Symbol

As mentioned earlier, switches are normally shown in their “Off” or “Open” position. For the purpose of illustration, the following symbol can be used to show a switch closed, connecting the load to the power source. This is not a legitimate symbol. It is used here for illustrative purposes only.

Using a Fuse in a Circuit

In the following example a motor is connected to a voltage source through a fusible safety switch. The switch and fuse function as part of the conductor supplying power to the motor.

Fuse Subject to Overcurrent

Current flowing through the fuse element generates heat, which is absorbed and dissipated by the filler material. When an overcurrent occurs, temperature in the element rises. In the event of a transient overload condition the excess heat is absorbed by the filler material. However, if a sustained overload occurs, the heat will eventually melt open an element segment. This will stop the flow of current.

18

Fuse Clearing Time

Fuses have an inverse time-current characteristic. The greater the overcurrent, the less time it takes for the fuse to open. This is referred to as the clearing time of the fuse. Clearing Time of Fuse

Time

Less Current - More Time

More Current - Less Time

Current

Open Fuse Symbol

For the purpose of explanation the following symbol is used to show an open fuse. This is not a legitimate symbol. It is used here for illustrative purposes only.

Overload Current

Returning to the example of a motor circuit, if an overload occurs, temperature will rise in the fuse, eventually causing it to open. Power will be removed from the motor, which will coast to a stop.

19

Short-Circuit Current

Short-circuit current can be several thousand amperes, and generates extreme heat. When a short circuit occurs several element segments can melt simultaneously, which helps remove the load from the power source quickly. Short-circuit current is typically cut off in less than half a cycle, before it can reach its full value.

Nontime-Delay Fuses

Nontime-delay fuses provide excellent short circuit protection. However, short-term overloads, such as motor starting current, may cause nuisance openings of nontime-delay fuses. For this reason, they are best used in circuits not subject to large transient surge currents. Nontime-delay fuses usually hold 500% of their rating for approximately one-fourth of a second, after which the current-carrying element melts. This means that these fuses should not be used in motor circuits, which often have starting currents greater than 500%.

Time-Delay Fuses

Time-delay fuses provide both overload and short-circuit protection. Time-delay fuses usually allow five times the rated current for up to ten seconds. This is normally sufficient time to allow a motor to start without nuisance opening of the fuse. However, if an overload condition occurs and persists, the fuse will open.

20

Fuse Ratings And Classifications

Ampere Rating

Each fuse has a specific ampere rating, which is its continuous current-carrying capability. The ampere rating of the fuse chosen for a circuit usually should not exceed the current-carrying capacity of the circuit. For example, if a circuit’s conductors are rated for 10 amperes, the largest fuse that should be selected is 10 amperes. However, there are circumstances where the ampere rating is permitted to be greater than the current-carrying capacity of the circuit. For example, motor and welder circuits’ fuse ratings can exceed conductor ampacity to allow for inrush currents and duty cycles within limits established by the NEC®.

Voltage Rating

The voltage rating of a fuse must be at least equal to the circuit voltage. The voltage rating of a fuse can be higher than the circuit voltage, but never lower. A 600 volt fuse, for example, could be used in a 480 volt circuit, but a 250 volt fuse could not be used in a 480 volt circuit.

Ampere Interrupting Capacity (AIC)

Fuses are also rated according to the level of fault current they can interrupt. This is referred to as ampere interrupting capacity (AIC). A fuse for a specific application should be selected so that it can sustain the largest potential short circuit current that could occur in the application. Otherwise, the fuse could rupture, causing extensive damage, if the fault current exceeded the interrupting ability of the fuse.

21

UL Fuse Classification

Fuses are grouped into current limiting and non-current limiting classes based on their operating and construction characteristics. Fuses that incorporate features or dimensions for the rejection of another fuse of the same ampere rating, but with a lower interruption rating, are considered current limiting fuses. Underwriters Laboratories (UL) establishes and standardizes basic performance and physical specifications in developing its safety test procedures. These specifications have resulted in distinct classes of low voltage fuses (600 volts or less). The following chart lists various UL fuse classes. Fuse Ratings Class

Amps

Volts

Dimensions

Int. Ratings

I²t, Ip

Circuits

H

1-600A

250 and 600V

NEC standards

10,000A —

Less than 10,000A

General purpose circuits

K5*

1-600A

250 and 600V or less AC

Class H without rejection

100,000A

I²t - RK5 up to 100A Ip - RK5 up to 100A

Feeder circuits

Diff. From Class H

200,000A

I²t - Low Ip - Low

Main & feeder circuits

J

1-600A 600V or less

RK1

1/10600A

Class H 600V or less 250 V or less with rejection feature

200,000A

I²t - Slightly>J Main & feeder Ip - Slightly>J circuits (motor load small percent)

RK5 (time delay)

1/10600A

Class H 600V or less 250 V or less with rejection feature

200,000A

I²t ->RK-1 Ip -RK-1

Motor starting currents

T

1-1200A

300V AC

Diff. From Class H

200,000A

I²t - <J Ip - <J


T

1-800A

600V AC

Diff. From Class H

200,000A

I²t - =J Ip - =J


L

601- 600V or less 6000A

Bolt type

200,000A

I²t - Low Ip - Low


* Class K5 fuses do not prohibit the use of Class H type fuses in a switch.

22

Class R Current Limiting Fuses

The following illustration shows Class R type fuse holders, which feature rejection clips or pins that permit only Class R fuses to be installed. This prevents installation of a fuse with a lower AIC rating, such as a Class H or K.

Groove

Rejection Clip

Notch

Pin

Ferrule Type (60 A Max)

Blade Type (61 - 600 A)

Review 2 1.

Fuses have an ____________ time-current characteristic.

2.

A fuse can usually interrupt short-circuit current in less than ____________ a cycle.

3.

Nontime-delay fuses provide excellent ____________ circuit protection.

4.

____________ - ____________ fuses provide overload and short circuit protection.

5.

The continuous current carrying capability of a fuse is known as its ____________ rating.

6.

The voltage rating of a fuse can be ____________ than the circuit voltage, but never ____________ .

7.

The interrupting rating of a Class R fuse is ____________ amperes.

23

Enclosures

The National Electrical Code® defines an enclosure as the case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts, or to protect the equipment from physical damage (Article 100 - definitions). The NEC® definition references ANSI/NEMA standard 250. The standard for enclosures of electrical equipment is UL 50, published by Underwriters Laboratories (UL). The standard provides enclosure descriptions, features, and test criteria for hazardous (classified) and nonhazardous locations. The following brief descriptions cover enclosures available for Siemens safety switches. Type 1 Enclosures

Type 1 enclosures are intended for indoor use primarily to provide protection against limited amounts of falling dirt and contact with the enclosed equipment in locations where unusual service conditions do not exist.

Type 1 Enclosure

24


Type 3R Enclosures

Type 3R enclosures are intended for outdoor use primarily to provide a degree of protection against falling rain and sleet and protection from contact with the enclosed equipment. They are not intended to provide protection against conditions such as dust, internal condensation, or internal icing.

Type 3R Enclosure

25

Type 4 and 4X Enclosures

Type 4 enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust, rain, splashing water, hose-directed water, and damage from external ice formations. They are not intended to provide protection against conditions such as internal condensation or internal icing. Type 4X enclosures are made of a material such as stainless steel and provide a high degree of protection against corrosion. Type 4X stainless steel enclosures are also available with a window to allow viewing of the visible blade position for switches with 30 - 400A ratings. The window also allows viewing of indicating fuses in 30 - 200A fusible switches.

Type 4

26

Type 4X Stainless

Type 4X Stainless with Viewing Window

Non-Metallic 4X Enclosure

A fiberglass-reinforced polyester version of the 4X enclosure is also available. This Non-Metallic 4X enclosure has no external metal parts. It also features external mounting, a cover interlock, and a removable door for easier wiring.

Type 4X Non-Metallic

27

Type 3S and 12 Enclosures

Type 3S enclosures are suitable for use in outdoor locations which require a degree of protection against windblown dust. They are intended to allow operation when ice laden, but are not intended to protect against condensation or internal icing. Type 12 enclosures provide a degree of protection against dust, falling dirt, and dripping water in indoor locations, but are not intended to protect against conditions such as internal condensation. Type 12 enclosures are also available with a window to allow viewing of the visible blade position for switches with 30 - 600A ratings and viewing of indicating fuses in 30 - 200A fusible switches.

Type 3S / 12 Enclosure

28

Type 3S / 12 Enclosure with Viewing Window

Type 7 and 9 Enclosures

Type 7 and 9 enclosures. Type 7 enclosures are intended for indoor use in locations classified as Class I, Groups A, B, C, or D, as defined in the NEC®. Type 9 enclosures are intended for indoor use in locations classified as Class II, Groups E, F, or G, as defined in the NEC®.

Type 7 and 9 Enclosure

Hazardous Environments

Articles 500 through 504 of the National Electrical Code® cover the use of electrical equipment in locations where fire or explosions due to gas, flammable liquids, combustible dust, or ignitible fibers may be possible. While you should never specify a hazardous location, it is important to understand the regulations that apply. It is the user’s responsibility to contact local regulatory agencies to define the location as Division I or II and to comply with all applicable codes.

29

Divisions

Division I refers to a situation where hazardous materials are normally present in the atmosphere. Division II identifies conditions where the atmosphere may become hazardous as a result of abnormal conditions. For example, if a pipe carrying a hazardous material developed a leak, the surrounding atmosphere could become hazardous.

Classes and Groups

Hazardous locations are further identified by class and group. Class I, Groups A, B, C, and D are chemical gases or liquids. Class II, Groups E, F, and G include flammable dust. Class III includes all ignitible fibers and lints such as clothing fiber in textile mills. Class III is not divided into groups. Group

Class I

Group

Hubs

Acetylene

Class III Ignitable Fibers

E

Metallic Dust

na

Rayon

na

Jute

B

Hydrogen

F

Carbon Dust

C

Acetaldehyde Ethylene Methyl Ether

G

Grain Dust

D

Acetone Gasoline Methanol Propane

Various hubs are available for attaching cable conduit to the enclosures.

HV300 3” Conduit Hub Type 3R Enclosure

30

Group

Groups E-G Flammable Dust

Groups A-D Gases and Liquids A

Class II

HS200 2” Conduit Hub Type 3R Enclosure

SSH 150 1-1/2” Conduit Hub Type 4 / 4X Enclosure

Switch Design

The enclosure houses the switch mechanism, wire connectors, and an operating mechanism. A handle, connected to the operating mechanism, opens and closes the visible blade contacts. If the switch is fusible the enclosure also houses the fuse clips. Provisions have been made for locking the door and/ or switch handle.

Visible Blade Switch Contacts

Operating Mechanism

Defeatable Cover Interlock

Operating Handle

Fuse Clips

Door Latch with Padlock Provision

Door

Wire Connectors

31

Knife Blade Switch Principle

Switches use contacts to break the circuit and stop the flow of current. A typical switch assembly consists of a stationary contact, a hinged movable contact, and an operating handle. The hinged movable contact may also be referred to as a knife blade. If the movable contact is not touching the stationary contact, no current flows.

From Power Supply Stationary Contact Movable Contact

To Load

Moving the handle to the “On” position closes the contacts and provides a complete path for current to flow from the power supply to the load.

From Power Supply

To Load

32

Moving the handle to the “Off” position opens the contacts, interrupting the flow of electricity. As the contacts start to open, current continues to flow across the air gap between the two contacts in the form of an arc. Current continues to flow until the physical distance between the contacts is great enough to interrupt the flow of current.

From Power Supply

“Electrical Hinge”

To Load

The point at which the arc is extinguished is called the break distance.

From Power Supply Break Distance

To Load

33

VBII Safety Switch Design

Unlike the knife-blade switch, the switching action of the Siemens 30-200A VBII Safety Switch breaks the arc in two places. As a result, two smaller arcs are created, and heat generation is reduced. The switching speed is also increased, since the breaking distance is effectively doubled. The overall result is enhanced performance and increased longevity. Also, in contrast to the knife blade switch, the VBII Safety Switch blades are self-aligning, ensuring positive contact. Furthermore, the “electrical hinge,” a wear and friction point, has been eliminated. The result is a fast, positive, and reliable switching action.

Closed

In Operation

Open

VBII Switch Action

34

“Over-Center-Toggle” Switch Action

Another feature which enhances the speed of switching is the “over-center-toggle” design. During operation of the switch, for example, from the “Off” position to the “On,” as the handle is moved up the switching action does not occur gradually. As the handle is moved past the midpoint, the switch suddenly and rapidly moves from “Off” to “On.” Besides enhancing the switching speed, this also gives a positive feel to the switch operation.

Switch Off

In Operation

Switch On

VBII “Over-Center-Toggle” Action

35

Defeatable Cover Interlock

36

The VBII cover interlock prevents opening the door while the switch is in the “On” position. Normally, it also prevents turning the switch “On” with the door open. However for the purposes of testing or servicing, the door interlock is defeatable. As in the following illustration, this can be done with an ordinary screwdriver.

Review 3 1. Type ____________ enclosures are intended for indoor use primarily to provide protection against contact with the enclosed equipment in locations where unusual service conditions do not exist. 2.

Type ____________ enclosures are intended for outdoor use primarily to provide a degree of protection against falling rain and sleet.

3.

Switches use ____________ to break the circuit and stop the flow of energy.

4.

The VBII 30-200 A switch design breaks the arc in ____ ________ places, thereby reducing heat and switching time.

37

Safety Switch Ratings

Ampere Rating

Siemens safety switches are available in two types: general duty and heavy duty, both of which are listed by Underwriters Laboratories (UL). Every safety switch has a specific ampere rating, which is the maximum continuous current it can carry without causing deterioration or exceeding temperature rise limits. General duty switches are available with ampere ratings of 30, 60, 100, 200, 400, and 600 amperes. Heavy duty switches are rated for 30, 60, 100, 200, 400, 600, 800, and 1200 amperes. (Though not discussed in this course, bolted pressure switches are also available, with ampere ratings of 800, 1200, 1600, 2000, 2500, 3000, and 4000 amperes.) Amps 4000 3000 2500 2000 1600 1200 800 600 400 200 100 60

S G eneral

Duty

30

General Duty

38

Heavy Duty

Bolted Pressure

Short Circuit Withstandability

Safety switches must be capable of withstanding the largest potential short circuit current that can occur in the selected application. General duty switches have a maximum short circuit withstandability of 100,000 amperes, while the equivalent rating of heavy duty switches is 200,000 amperes.

Voltage Rating

Safety switches are also rated according to the maximum voltage they can handle. The voltage rating of the switch must be at least equal to the circuit voltage. In other words, it can be higher than the circuit voltage, but never lower. For example, a safety switch rated for 600 volts can be used on a 480 volt circuit, but a switch rated for 240 volts must not be used on a 480 volt circuit. The following chart reflects available voltage ratings.

S G ener

al Duty

General Duty

Heavy Duty

Bolted Pressure

240 VAC 250 VDC

240 VAC 600 VAC 600 VDC

240 VAC 480 VAC 600 VAC* *600 VAC Bolted Pressure Switch in not UL Listed

39

Dual Horsepower Ratings

All Siemens safety switches have two horsepower ratings for motor applications. This is referred to as “dual horsepower rated.” For example, a switch might have a standard rating of 10 HP, and a maximum rating of 30 HP. The standard rating, 10 HP, applies when non-time delay fuses are used. Non-Time Delay Fuse Use Standard HP Rating

Fusible Enclosed Switch

The maximum rating of 30 HP applies when time delay fuses are used. Time Delay Fuse Use Maximum HP Rating

Fusible Enclosed Switch

The following chart reflects the range of horsepower ratings for Siemens safety switches. Safety Switch Type General Duty

Heavy Duty

40

Voltage

Horsepower Range

240 VAC

1½ - 200

250 VDC

5-50

240 VAC

1½ - 250

600 VAC

3-500

250 VDC

5-50

600 VDC

15-50

Switch Circuit Types And Terminology

Pole

The term pole refers to the number of wires that a switch will disconnect at one time. The following drawing, for example, shows a 3-pole safety switch. The three circuits are mechanically connected so that all three poles connect and disconnect the line and load simultaneously when the switch is operated. In this case, each pole is fused for overcurrent protection.

Fuse

3-Pole, 3-Fuse

41

Circuit Configurations

Following are circuit configuration diagrams for 2- and 3-pole safety switches. Safety switches may be fusible, non-fusible, or fusible with a solid neutral. Fusible

Non-Fusible

Solid Neutral

2-Pole

2-Pole, 2-Wire

2-Pole, 3-Wire

Solid Neutral

3-Pole

3-Pole, 3-Wire

3-Pole, 4-Wire

The following circuit configurations are available in Siemens safety switches: 2-Pole 3-Pole 6-Pole (not shown) 2-Pole, 2-Wire 3-Pole, 3-Wire 4-Pole, 4-Wire (not shown) 6-Pole, 6-Wire (not shown) 2-Pole, 3-Wire 3-Pole, 4-Wire

42

Example

The circuit configuration required depends on the load and on the power supply connected to it. For example, a three-phase motor needs a 3-pole switch to connect it to a three-phase power supply. If overcurrent protection is required, a fusible 3-pole safety switch should be selected, as in the following example. 3Ø AC Power Supply

3Ø Motor

43

Switch Throws

All the example switches shown so far have been single throw. “Throw” is the term used to refer to the number of different positions a switch has, that is, the number of different circuits it can connect a given wire to. Switches may be single throw, double throw, or multiple throw. The simplest is a single pole, single throw:

Next in complexity is the single pole, double throw which can connect a single wire to one of two different circuits:

Two- and three-pole single throw switches have already been shown. The double pole, double throw (DPDT) switch can connect each of two different wires to two different circuits:

Many different arrangements are possible. The following illustrates only a few of them:

DPDT

44

DP3T

3P3T

Catalog Numbers

To help identify each type of safety switch, a catalog number is assigned. The catalog number provides a description of the safety switch. There are eight parts to the catalog number of Siemens VBII Safety Switches. The following figure illustrates a typical catalog number. Catalog Number Part 1 Part 2 Part 3 Part 4 Part 5 Part 6 Part 7 Part 8 HF364NRCU=

Part 1

H

F

3

6

4

N

R

CU

Part 1 indicates the switch type. There are three types available: General Duty 10k AIC Max. (Plug Fused & 60A Max Non-Fused); General Duty; and Heavy Duty. Designator

Switch Type

L

General Duty 10k AIC Max

G

General Duty

H

Heavy Duty

DT

Heavy Duty Double Throw

DTG

General Duty Double Throw

From the above table, one can see that the example switch, type H, is a heavy duty switch. Part 2

Part 2 indicates whether the switch is fused or non-fused. “F” designates a fused switch; while “NF” designates non-fused types. The example switch is fused.

45

Part 3

Part 3 of the catalog number indicates the number of poles. Siemens VBII safety switches can be provided with 1, 2, or 3 poles. (A neutral, if required, is not included in the number of poles.) The following shows a 3-pole safety switch used with a 3-phase AC motor. The example catalog number calls for a 3pole safety switch. Three-Phase Supply Power

3-Pole Enclosed Switch

Motor

Part 4

Part 5

Part 4 of the catalog number indicates the voltage rating. The example catalog number indicates a safety switch with a maximum voltage rating of 600 volts. Designator

Voltage

1

120V or 120/240V

2

240V

6

600V

Part 5 of the catalog number refers to the switch’s current rating. The example indicates a safety switch with a 200 ampere rating. Designator Amperes

46

1

30A

2

60A

3

100A

4

200A

5

400A

6

600A

7

800A

8

1200A

Part 6

Part 6 of the catalog number indicates whether or not a neutral is included with the switch. If no neutral is needed, part 6 of the catalog number is simply omitted. If a neutral is needed, an “N” is added to the catalog number, as in the example.

Part 7

Part 7 of the catalog number indicates the type of enclosure. The example catalog number indicates a safety switch in a NEMA Type 3R outdoor enclosure.

Part 8

Designator

Enclosure Type

Omit

Type1, Indoor

R

Type 3R, Outdoor

S

Type 4/4X, Stainless Steel

X

Type 4/4X, Non-Metallic

J

Type 12, Industrial

Part 8 of the catalog number is for special applications. The following table lists the possible applications. For example, “CU” indicates factory-installed copper wire grips, as in the representative catalog number given above. Designator

Special Applications With:

CH

Crouse-Hinds Receptacle

CJ

Factory J Fuse Spacings

CR

Class R Clips Installed

CU

Copper Wire Grips Installed

G

Factory-Installed Ground Bar

PN

Pyle-National Receptacle

W

Viewing Window

47

Review 4 1.

The ____________ rating is the maximum continuous current a safety switch can carry.

2.

The maximum short circuit current withstandability of heavy duty switches is ____________ amperes.

3.

The maximum horsepower available in a 240 VAC general duty safety switch is____________ HP.

4.

A ____________ describes the number of isolated circuits that can pass through the safety switch at one time.

5.

The number “3” in part five of the heavy duty catalog number indicates ____________ . a. c.

3-pole 100 amperes

b. d.

3R enclosure 600 VAC

6. ____________ refers to the number of different positions of a given switch.

48

General Duty Safety Switches

General duty switches are intended for use primarily on power supplies rated at 240 VAC or less, where the available fault current is less than 100,000 amperes (with Class R or T fuses, or 10,000 A max with Class H fuses). They can be supplied in a Type 1(indoor) or Type 3R (outdoor) enclosure. Plug Fuse Type Safety Switch

The general duty plug fuse type switch is available for 120 or 240 volt systems. It is suitable for one- or two-pole applications, and is rated at 30 amperes. A separately supplied, 30-ampere Type S plug fuse is required. This switch is available for use on two-wire or three-wire motor applications up to three horsepower. A non-fusible model comes in a two-pole configuration. It is rated at 60 amperes, and can be used with motors up to 10 HP. There are also pullout models available in fused and non-fused versions.

General Duty Switches

The fusible general-duty safety switch is available in two and three poles, both with solid neutral, or with four poles. The non-fusible model is available with a two- or three-pole configuration. Fusible switches accept Class H fuses as standard. A field-installable rejection kit is available which rejects all but Class R fuses. All general duty switches have both cover and handle padlocking capabilities.

Ratings

Ampere ratings: 30, 60, 100, 200, 400, or 600 amperes Fuses: 1 - 600 ampere Class H, K, or R 70 - 600 ampere Class T cartridge fuse Voltage ratings: 240 VAC, 250 VDC Max short-circuit current withstandability: 100,000 amperes (with current limiting fuses)

49

Type 1 Enclosure

General duty switches are available in the NEMA Type 1 enclosure, which is intended for indoor use. An interlock prevents the cover from being opened when the switch is in the “On” position. A cover interlock also prevents turning the switch “On” with the door open. (There is a front operable release for this feature.) This enclosure is intended primarily to provide protection against contact with the safety switch, and is used in locations where unusual service conditions do not exist.

S G en er

al D ut y

General Duty Safety Switch Type 1 Enclosure

50

Type 3R Enclosure

General duty 2- and 3-pole safety switches are also supplied in a Type 3R enclosure, which is intended for outdoor use, and provides a degree of protection against falling rain and sleet. It is also able to withstand the formation of ice on the enclosure without damage, but is not intended to provide protection against conditions such as dust, internal condensation, or internal icing.

S G en er

al D ut y

General Duty Safety Switch Type 3R Enclosure

51

Heavy Duty Safety Switches

Type 1 Enclosure

Heavy duty safety switches can be used on power supplies up to 600 Volts, AC or DC. They can be used in applications where the available fault current is 200,000 amperes or less. A cover interlock prevents inadvertant opening of the cover while the switch is in the “On” position, and a mechanism interlock prevents inadvertant turning on of the switch while the cover is open. Heavy duty safety switches also have cover and handle padlocking capabilities.

Type 1 Enclosure

52

Enclosures for Heavy Duty Safety Switches

Heavy duty safety switches can also be supplied with Type 3R, 4 / 4X, and 12 enclosures.

Type 12 Type 4X Stainless

Type 3R

Ratings

Current ratings: 30, 60,100,200, 400, 600, 800, & 1200 amperes Fuses: 1 - 600 ampere Class H, J, K, and R cartridge fuses 1 - 1200 ampere Class T cartridge fuses 601-1200 ampere Class L bolt-in fuses (Fusible 800 and 1200 A switches have Class L fuse provisions as standard) Voltage ratings: 240 /480/ 600 VAC; 250 / 600 VDC Max short-circuit current withstandability: 200,000 amperes

53

Interlock Receptacle

The interlock receptacle safety switch provides cord connection for heavy-duty portable equipment such as refrigerated trucks, welders, and other portable electric tools. It is fitted with a Crouse-Hinds Arktite®or similar receptacle.This receptacle is interlocked to prevent insertion or removal of the plug if the switch is in the “On” position. The Crouse-Hinds receptacle switch requires a Crouse-Hinds 4-wire, 3-pole, style 2, grounded APJ plug. The interlock receptacle safety switches are rated for 30, 60, and 100 amperes. The enclosure meets the requirements for Type 4, 4X, or 12/3R enclosures.

Receptacle

Arktite® is a registered trademark of the Crouse-Hinds Company.

54

Four- and Six-Pole Safety Switches

Four- and six-pole heavy-duty safety switches are available in current ratings of 30 - 200 amperes, in Type 1 / 3R / 12 or Type 4 / 4X enclosures, fusible or non-fusible. These switches are commonly used as a disconnecting means for two-speed, two-winding motors. A 4-pole switch is also used in 3-phase, 4-wire circuits when a switching neutral is required.

Double Throw Switches

Double throw switches are used to transfer loads from one power source to another. For example, a critical piece of equipment often needs a back-up power supply in case the main power supply fails or needs maintenance. Double throw switches are also used to connect a single power source to either of two loads. 30-600A double-throw fusible switches are available in Types 1 and 3R enclosures, while non-fusible models are available in Types 1 and 3R for 30 to 1200A, and in 4 / 4X and 12 for 30 to 200A. Double throw switches are rated for 240 VAC/250 VDC or 600 VAC.

55

Double Throw Switch Application

A motor, for example, can be connected through a double throw switch to power supply A or power supply B. When the handle is in the center position the switch is “Off” and no power flows to the motor. From Power Supply A

Handle Center

Motor

From Power Supply B

Moving the handle to the up position connects the motor to power supply A. From Power Supply A

Handle Up

Motor

From Power Supply B

Moving the handle to the down position connects the motor to power supply B. From Power Supply A

Handle Down

Motor

From Power Supply B

56

Safety Switch Accessories

A full range of accessories is available for Siemens VBII Safety Switches. Some of these are shown below. Both General Duty and Heavy Duty Switches are fieldconvertible to accept Class J or Class T fuses.

HT63 Class T Fuse Adapter Kit

Standard Neutral Kits can be field installed in both General and Heavy Duty Safety Switches, and UL listed 200% Neutrals are available on 100-600A Heavy Duty Switches.

HN612 Neutral Kit

HN264 200% Neutral Kit

The Multiple Padlock Accessory is a tamper-proof device to provide for multiple padlocking to meet OSHA or plant requirements.

SL0420 Multiple Padlock Accessory

57

The following illustrates some of the other accessories available for General and Heavy Duty Safety Switches. Copper Lug Kits

Auxiliary Contacts

HLC612 HA161234 Isolated Ground Kits

Fuse Puller Kits HG261234

HP61

Standard Ground Kits

HG61234 Class R Fuse Clip Kits

HR612

Heavy Duty Switches are UL approved to accept field installed Copper Lug Kits. Equipment Ground Kits are available for all General Duty and Heavy Duty Switches. They come standard in Type 4 / 4X and Type 12 Switches, and are field installable in Type 1 and Type 3R. Isolated Ground Kits are also available for 30-600A Heavy Duty Switches. Some circuits with a high degree of computer or other electronic loading require an isolated ground to prevent interference from the building ground and neutral lines.

58

Auxiliary Contacts are available only for Heavy Duty Switches. They come with 1 normally open and 1 normally closed or 2 normally open and 2 normally closed contacts. A PLC Auxiliary Switch for 30-200A switches is also available. It has very low contact resistance, which is compatible with the low voltages and currents typically found in PLC circuits.

HA261234 Auxiliary Contract Kit

Fuse Puller Kits are field installable in 30-100A Heavy Duty Switches.

HP61 Fuse Puller Kit

Class R Fuse Clips are used to prevent the installation of noncurrent-limiting Class H or Class K fuses. All General and 30-600A Heavy Duty Switches are field convertible to accept Class R Fuse Clip Kits.

HR612 Class R Fuse Clips

59

Review 5

60

1.

The maximum short circuit current withstandability of general duty switches is ____________ amperes.

2.

The maximum short circuit current withstandability of heavy duty switches is ____________ amperes.

3.

The maximum current rating of a VBII heavy duty switch that is not a bolted pressure switch is ____________ amperes.

4.

The ____________ ____________ safety switch provides cord connection for heavy duty portable equipment.

5.

____________ ____________ switches are intended to transfer loads from one power source to another.

Selecting Safety Switches

While selecting a safety switch is not difficult, flow charts can help to make it even easier. The following flow chart can be used to make key decisions in the selection of a safety switch. Start

Is Circuit Protection Required?

No

Yes

Select Fusible Switch

Select Non-Fusible Switch

No

Data Needed: 1) System Voltage 2) Full-Load Amps Of Utilization Device 3) Number Of Poles (Solid Neutral?) 4) Environment

Is It A Motor Circuit?

Yes

Data Needed: 1) System Voltage 2) Motor Horsepower 3) Number Of Poles (Solid Neutral?) 4) Environment

No

Fuse Data Needed: 1) Available Fault Current 2) System Voltage 3) Full-Load Amps Of Utilization Device 4) Fuse Class 5) Number Of Fuses Switch Data Needed: 1) Available Fault Current 2) System Voltage 3) Full-Load Amps Of Utilization Device 4) Number Of Poles (Solid Neutral?) 5) Fuse Class 6) Environment


Yes

Fuse Data Needed: 1) Available Fault Current 2) System Voltage 3) Full-Load Amps Of Motor 4) Fuse Class 5) Number Of Fuses Switch Data Needed: 1) Available Fault Current 2) System Voltage 3) Motor Horsepower 4) Number Of Poles (Solid Neutral?) 5) Fuse Class 6) Environment

61

Selecting a Non-Fusible Switch

The first question is: Is circuit protection required? If circuit protection is not required a non-fusible switch would be selected. Start

No



Non-Fusible Switch not Used on a Motor Circuit

Yes


If a non-fusible switch is selected, the next question is: Is it a motor circuit? If the switch is not used on a motor circuit the following information must be known: 1) System voltage:

120 VAC, 240 VAC, 480 VAC, 600 VAC, 250 VDC, 600 VDC 2) Full-load amperes of the device to be used on the switch 3) The number of poles required, and if a neutral is needed 4) The environment (enclosure type) Select Non-Fusible Switch

No


62


Non-Fusible Switch Used on a Motor Circuit

If the switch is used on a motor circuit, the same data is a required, except that motor horsepower replaces full-load current. 1) System voltage 2) Motor horsepower 3) The number of poles required, and if a neutral is needed 4) The environment (enclosure type) Select Non-Fusible Switch

No



Selecting a Fusible Switch

Yes

Data Needed: 1) System Voltage 2) Motor Horsepower 3) Number Of Poles (Solid Neutral?) 4) Environment

If circuit protection is required, a fusible switch would be selected. Start

No



Yes


63

Fusible Switch not Used on a Motor Circuit

If a fusible switch is selected, the next question is: Is it a motor circuit? If not, the following information must be known to select a fuse: 1) Available fault current 2) System voltage 3) Full-load amperes of the device to be used on the switch 4) Fuse class 5) Number of lines to be fused The following must be known to select a switch: 1) Available fault current 2) System voltage 3) Full-load amperes of the device to be used on the switch 4) Number of poles, and if a neutral is needed 5) Fuse class 6) Environment (enclosure type) Select Fusible Switch

No


64


Fusible Switch Used on a Motor Circuit

If the switch is used on a motor circuit, the following information must be known to select a fuse: 1) Available fault current 2) System voltage 3) Full-load amperes required by the motor 4) Fuse class 5) Number of lines to be fused The following must be known to select a switch: 1) Available fault current 2) System voltage 3) Motor horsepower 4) Number of poles, and if a neutral is needed 5) Fuse class 6) Environment (enclosure type) Select Fusible Switch

No



Yes

Fuse Data Needed: 1) Available Fault Current 2) System Voltage 3) Full-Load Amps Of Motor 4) Fuse Class 5) Number Of Fuses Switch Data Needed: 1) Available Fault Current 2) System Voltage 3) Motor Horsepower 4) Number Of Poles (Solid Neutral?) 5) Fuse Class 6) Environment

65

Example of Selecting a Non-Fusible Safety Switch

In the following example, a safety switch needs to be provided for an application that does not require circuit protection. The full-load current of the utilization device is 45 amperes. It is not a motor. The system voltage is 240 VAC, 3phase, 3-wire (without neutral). The environment is indoors, and there are no unusual conditions such as dust or liquids. Recall from earlier discussion that in general, all conductors (including the switch) must be capable of carrying 125% of the full-load current. The full-load current of the utilization device is 45 amperes; a switch must be selected that can carry 56 amperes. 45 amperes X 125% 56 amperes

Knowing that the switch will be used indoors, with no unusual conditions, a Type 1 enclosure can be selected. The other requirements can be met with a general duty switch. Referring to the General Duty Safety Switches section of the Speedfax catalog, the first 240 volt, 3-pole, non-fusible switch that will handle 56 amperes is a 60 amp switch. The catalog number is GNF322. Since the required fuse is a Class R, and the circuit has a potential fault current of 200,000 amperes, a class R fuse kit (catalog number HR64) is required. This can be found in the accessory section of the Speedfax. Indoor - Type 1 System

Ampere Catalog List Ship Wt. Catalog Rating Number Price $ Std. Pkg. Number

240 Volt Non-Fusible 2-Pole or 3-Pole 30 GNF321 60 GNF322 100 GNF323 200 GNF324 400 GNF325 600 GNF326

Example of Selecting a

66

Outdoor - Type 3R List Ship Wt. Price $ Std. Pkg.

GNF321R GNF322R GNF323R GNF324R Use 600V Switch - HF365R Use 600V Switch - HF366R

In the following example a safety switch needs to be


provided for an application that does require circuit protection. This application will have a 480 VAC, three-phase, 75 HP motor, not needing a neutral connection. The customer has specified an RK5 time-delay fuse, for a potential fault current of 200,000 amperes. The switch will be located indoors with no unusual service conditions. The 480 VAC requirement dictates a heavy duty, 600 volt, fusible switch. Turning to the appropriate Speedfax page, the enclosure type is located, that is, Indoor — Type 1. Next, the 600 Volt Fusible, 3-pole, 3-fuse table is found. From the horsepower ratings, in the 480 VAC, 3-phase, 3-wire section, a switch will be selected from the maximum (Max.) column. The maximum column is chosen because the customer selected time delay fuses. (Had non-time delay fuses been specified, the standard horsepower column would be used.) Reading down the maximum horsepower column, 125 HP, the first rating meeting the 75 HP requirement, is found. Reading to the left the catalog number, HF364, is found under Type 1. (It can also be seen that this safety switch is rated for 200 amperes.) Since the required fuse is a Class R, and the circuit has a potential fault current of 200,000 amperes, a Class R fuse clip kit (catalog number HR64) is also required. This can be found in the accessory section of the Speedfax. Horsepower Ratings 480 VAC 1 Phase, 3 Phase, Ship Wt. 2 Wire Ampere Catalog List 3 Wire System Rating Number Price $ Std. Pkg. Std. Max. Std. Max. Indoor - Type 1

600 Volt Fusible 3-Pole, 3-Fuse 30 60 100 200 400 600 800 1200

HF361 HF362 HF363 HF364 HF365 HF366 HF367 HF368

3 5 10 25

7½ 20 30 50

5 15 25 50 100 150 200 200

15 30 60 125 250 400 500 500

67

Selecting a Fuse

Section 430.6 of the NEC® requires that where the current rating of a motor is used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit overcurrent devices, etc., the values given in Tables 430.247 through 430.250 are required to be used instead of the actual motor nameplate current rating. In order for a customer to properly select a fuse, NEC® Table 430.250 must be referred to. According to NEC® Table 430.250, a 75 HP, 460 VAC motor has a full-load current of 96 amperes. Table 430.250 Full-Load Current,Three-Phase Alternating-Current Motors The following values of full-load currents are typical for motor running at speeds usual for belted motors and motors with normal torque characteristics. Motors built for low speeds (1200 rpm or less) or high torques may require more running current, and multispeed motors will have full-load current varying with speed. In these cases, the nameplate current rating shall be used. The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120, 220 to 240, 440 to 480, and 550 to 600 volts. Induction-Type Squirrel Cage and Wound Rotor (Amperes) Horsepower ½ ¾ 1 1½ 2 3 5 7½ 10 15 20 25 30 40 50 60 75 100 125 150 200 250 300 350 400 450 500

68

115 Volts

200 Volts

208 Volts

230 Volts

460 Volts

575 Volts

2300 Volts

4.4 6.4 8.4 12.0 13.6 -

2.5 3.7 4.8 6.9 7.8 11.0 15.5 25.3 32.2 48.3 62.1 78.2 92 120 150 177 221 285 359 414 552 -

2.4 3.5 4.6 6.6 7.5 10.6 16.7 24.2 30.8 46.2 59.4 74.8 88 114 143 169 211 273 343 396 528 -

2.2 3.2 4.2 6.0 6.8 9.6 15.2 22 28 42 54 68 80 104 130 154 192 248 312 360 480 -

1.1 1.6 2.1 3.0 3.4 4.8 7.6 11 14 21 27 34 40 52 65 77 96 124 156 180 240 302 361 414 477 515 590

0.9 1.3 1.7 2.4 2.7 3.9 6.1 9 11 17 22 27 32 41 52 62 77 99 125 144 192 242 289 336 382 412 472

16 20 26 31 37 49 60 72 83 95 103 118


Table 430.52 of the NEC® is provided to help select a fuse that will not trip while starting a motor, and still provide adequate overcurrent protection. According to this table, the NEC® requires that the ampere rating of an AC motor protected by a time-delay fuse be multiplied by 175%. Table 430.52 Maximum Rating or Setting of Motor BranchCircuit Short-Circuit and Ground-Fault Protective Devices Percentage of Full-Load Current

Type of Motor Single-phase motors

Nontime Delay Fuse

Dual Element (TimeDelay) Fuse

Instantaneous Trip Breaker

Inverse Time Breaker

300

175

800

250

800

250

AC polyphase motors other than wound-rotor Squirrel cage 300 175 - other than Design E or Design B energy efficient Design E or Design B energy efficient

300

175

1100

250

Synchronous

300

175

800

250

Wound rotor

150

150

800

150

Direct current (constant voltage)

150

150

250

150

Multiplying the motor rating of 96 amperes times 175% results in a fuse size of 168 amperes. Since this is a non-standard fuse size, the next standard fuse size of 175 amperes would be selected. 96 amperes X 175% 168 amperes

Full-Load Motor Current NEC® Requirement Fuse Rating

69

Review 6

70

1.

A ____________ safety switch would be selected when circuit protection is not required.

2.

A ____________ safety switch would be selected when circuit protection is required.

3.

When selecting a non-fusible safety switch for utilization device rated at 100 amperes, a switch must be selected that can carry ____________ amperes.

4.

According to the NEC®, the ampere rating of an AC motor protected by a time-delay fuse should be multiplied by ____________ %.

Review Answers

Review 1

1) fusible; 2) 50; 3) a; 4) overload, short circuit; 5) short circuit; 6) overload; 7) peak let-thru; 8) energy; 9) 240; 10) 310.16; 11) 125.

Review 2

1) inverse; 2) half; 3) short; 4) Time-delay; 5) ampere; 6) higher, lower; 7) 200,000.

Review 3

1) 1; 2) 3R; 3) contacts; 4) two.

Review 4

1) ampere; 2) 200,000; 3) 200; 4) pole; 5) c; 6) Throw .

Review 5

1) 100,000; 2) 200,000; 3) 1200; 4) interlock receptacle; 5) Double throw.

Review 6

1) non-fusible; 2) fusible; 3) 125; 4) 175.

71

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. Please fill out the answer sheet neatly and completely. After completing the test, mail the answer sheet in for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. 1.

2.

The following symbol represents a non-fusible enclosed switch:

a.

c.

b.

d.

A safety switch combined with fuses in a single enclosure is referred to as a ____________ safety switch. a. b.

3.

heavy duty general duty

10 50

c. d.

25 100

With an increase of current, temperature will ____________ . a. b.

72

c. d.

The National Electrical Code® defines “in sight” as visible and not more than ____________ feet distant. a. b.

4.

non-fusible fusible

increase remain the same

c. d.

decrease increase and decrease

5.

Overcurrent protection is covered by NEC® article ____________ . a. b.

6.

AWG peak current

c. d.

instantaneous current ampacity rating

2 6

c. d.

3 10

Fuses have a/an ____________ time-current characteristic. a. b.

9.

780 240

According to the NEC® a continuous load is a load where the maximum current is expected to continue for ________ ____ hours or more. a. b.

8.

c. d.

The amount of current a conductor can carry on a continuous basis is known as ____________ . a. b.

7.

110 410

direct proportional

c. d.

indirect inverse

Class R fuses have an interrupting rating (AIC) of ________ ____ amperes. a. b.

10,000 50,000

c. d.

100,000 200,000

10. A UL Type ____________ enclosure is intended for indoor use primarily to provide protection against contact with the enclosed equipment in locations where unusual service conditions do not exist. a. b.

1 3R

c. d.

4 12

73

11.

UL Type ____________ enclosures are intended for outdoor use primarily to provide a degree of protection against falling rain and sleet and must remain undamaged by the formation of ice on the enclosure. They are not intended to provide protection against conditions such as dust, internal condensation, or internal icing. a. b.

1 3R

c. d.

4 12

12. The maximum ampere rating of a general duty switch is ____________ amperes. a. b.

200 1200

c. d.

600 4000

13. The maximum ampere rating of a heavy duty switch that is not a bolted pressure switch is ____________ amperes. a. b.

200 1200

c. d.

600 4000

14. Heavy duty switches have a maximum short circuit current withstandability of ____________ amperes. a. b.

10,000 100,000

c. d.

50,000 200,000

15. The maximum horsepower of a 240 VAC heavy duty switch is ___________ HP. a. b.

60 150

c. d.

250 500

16. A catalog number beginning with “GF3” indicates a ______ ______ safety switch. a. b. c. d.

74

general duty, fusible, single pole general duty, fusible, three pole general duty, non-fusible, single pole general duty, non-fusible, three pole

17.

The ____________ safety switch provides cord connection for heavy duty portable equipment. a. b. c. d.

18.

interlocked receptacle double throw bolted pressure plug fuse

Siemens VBII 30 - 200 amp safety switches use a ____________ _____________ switch action. a. b.

Double Break Knife-Blade

c. d.

Stationary Contact Fuse Ejector

19. When selecting a non-fusible switch for use on a nonmotor circuit, which of following information is not needed? a. b.

system voltage full-load amperes

c. d.

fuse class number of poles

20. ____________ safety switches are intended to transfer loads from one power source to another. a. b. c. d.

Interlock receptacle Plug fuse Bolted pressure Double throw

75



76

STEP 2000

Residential Surge Protection

Table of Contents

Introduction ..............................................................................2 Siemens Residential Products ..................................................4 Residential Power Distribution..................................................6 Power Quality ...........................................................................8 Sources of Voltage Surges ...................................................... 13 Surge Protection ..................................................................... 16 Point-of-Entry Surge Protection ..............................................24 Point-of-Use Surge Protection ................................................29 Whole-House Protection.........................................................35 Review Answers.....................................................................43 Final Exam ..............................................................................44

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Residential Surge Protection. Upon completion of Residential Surge Protection, you should be able to:

2

•

Explain the role of surge protectors in the Siemens residential product line

•

Explain the need for surge protection

•

Describe the damaging effects of lightning strikes and other electrical surges to the home distribution system

•

Explain the difference between point-of-use and point-ofentry surge protectors

•

Identify appropriate point-of-use surge protectors for various applications

•

Explain the need for whole-house surge protection and how to achieve it

This knowledge will help you better understand customer applications. In addition, you will be better prepared to discuss electrical products and systems with customers. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. Primax, POWERMAX, and MAX are registered trademarks of Panamax. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-2002, National Electrical Code Copyright, 2001, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories Inc. and UL are registered trademarks of Underwriters Laboratories Inc., Northborook, IL 60062. Other trademarks are the property of their respective owners.

3

Siemens Residential Products

Siemens manufactures a variety of electrical distribution products for residential applications. Load centers and associated circuit breakers supply electrical power throughout the home.

Load Center

GFCI

Surge Protector

AFCI

1-Pole

Triplex

2-Pole Duplex

4

STEP 2000

Load centers and their associated components are covered in the STEP 2000 course titled Load Centers. You should complete the load center course prior to completing Residential Surge Protection. Many of the concepts covered in Load Centers will give you a better understanding of the topics discussed in Residential Surge Protection.

STEP 2000

Load Centers

Surge Protection Products

Load centers and standard circuit breakers cannot protect a home from damaging electrical surges such as those produced by lightning. Siemens manufactures products specifically designed to protect the home from such electrical surges. Siemens electrical surge protection products work in conjunction with load centers and circuit breakers to provide more complete residential circuit protection. Siemens surge protection products are the focus of this course.

5

Residential Power Distribution

Power is generated at a power plant. The most efficient way to transmit this voltage to customers is to increase the voltage. Transmission voltage levels vary, depending on distance and the load it must supply. Transmission voltages are typically 60kV and above. In some cases transmission voltages can be in what is called the extra high voltage range (EHV) of 300 kV and above. Once transmission voltage reaches a local substation it is stepped down to a lower distribution voltage.

Power Supply

6

When the voltage reaches its final destination at a residential customer it is stepped down to 240 volts. The most common supply system used in residential applications today is a singlephase, three-wire supply system. In this system there are 120 volts between either hot wire and neutral and 240 volts between the two hot wires. The 120 volt supply is used for general-purpose receptacles and lighting. The 240 volt supply is used for heating, cooling, cooking, and other high-demand loads.

Service Entrance

Power, purchased from a utility company, enters the house through a metering device and connects to a load center. This is the service entrance. Residential service can come from an overhead utility transformer or from a lateral service run underground.

Distribution

Load centers provide circuit control and overcurrent protection. Power is distributed from the load center to various branch circuits for lighting, appliances, and electrical outlets.

7

Power Quality

Voltage used in the home can be represented by a sine wave. Ideally a sine wave would be smooth and free of disturbances. However, even the best distribution systems are subject to changes in system voltage from time-to-time.

Voltage Variations

Voltage changes can range from small voltage fluctuations of short duration to a complete outage for an extended period of time. Undervoltage occurs when voltage decreases outside normal rated tolerance. An undervoltage is often referred to as a sag when the duration is two seconds or less. Undervoltages and sags can cause a computer to crash and confuse a digital clock. Overvoltages occur when voltage increases above normal rated tolerance. An overvoltage is referred to a swell when the disturbance lasts two seconds or less. Overvoltages and swells can upset sensitive electronic equipment, and cause damage in some cases.

8

Surges

Utility companies strive to maintain uniform voltage but disturbances from outside sources, such as lightning and short circuits, can appear on the sine wave in the form of surges. Surges can range from a few volts to several thousand volts and last from a few microseconds to a few milliseconds. While overvoltage and undervoltage can upset or damage sensitive electronic equipment, surges are far more destructive.

ITI (CBEMA)

Manufacturers of sensitive electronic devices, such as computers, strive to make equipment that will survive fluctuations in the power supply. The Information Technology Industry Council (ITI) was formerly known as the Computer Business Equipment Manufacturers Association (CBEMA). Working with the Department of Commerce, ITI published a set of guidelines for powering and protecting sensitive equipment. As the use of computers has grown, other organizations have made additional recommendations. The Institute of Electrical and Electronic Engineers (IEEE), for example, published engineering guidelines for the selection and application of emergency and standby power systems.

9

ITI (CBEMA) Curve

The ITI (CBEMA) curve was developed to be used as a guideline for manufacturers in designing power supplies for use with sensitive electronic equipment. The vertical axis of the graph is the percent of rated voltage applied to a circuit. The horizontal axis is the time the voltage is applied. Electronic equipment manufactured to these guidelines are expected to survive voltage spikes of short duration. However, voltage spikes that exceed either amplitude or duration of the voltage tolerance envelope will enter the prohibited region. Sensitive electronic equipment can be damaged when voltage spikes are severe enough to enter the prohibited region. In general, the greater the voltage spike or transient, the shorter the duration it can occur before equipment is damaged. ITI (CBEMA) Curve 500

Percent of Nominal Voltage (RMS or Peak Equivalent)

400

300 Prohibited Region Voltage Tolerance Envelope Applicable to Single-Phase 120-Volt Equipment 200

140 120 100 80 70

110 No Interruption in Function Region

90

No Damage Region

40 0 .001 c 1 s

.01 c

1c 10 c 1 ms 3 ms 20 ms

100 c 0.5 s

10 s

Steady State

Duration in Cycles (c) and Seconds (s)

ITI (CBEMA) Curve used with permission of Information Technology Industry Council.

10

In spite of the utility company’s effort to minimize voltage fluctuations and the manufacturer’s efforts to protect equipment, home electronic equipment is still susceptible to damage anytime supply voltage exceeds the manufacturer’s recommended tolerance. Sensitive electronic equipment is most vulnerable during overvoltage disturbances that exceed the voltage tolerance envelope of the ITI (CBEMA) curve, such as those caused by lightning or switching of loads on the distribution system.

0.01 Cycle

0.01 Cycle

Sensitive Equipment in the Home

600%

600%

400%

400%

200%

200%

100%

100%

By now you may be wondering what all of this has to do with the average home owner. In the past it was considered sufficient just to keep the lights on. The typical home had relatively few items at risk. Today’s modern homes, however, are full of complex and sensitive electronic equipment. Family rooms have everything from a simple television to complex home entertainment systems with DVD players and surround sound. Home offices include computers, fax machines, printers, and telephone systems. Traditional kitchen and laundry appliances have been replaced with refrigerators, stoves, microwave ovens, and dishwashers that use electronic components. It takes as little as one surge to damage these sensitive electronic components.

11

Review 1

12

1.

The most common supply system used in residential applications is a ____________ -phase, ____________ -wire system.

2.

In a residential system there is 240 volts between the two hot wires. From either hot wire to neutral there is ____________ volts.

3.

Residential electrical service can come from an overhead utility transformer or from a ____________ service run underground.

4.

According to ITI (CBEMA), the ____________ the voltage spike or curve, the shorter its duration can be before damage occurs.

5.

Voltage spikes that exceed either amplitude or duration of the voltage tolerance envelope will enter the ____________ region of the ITI (CBEMA) curve.

Sources of Voltage Surges

Surges from Outside the Home

There are several causes of electrical surges that can originate outside the home. Surges can occur when large electrical loads are turned on and off, such as electrical machinery at a nearby factory or at the utility company itself. Lightning is the most damaging source of surges. Lightning is caused by the attraction of positive and negative charges in the atmosphere. This results in a buildup and discharge of electrical energy. Lightning can occur within a cloud, from cloud to cloud, or from cloud to earth. According to the National Oceanic and Atmospheric Administration (NOAA) there is an estimated 2000 thunderstorms at any given moment in the world, resulting in 100 lightning strikes every second. There are over 22 million lightning strikes in the United States in an average year. A typical lightning strike consists of 20,000 to 100,000 amps at 30 million volts.

2000 Thunderstorms Occuring in the World at any Given Moment 100 Lightning Strikes Every Second 8 Million Lightning Strikes Every Day Over 22 Million Lightning Strikes in the United States in an Average Year

13

Electrical Equipment Damage

Lightning does not have to strike a home, or near a home to cause electrical damage. A lightning strike on a power line several miles away still has the potential to cause extensive electrical damage in a home. Lightning strikes on high voltage lines are generally dissipated by utility transmission lines.

Thunderstorm Locations

Thunderstorms occur everywhere in the United States. The following map shows the approximate mean annual number of days with thunderstorms in the United States.

14

Surges from Within the Home

Lightning isn’t the only source of electrical surges. Many devices that are sensitive to electrical surges also produce electrical surges. Motor driven equipment, such as garage door openers, refrigeration, and air conditioners are not the only sources of electrical surges within the home. Television, computers, microwave ovens, and modern gas ranges and furnaces that use electronic ignition can also cause line disturbances and surges.

Air Conditioner

Microwave Oven

Computer

Garage Door Opener Gas Stove with Electronic Ignition

Refrigerator

15

Surge Protection

There are a number of devices available to protect sensitive electronic equipment from surges. An understanding of terms associated with surge protectors will help provide an understanding of how they work. Units of Measurement

The International System of Units, known as SI (Système Internationale d’Unités), is used throughout the world. The SI system is more recently used in the United States.

Joule Rating

Surge protectors are commonly rated in joules (J), which is an SI unit of measurement for work done or energy expended. This rating provides an indication of how much energy a surge protector can absorb. The higher the joule rating, the more energy a surge protector can absorb. Work is accomplished when a force causes motion. In an electrical circuit, voltage applied to a conductor will cause electrons to flow. Voltage is the force and electron flow is the motion. The result of this work is power which is used by an electrical light or appliance connected to the circuit. Power is the rate work is done or the rate of energy usage. Power consumed is measured in watts (W). The watt is defined as the rate work is done in a circuit when one amp flows with one volt applied. If 120 volts were applied to a circuit that caused 0.625 amps of current to flow, the power consumed would be 75 watts. P = ExI P = 120 x 0.625 P = 75 watts

16

Another way to view this is to look at joules of energy used. One joule is equivalent to one watt of power for one second. In this example 75 joules of power is consumed every second. If a lamp were left on for an hour, 270,000 joules of energy would be used (3600 seconds x 75 watts).

Voltage

120 Volts

0.625 Amps

75 Watts 75 Joules per Second

Clamping Voltage

Clamping voltage is a measure of the voltage-limiting capability of a surge protector. Voltage at a lower level than the clamping voltage is passed on to the load. Voltage in excess of the clamping level is blocked.

Peak or Impulse Current Rating

Peak current rating specifies the maximum energy that can be dissipated from a single surge without causing the protecting device to be damaged. The higher the peak current rating the better the protection.

MOV

A metal oxide varistor (MOV) is a device commonly used in surge protectors. There are two characteristics of MOVs that make them desirable for surge protection. First, the resistance of an MOV decreases with an increase in voltage. In addition, MOVs are fast acting and can respond to a surge in just a few nanoseconds. This results in suppressing a surge before it has a chance to damage electronic equipment.

MOV

Circuit Symbol

17

How Surge Protectors Work

Under normal conditions an MOV provides a very high resistance path. Resistance can be several hundred thousand ohms, limiting the current flowing through the MOV and allowing most of the current to flow through the load. In residential applications the load can be a computer, television, or other commonly used electronic device. Fuse

Inductor

120 VAC Power Supply

MOV

Load

Normal Voltage

The voltage rating of an MOV is greater than the normal supply voltage. Therefore, when a surge occurs and the clamping voltage rating of the MOV is exceeded, the MOV switches from a high resistance path to a low resistance path. Surge voltage passes through the MOV to ground, bypassing the connected load. Better surge protectors have inductors in series with the load and MOV to the slow the rise in current. In addition, surge protectors may incorporate a fuse or miniature circuit breaker to protect circuits from longer overcurrent conditions. Fuse

Inductor

120 VAC Power Supply

MOV

Surge Voltage

18

Load

Example

It is important to note that a surge protector’s peak impulse rating applies to its ability to handle a surge. The lamp that used 270,000 joules in an hour would appear to far exceed the capability of a surge suppressor rated for 1500 joules. However, this is energy delivered to the load and not associated with current through the surge suppressor. Surges are typically short in duration, lasting only a few milliseconds. For example, a surge of 1000 volts at 100 amps would only provide 100 joules if the surge lasted one millisecond (1000 x 100 x 0.001).

Unsuppressed Surge

Warranty

Suppressed Surge

Although warranty is not a technical term, it is very important when considering a surge protection device. Better warranties provide both product and connected equipment replacement. The amount of replacement available varies with the product and the manufacturer.

19

Surge Arrester and TVSS

Surge arrester and transient voltage surge suppressor (TVSS) are two terms associated with surge protection devices that are often interchanged. Both devices protect equipment by providing a preferred path of surge current to ground. Surge arresters are discussed in the National Electrical Code® Article 280. Transient voltage surge suppressors are discussed in Article 285.

Surge Arrester Definition

NEC® Article 280.2 defines a surge arrester as a protective device for limiting surge voltages by discharging or bypassing surge current, and it also prevents continued flow of follow current while remaining capable of repeating these functions. The National Electrical Code® does not require the use of surge arresters, however; when surge arresters are used NEC®Article 280.21 permits them to be installed at the service entrance in front of the main disconnect. Article 280.3 requires a surge arrester to be connected to each ungrounded conductor. The following illustration shows two ways this requirement can be met. Power Source

A N B

Surge Arrester

Surge Arrester

A

A

B

N Service Entrance Load Center

G

B

N

G



20

TVSS Definition

NEC® Article 285.2 defines transient voltage surge suppressors as a protective device for limiting transient voltages by diverting or limiting surge current; it also prevents continued flow of follow current while remaining capable of repeating these functions. Transient voltage surge suppressors provides a similar protection function as a surge arrester. Transient voltage surge suppressors are generally installed to protect sensitive electronic equipment such as computers, telecommunications, and other electronic equipment. Two articles in the National Electrical Code® help provide distinction between a surge arrester and a transient voltage surge suppressor. Article 285.5 requires that TVSS devices be listed. This simply means that equipment meets appropriate standards and has been tested and found suitable for a specific purpose. There are a number of companies that test and list electrical products. One such company is Underwriters Laboratories (UL), which is a private company that is nationally recognized as an independent testing laboratory. Transient voltage surge suppressors must meet criteria for UL 1449. NEC® Article 285.21 specifies that when a TVSS device is used it must be installed on the load side of the service disconnect overcurrent protection. Power Source

A N B

A

B

TVSS N

G


21

Comparison

Although the NEC® definitions of a surge arrester and a transient voltage surge suppressor are similar, there are two things that distinguish the two. First, only surge arresters may be connected ahead of the disconnect (Article 230.82(3)). The National Electrical Code® requires that TVSS devices be located on the load side of the service disconnect overcurrent protection. The second difference is in the standards they are expected to meet. Products that pass UL safety tests can carry a UL label. UL has several categories of labels based upon the product tested. We have already learned that TVSS devices must meet the criteria for UL 1449. Surge arresters are also tested and must meet criteria for UL OXHD. Power Source

A N B Surge Arrester May be Installed in Front of the Main Disconnect (NEC® Article 280.82(3)) Meets Criteria for UL OXHD

Surge Arrester

A

B

TVSS Installed on Load Side of Service Disconnect Overcurrent Protection Only (NEC® Article 285.21) Meets Criteria for UL 1449 Note: UL 1449 standards are different for point-of-entry and point-of-use TVSS devices.

TVSS N

G



22

Review 2 1.

____________ is the most damaging source of surges.

2.

A typical lightning strike consists of ____________ to ____________ amps.

3.

Surge protectors are rated in ____________ , which is an indication of how much energy a surge protector can absorb.

4.

An ____________ is a device commonly used in surge protectors that exhibit a change of resistance with a change in voltage.

5.

Surge protectors typically provide a desired path to ____________ when a surge occurs, bypassing the connected load.

6.

A main difference between a surge arrester and transient voltage surge suppressor is that a transient voltage surge suppressor is connect to the ___________ side of the service disconnect overcurrent protection.

23

Point-of-Entry Surge Protection

Surge protection devices installed at the service entrance can divert surges to ground before they enter the premises. A properly installed and operating point-of-entry surge protector shields motor-driven appliances, such as refrigerators, dishwashers, electric washers and dryers, heaters, and air conditioners from damage.

24

Point-of-Entry Solutions

An electrical surge, whether it is caused by electrical equipment or lightning, always seeks ground. Any component between the source of the surge and ground can be damaged. Siemens circuit breaker surge arresters provide a preferred route to ground, bypassing expensive and sensitive equipment. Siemens offers product solutions for both Siemens load centers and load centers of other manufactures.

Type QP and TVSS Circuit Breaker Siemens Load Centers

Siemens Circuit Breaker Surge Suppressor

Primax Point-of-Entry Protector Siemens and All Other Load Centers

The Siemens circuit breaker and transient voltage surge suppressor (TVSS) module is comprised of a highly effective surge suppressor integrated with two 1-pole circuit breakers. Type QP Circuit Breaker

MOV

Indicator Lights

Surge Protection Circuitry

25

Visual Indication

Even the best point-of-entry surge protectors are subject to failure in the event of a catastrophic surge. Good surge protectors will sacrifice themselves and not the connected equipment. Better surge protection devices provide visual indication that the surge protection circuitry is functional and protecting the connected equipment. If the indicator lights are not illuminated the home owner should replace the surge protector promptly.

Installation

Installation is as simple as mounting a conventional circuit breaker in a Siemens load center. After power is switched off and the trim removed, the circuit breaker/surge arrestor plugs into place. A wire is provided to connect the ground side of the module to the load center’s neutral bus. It is best to position the circuit breaker/surge arrestor in the first position of the load center and connect the wire in the first neutral position. One device provides protection for the entire electrical system. The device does not require a dedicated space as it replaces two existing circuit breakers. Although the circuit breaker portion can be connected to any 120 volt circuits, connecting it to a lighting circuit provides additional visual indication that the device is working. If the device trips due to a high voltage surge, it is reset like any other circuit breaker in the panel.

26

Ratings

Clamping Rating Energy Rating Impulse Rating Warranty

Primax® Point-of-Entry Protector

The Primax point-of-entry protector is another option to shield motor-driven appliances against electrical power surge damage. Primax is mounted external to the load center so it can be used with Siemens or non-Siemens load centers. Two versions are available, side mount and back mount.

Back Mount

UL Listed

500 V at 3000 A 720 joules, line-to-line 40,000 A $20,000, includes kitchen and laundry room equipment connected to dedicated circuits

Side Mount

Primax is UL listed for installation before the main disconnect as a surge arrester (NEC® Article 280.21) or after the main disconnect as a transient voltage surge suppressor (NEC® Article 285.21). The following drawing illustrates a Primax pointof-entry surge protector connected as a TVSS. The Primax is connected to the load side of the main-service disconnect through a two-pole, 20 amp circuit breaker. Two LED lights indicate the protection status. In addition, if protection is disrupted there is an audible alarm.


27

Ratings

Clamping Rating Energy Rating Impulse Rating Warranty

400 V 1920 joules, line-to-line 60,000 A Major household appliances are covered against surge damage for 3 years and up to $10,000 when a Primax is installed by a qualified electrician. Primax surge protectors will be replaced if damaged during the first 5 years of ownership.

Review 3 1.

The Siemens circuit breaker and TVSS module is comprised of a point-of-entry surge suppression integrated with two 1-pole ___________ ___________.

2.

The ____________ point-of-entry surge protector can be used with Siemens or non-Siemens load centers.

3.

The Siemens circuit breaker and TVSS module is rated for ____________ joules.

4.

The Primax is UL listed for installation before the main disconnect as a ____________ ____________ or after the main disconnect as a TVSS.

5.

The Primax is rated for ____________ joules.

Note: See complete warranty for full information on Siemens point-of-entry surge protectors

28

Point-of-Use Surge Protection

Point-of-use surge protection consists of a power strip with surge protection circuitry incorporated. Point-of-use surge protection should be used anywhere expensive and sensitive electrical equipment is used. MOV On/Off Power Switch Indicator Light

Miniature Circuit Breaker Surge Protection Circuitry

Electrical Outlet

Home Entertainment

The use of expensive and sensitive electronic equipment in the home is on the rise. Today’s home entertainment centers, for example, include television sets, stereo equipment, DVD players, VCRs, and satellite or cable equipment.

Point of Use Surge Protector

29

Home Office

Today, millions of homes have home offices. Home offices include computers, fax machines, printers, copiers, scanners, and telephones. Home offices will benefit significantly from point-of-use surge protection, since the replacement cost of equipment is high. Home offices are frequently associated with a home business. The expense of lost business while equipment is down can be significant.


Basic Power Strips

30

Too often, home owners seek inexpensive solutions to connecting and protecting expensive equipment. Inexpensive extension cords, add-on outlets, and basic power strips provide no surge protection, leaving equipment susceptible to performance degradation and damage.

Basic Surge Protection

Home owners may also settle for an inexpensive surge protected power strip. Some of these may have a fuse or miniature circuit breaker that can be reset, but provide no visual indication that the surge protection circuitry is functioning. A home owner may think the connected equipment is protected, when in reality it is not.

Visual Indication

Good point-of-use surge protectors, like good point-of-entry surge protectors, will sacrifice themselves and not the connected equipment in the event of a catastrophic surge. It is important to note that in many point-of-use surge protectors, the electrical outlets continue to supply power to equipment even though the surge protection circuitry may have been damaged. Better point-of-use surge protection devices provide visual indication that the surge protection circuitry is functional and protecting the connected equipment.

31

Other Features

In addition, better point-of-use surge protectors are designed around the equipment they are intended to protect. Equipment is just as susceptible to damage from electrical surges on telephone and cable feeds as from the electrical power supply. Point-of-use surge protectors designed for use with home entertainment equipment should include surge protection circuitry for cable or satellite connections. Surge protection intended for use in the home office should include connections for a telephone, fax, and modem.

Visual Indication Ground OK

Cable, Satellite, Televison

Miniature Circuit Breaker Visual Indication Surge Protection Circuitry OK Telephone, Modem, Fax

TVSS

Point-of-use surge protectors are classified as transient voltage surge suppressors (TVSS) according to NEC® Article 285.21 requirements because they are installed on the load side of the service disconnect overcurrent protection. Point-of-use surge protectors should be UL 1449 listed. Power Source

A N B

A

N

B

G


32

POWERMAX®8

Siemens offers a wide range of point-of-use surge protectors. POWERMAX8 protectors have a single pulse energy rating of 1020 joules. POWERMAX8 surge protectors have a $100,000 lifetime warranty. Equipment damaged by electrical surge while properly connected to POWERMAX8 products will be repaired or replaced at fair market value. POWERMAX8 surge protectors are available in models specially designed for the home office, home entertainment centers, and satellite systems.

Catalog #: SPOWERMAX8 Multi-Use

Catalog #: SPOWERMAX8_T Home/Office In/Out Telecommunications

Catalog #: SPOWERMAX8_C Audio/Visual In/Out Coax

Catalog #: SPOWERMAX8_D Satellite System 1 In/Out Satellite 2 In/Out Coax 1 In/Out Telecommunications

33

MAX®6

MAX6 surge protectors have a single pulse energy rating of 672 joules and offer a $1,000,000 warranty. MAX6 products have add on modules for telephone or cable TV (ANT/CATV) connections.

MAX ANT/CATV Module

MAX TEL/1Module

MAX6

Note: See complete warranty for full information on Siemens point-of-use surge protectors

34

Whole-House Protection

Surge Protection Plan


No single product can protect equipment in a residence from all electrical surges. In this section we will learn how a tiered protection plan, consisting of point-of-use and point-of-entry surge protectors, help guard against disturbances from inside and outside the home.

Point-of-Entry Surge Protection

35

Point-of Entry Protection is not Enough

We have already learned that point-of-entry protectors can prevent electrical surges on the utility service from entering the home. Electrical surges can come from a lightning strike on or near high-voltage transmission lines or switching of primary circuits by local utilities.

A B

N TVSS


Surges from Within the Home

However, point-of-entry surge protectors are not whole-house protectors. Point-of-entry surge protectors cannot eliminate all electrical surges developed within the home. For example, an air conditioner can cause a small electrical surge every time it cycles on and off. Surges caused by equipment within the home are usually weaker than surges caused by lightning, however, they occur more frequently. These surges are distributed throughout the home’s electrical system, possibly causing problems with other connected equipment.

A N

B

TVSS


36

Exterior Wiring

Additionally, many homes have some form of exterior electrical wiring. Security gates, outdoor lighting, electronic dog fences, and swimming pool filtration equipment are just a few examples of outdoor appliances in use today.

Security Gate Control

Underground Wiring

Pool Filtration Lighting

Electronic Dog Fence

A cloud-to-earth lightning strike in close proximity to underground wiring can cause a voltage surge which has a direct path to the home distribution system.

A N

B

TVSS


37

Surges from Other Services

Most damage occurs from electrical surges that enter the home from outside services. We have already learned how lightning strikes can enter the home through the electrical utility. It is equally important to note that telecommunication and cable services can also conduct electrical surges into the home causing damage to televisions, modems, and telephones. The National Electrical Code® requires services to be grounded and bonded together. The purpose is to reduce fire and shock hazard in the event electric utility power conductors come in contact with communication conductors. However, this will not protect sensitive electrical and electronic equipment located within the house. Electrical Service

Telecommunication

Cable TV

Services Grounded and Bonded Together


38

Adding Point-of-Use

The addition of appropriate point-of-use surge protectors adds protection to equipment such as computers, home entertainment systems, and telecommunications equipment. These systems would otherwise be vulnerable to surges caused by: •

surges caused by lightning entering the home through unprotected underground wiring.

•

surges from cable or telecommunication systems.

•

switching, such as an air conditioner or other home electrical equipment.

A N

B

TVSS


Point-of-Use Protection is not Enough

Homeowners often mistakenly think that point-of-use surge protection is sufficient and forgo the extra expense of point-ofentry surge protection. It is impractical to connect point-of-use surge protectors at every outlet to protect appliances such as washing machines, dryers, dishwashers, stoves, ovens, garage door openers, air conditioners, and heaters. Some appliances are hard wired and may require a qualified electrician to install a surge protector.

39

Surge Current

Point-of-entry surge protectors are generally more robust and able to withstand higher values of surge current. A nearby lightning strike, for example, can result in surge current as high as 10,000 amps at the point-of-entry. Siemens QP and TVSS circuit breaker, installed in a Siemens load center can withstand a current impulse as high as 40,000 amps. Siemens Primax® point-of-entry protector can withstand a current impulse as high as 60,000 amps. Although some point-of-use surge protectors are also capable of handling larger surge currents, it is much better to shunt this high current to ground before it enters the distribution system. In addition, many appliances may not be connected to a pointof-use surge protector.

Clamping Voltage

Another advantage to using a tiered system is the ability of point-of-entry surge protectors to reduce surge voltage at the service entrance. Primax point-of-entry surge protectors, for example, have a clamping voltage of 400 volts. An initial 2500 volt surge from a lightning strike would be clamped to 400 volts at the point of entry. Reducing voltage and corresponding surge current makes it easier for point-of-use surge protectors, which have a UL 1449 maximum clamping voltage of 330 volts, to handle the overvoltage. In addition, an extra layer of protection to sensitive and expensive electronic equipment is provided.

2500 Volt Surge

400 Volt Surge 330 Volt or Less Surge Point-of-Entry

40

Point-of-Use

Surge Protection Kits

Siemens offers surge protection kits designed to provide the necessary tiered protection. The basic kit consists of the Type QP and TVSS circuit breaker and two POWERMAX8 surge protectors. The deluxe kit consists of the Primax point-of-entry protector and MAX6 surge protectors with ANT/CATV and TEL modules. Basic Kit

Deluxe Kit

Type QP and TVSS Circuit Breaker

Primax Point-of-Entry Protector

POWERMAX8 TEL

MAX6 with ANT/CATV Module

POWERMAX8 COAX

MAX6 with TEL/1Module

41

Review 4 1.

____________ -of- ____________ surge protection is typically used with home entertainment centers and home offices.

2.

Point-of-use protectors are classified as ____________ ____________ surge suppressors.

3.

____________ is a POWERMAX8 surge protector typically used in the home office.

4

Surges can also enter the home distribution system from ____________ . a. b. c. d.

5.

42

outdoor wiring telephone service cable all of the above

Point-of-use surge protectors should be ____________ listed.

Review Answers

Review 1

1) single-phase, three-wire; 2) 120; 3) lateral; 4) greater; 5) Prohibited.

Review 2

1) Lightning; 2) 20,000 to 100,000; 3) joules; 4) MOV; 5) ground; 6) load.

Review 3

1) circuit breakers; 2) Primax; 3) 720; 4) surge arrester; 5) 1920.

Review 4

1) Point-of-use; 2) transient voltage; 3) SPOWERMAX8_T; 4) d; 5) UL 1449.

43

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. After completing the test, mail the answer sheet in for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. 1.

Sensitive electrical equipment manufactured to ITI (CBEMA) guidelines should be able to sustain a 200% overvoltage surge for ____________ without sustaining damage. a. b. c. d.

2.

The most damaging source of electrical surges comes from ____________ . a. b. c. d.

3.

.02 10 200 100,000

____________ is a measure of the voltage-limiting capability of a surge protector. a. b. c. d.

44

motor driven equipment lightning strikes cable and telecommunication services utility companies switching primary circuits

An electrical surge of 1000 volts at 100 amps with a duration of .002 seconds supplies ____________ joules of energy to the connected equipment. a. b. c. d.

4.

1 ms 3 ms 20 ms 0.5 seconds

Peak current rating Clamping voltage Peak impulse Joule rating

5.

A/An ____________ is a device used in surge protectors that switches from a high resistance to a low resistance when a voltage surge occurs. a. b. c. d.

6.

MOV inductor miniature circuit breaker TVSS

NEC® Article 285.21 specifies that a transient voltage surge suppressor be connected ____________ . a. at the service entrance in front of the main disconnect b. on the load side of the service disconnect overcurrent protection c. at the point of use d. either in front of or on the load side of the service disconnect overcurrent protection

7.

According to NEC® Article 230.82(3), only ____________ may be connected ahead of the service entrance main disconnect. a. b. c. d.

8.

TVSS devices point-of-use devices point-of-entry devices surge arresters

Point-of-use surge protectors meet NEC® Article 285.21 requirements for a TVSS device because they are ____________ . a. installed on the load side of the service disconnect overcurrent protection b. portable c. installed ahead of the service entrance main disconnect d. installed ahead of the equipment to be protected

9.

Surge protectors are rated in ____________ , which is an indication of how much energy a surge protector can handle. a. b. c. d.

watts volts joules amps

45

10. ____________ tradename(s) for Siemens point-of-use surge protectors. a. b. c. d. 11.

MAX®8 is a POWERMAX®6 is a MAX®8 and POWERMAX®6 are MAX®6 and POWERMAX®8 are

____________ is a good choice for use in a home/office. a. b. c. d.

SPOWERMAX8_T SPOWERMAX8_C SPOWERMAX8_D MAX6 with ANT/CATV module

12. The clamping voltage rating of a Type QP and TVSS surge protector is ____________ volts. a. b. c. d.

130 250 330 500

13. The impulse rating of a Type QP and TVSS surge protector is ____________ amps. a. b. c. d.

3000 10,000 40,000 60,000

14. The clamping voltage rating of a Primax point-of-entry protector is ____________ volts. a. b. c. d.

250 330 400 500

15. The impulse rating of a Primax point-of-entry protector is ____________ amps. a. b. c. d.

46

3000 10,000 40,000 60,000

16. Point-of-entry surge suppressors should meet criteria for ____________ . a. b. c. d. 17.

UL 1449 NEC® Article 280 NEC® Article 285 UL 1449 and NEC® Article 280

Electrical surges from lightning strikes can also enter the home distribution system from ____________ . a. b. c. d.

outdoor wiring telephone service cable all of the above

18. Point-of-use surge suppressors should meet criteria for ____________ . a. b. c. d.

ITI (CBEMA) NEC® Article 280 UL 1449 UL OXHD

19. The Siemens Type QP and TVSS surge suppressor is comprised of point-of-entry surge suppression integrated with ____________ a. b. c. d.

a single-pole circuit breaker two single-pole circuit breakers a two-pole circuit breaker two two-pole circuit breakers

20. A tiered protection plan, consisting of ____________ is recommended to protect from electrical disturbances from inside and outside the home. a. b. c. d.

point-of-entry and point-of-use surge protectors point-of-use and TVSS surge protectors point-of-entry surge arrester and point-of-entry TVSS point-of-use surge protectors

47



48

Table of Contents

Introduction ..............................................................................2 Distribution Systems ................................................................4 Switchboard Definition ........................................................... 10 Overcurrent Protective Devices .............................................. 15 Switchboard Construction ......................................................20 Service Section.......................................................................28 Service Section Main Disconnect Devices .............................32 Distribution Section ................................................................36 Power Supply Systems ...........................................................39 Service Entrance Equipment ..................................................42 Switchboard Grounding ..........................................................45 Ground Fault Protection ..........................................................50 Switchboard Ratings...............................................................54 SB1, SB2, and SB3 Switchboards ...........................................57 RCIII Switchboards .................................................................61 Super Blue Pennant Switchboards .........................................64 Commercial Metering Switchboards ......................................66 Speciality Service Entrance Switchboards..............................68 Information Needed To Order Switchboards ...........................72 Review Answers..................................................................... 74 Final Exam ..............................................................................75

1

Introduction

Welcome to another course in the STEP 2000 series, Siemens Technical Education Program, designed to prepare our distributors to sell Siemens Energy & Automation products more effectively. This course covers Switchboards and related products. Upon completion of Switchboards you should be able to:

2

•

Explain the role of switchboards in a distribution system

•

Define a switchboard according to the National Electrical Code

•


•

Identify various components of a switchboard

•

Identify various service entrance methods

•

Explain the difference between hot and cold sequence in relation to current transformers

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Identify types of main and distribution devices available for Siemens switchboards

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Identify various Siemens switchboards

This knowledge will help you better understand customer applications. In addition, you will be better able to describe products to customers and determine important differences between products. You should complete Basics of Electricity and Molded Case Circuit Breakers before attempting Switchboards. An understanding of many of the concepts covered in these courses is required for Switchboards. If you are an employee of a Siemens Energy & Automation authorized distributor, fill out the final exam tear-out card and mail in the card. We will mail you a certificate of completion if you score a passing grade. Good luck with your efforts. Clampmatic, Vacu Break, Sensitrip, and Speedfax are registered trademarks of Siemens Energy & Automation, Inc. ACCESS, Sentron, and Super Blue Pennant are trademarks of Siemens Energy & Automation, Inc. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA 02269. Portions of the National Electrical Code are reprinted with permission from NFPA 70-2002, National Electrical Code Copyright, 2001, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and official position of the National Fire Protection Association on the referenced subject which is represented by the standard in its entirety. Underwriters Laboratories Inc. and UL are a registered trademarks of Underwriters Laboratories Inc., Northbrook, IL 60062. National Electrical Manufacturers Association is located at 2101 L. Street, N.W., Washington, D.C. 20037. The abbreviation “NEMA” is understood to mean National Electrical Manufacturers Association. Other trademarks are the property of their respective owners.

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Most of us are familiar with the distribution system found in the average home. Power, purchased from a utility company, enters the house through a metering device. The power is then distributed from a load center to various branch circuits for lighting, appliances, and electrical outlets.

Commercial and Industrial Distribution

Distribution systems used in commercial and industrial locations are more complex. An industrial distribution system consists of metering devices to measure power consumption, main and branch disconnects, protective devices, switching devices to start and stop power flow, conductors, and transformers. Power may be distributed through various switchgear and switchboards, transformers, and panelboards. Good distribution systems don’t just happen. Careful engineering is required so that the distribution system safely and efficiently supplies adequate electric service and protection to both present and possible future loads.

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Distribution of Current

Switchboards are used in a building’s electrical distribution system. A switchboard divides a large electrical current into smaller currents used to power electrical equipment. Switchboards can be found in applications ranging from small office buildings to large industrial complexes.

Small Office Building

A small office building, for example, might require 120 volts for interior lighting and receptacles, and 208 volts for heating, air conditioning, and exterior lighting. In this example the utility company supplies 208/120 volt, three-phase, four-wire service. The main incoming line is divided into four feeders. The two outer feeders supply power directly to the 208 volt heating and air conditioning units. The two inner feeders are divided into a number of branch circuits. One set of branch circuits supplies power to exterior lighting (208 volts). The second set of branch circuits supplies power to interior lighting and receptacles (120 volts).

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The utility company supplies power from a transformer with a wye connected secondary. The secondary winding of the transformer produces 208/120 VAC. This is referred to as threephase, four wire (3Ø4W). Single-phase 120 VAC is available between any phase wire and neutral. Single-phase 208 VAC is available between any two phases.

Incoming power is metered by the utility company. In this example power is supplied to the building through a main service disconnect. A switchboard divides the power into four feeders for distribution throughout the building.

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Medium Industrial Plant

Another example of a distribution system is a medium industrial plant. In this example the incoming power is 480/277 volts, three-phase, four-wire. Three feeders are used. The first feeder is used for various types of power equipment. The second feeder supplies a group of 480 VAC motors. The third feeder is used for 120 volt lighting and receptacles.

The utility company supplies power from a transformer. The secondary winding of the transformer produces 480/277 VAC.

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In this example power from the utility company is metered and enters the plant through a distribution switchboard. The switchboard serves as the main disconnecting means. The feeder on the left feeds a distribution switchboard, which in turn feeds a panelboard and a 480 volt, three-phase, three-wire motor. The middle feeder feeds another switchboard, which divides the power into three, three-phase, three-wire circuits. Each circuit feeds a busway run to 480 volt motors. The feeder on the right supplies 208/120 volt power, through a step-down transformer, to lighting and receptacle panelboards. Branch circuits from the lighting and receptacle panelboards supply power for lighting and outlets throughout the plant.

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Switchboard Definition

Definition

The National Electrical Code® (NEC®) defines a switchboard as a large single panel, frame, or assembly of panels on which are mounted, on the face or back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. Switchboards are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets (Article 100-definitions). The following drawing illustrates a switchboard made up of a group of two sections. Several overcurrent protective devices (molded case circuit breakers) are mounted on the switchboard.


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Buses are mounted inside the switchboard.

Depending on the design, switchboards may be installed next to a wall or away from the wall to permit accessibility to the rear of the switchboard.

Note: Switchboards are built according to standards set by Underwriters Laboratory (UL 891) and the National Electrical Manufacturers Association (NEMA PB2). Basic requirements for switchboards are also covered by the National Electrical Code® Article 408. You are encouraged to become familiar with this material. NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association.

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Instruments/Metering

The NEC® definition of a switchboard includes instrumentation. Siemens offers a full line of power meters for use in switchboards, which include the 9200, 9300, 9330, 9350, 9500, 9600, and 9700. These meters are compatible with the ACCESS™ power management and control system. ACCESS is a networked power-monitoring and control system that provides sophisticated power-management capabilities. The flexibility and modularity of the complete ACCESS system make it possible to customize a power-management solution for almost every situation. Siemens power meters replace multiple traditional analog meters and selector switches, and allow remote monitoring of power-related parameters. Among these are phase voltage and current, line voltage and current, neutral current, kW hours, kW demand, power factor, and line frequency. Data-logging and power-management calculations are easily accomplished using ACCESS and WinPM.


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WinPM

WinPM™ is supervisory software designed for monitoring and control of a facility’s electrical distribution system. WinPM can monitor an entire electrical system consisting of hundreds of field devices in multiple locations. Alarms can be setup to trigger if a specific value, such as voltage, current, or KW demand, is exceeded. Alarms can alert via audible and visual messages on a PC, fax, or pager message, and/or automatically control a connected device. Power quality, such as transients, sags, swells, and harmonics, can be monitored and analyzed by viewing triggered waveforms, continuous data sampling, relay trip logs, and setpoint event messages. Historical data logs can be generated to provide load profile information, kilowatt demand usage patterns, harmonic, and power factor trends. These historical data logs can provide trending on any measured value.

The STEP 2000 book, Power Monitoring and Management with ACCESS, provides more information on power meters and the ACCESS system.

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Review 1 1.

The phase-to-neutral voltage of a wye-connected transformer with a phase-to-phase voltage of 208 volts is ____________ volts.

2.

The phase-to-neutral voltage of a wye-connected transformer with a phase-to-phase voltage of 480 volts is ____________ volts.

3.

According to the National Electrical Code® definition, switchboards ___________ . a are accessible from the front only b are accessible from the rear only c may be accessible from the front and rear

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4.

Switchboards are built according to standards set by ____________ and ____________ .

5.

Basic requirements for switchboards are given in NEC® Article ____________ .

Overcurrent Protective Devices

Excessive current is referred to as overcurrent. The National Electrical Code® defines overcurrent as any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault (Article 100-definitions). Current flow in a conductor always generates heat. The greater the current flow, the hotter the conductor. Excess heat is damaging to electrical components. For that reason, conductors have a rated continuous current carrying capacity or ampacity. Overcurrent protection devices are used to protect conductors and electrical equipment from excessive current flow. These protective devices are designed to keep the flow of current in a circuit at a safe level to prevent the circuit conductors from overheating.


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Circuit protection would be unnecessary if overloads and short circuits could be eliminated. Unfortunately, overloads and short circuits do occur. To protect a circuit from these currents, a protective device must determine when a fault condition develops and automatically disconnect the electrical equipment from the voltage source. An overcurrent protection device must be able to recognize the difference between overcurrents and short circuits and respond in the proper way. Slight overcurrents can be allowed to continue for some period of time, but as the current magnitude increases, the protection device must open faster. Short circuits must be interrupted instantly. Fusible Disconnect Switch

A fusible disconnect switch is one type of device used in switchboards to provide overcurrent protection. Properly sized fuses located in the switch open the circuit when an overcurrent condition exists.

Fuse

A fuse is a one-shot device. The heat produced by overcurrent causes the current carrying element to melt open, disconnecting the load from the source voltage.

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Nontime-Delay Fuses

Nontime-delay fuses provide excellent short circuit protection. When an overcurrent occurs, heat builds up rapidly in the fuse. Nontime-delay fuses usually hold 500% of their rating for approximately one-fourth second, after which the currentcarrying element melts. This means that these fuses should not be used in motor circuits which often have inrush currents greater than 500%.

Time-Delay Fuses

Time-delay fuses provide overload and short circuit protection. Time-delay fuses usually allow five times the rated current for up to ten seconds to allow motors to start.

Fuse Classes

Fuses are grouped into classes based on their operating and construction characteristics. Each class has an ampere interrupting capacity (AIC) which is the amount of fault current they are capable of interrupting without destroying the fuse casing. Fuses are also rated according to the maximum continuous current and maximum voltage they can handle. Underwriters Laboratories (UL) establishes and standardizes basic performance and physical specifications to develop its safety test procedures. These standards have resulted in distinct classes of low voltage fuses rated at 600 volts or less. The following chart lists the fuse class and its AIC rating.

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Class R Fuseholder

An optional Class R fuseholder can be used. The Class R rejection clip contains a pin that permits only the notched Class R fuse to be inserted. This prevents a lower rated fuse from being used.

Circuit Breakers

Another device used for overcurrent protection is a circuit breaker. The National Electrical Code® defines a circuit breaker as a device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating. Circuit breakers provide a manual means of energizing and de-energizing a circuit. In addition, circuit breakers provide automatic overcurrent protection of a circuit. A circuit breaker allows a circuit to be reactivated quickly after a short circuit or overload is cleared.


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Ampere Rating

Like fuses, every circuit breaker has a specific ampere, voltage, and fault current interruption rating. The ampere rating is the maximum continuous current a circuit breaker can carry without exceeding its rating. As a general rule, the circuit breaker ampere rating should match the conductor ampere rating. For example, if the conductor is rated for 20 amps, the circuit breaker should be rated for 20 amps. Siemens breakers are rated on the basis of using 60° C or 75° C conductors. This means that even if a conductor with a higher temperature rating were used, the ampacity of the conductor must be figured on its 60° C or 75° C rating. There are some specific circumstances when the ampere rating is permitted to be greater than the current carrying capacity of the circuit. For example, motor and welder circuits can exceed conductor ampacity to allow for inrush currents and duty cycles within limits established by NEC®. Generally the ampere rating of a circuit breaker is selected at 125% of the continuous load current. This usually corresponds to the conductor ampacity which is also selected at 125% of continuous load current. For example, a 125 amp circuit breaker would be selected for a load of 100 amps.

Voltage Rating

The voltage rating of the circuit breaker must be at least equal to the circuit voltage. The voltage rating of a circuit breaker can be higher than the circuit voltage, but never lower. For example, a 480 VAC circuit breaker could be used on a 240 VAC circuit. A 240 VAC circuit breaker could not be used on a 480 VAC circuit. The voltage rating is a function of the circuit breaker’s ability to suppress the internal arc that occurs when the circuit breaker’s contacts open.


Circuit breakers are also rated according to the level of fault current they can interrupt. When applying a circuit breaker, one must be selected to sustain the largest potential short circuit current which can occur in the selected application. Siemens circuit breakers have interrupting ratings from 10,000 to 200,000 amps. To find the interrupting rating of a specific circuit breaker refer to the Speedfax catalog.

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Switchboard Construction

There are several components that make up a switchboard. Switchboards consist of a frame, overcurrent protective devices, buses, instrumentation, and outer covers. Frame

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The frame of the switchboard houses and supports the other components. The typical Siemens switchboard frame is 90 inches high and 38 inches wide. Optional height of 70 inches and widths of 32 inches and 46 inches are available.

Bus

A bus is a conductor that serves as a common connection for two or more circuits. It is represented schematically by a straight line with a number of connections made to it. NEC® article 408.3 states that bus bars shall be located so as to be free from physical damage and shall be held firmly in place.

NEMA Arrangement

Bus bars are required to have phases in sequence so that an installer can have the same fixed-phase arrangement in each termination point in any switchboard. This is established by NEMA (National Electrical Manufacturers Association). It is possible to have a non-NEMA phase sequence which would have to be marked on the switchboard. Unless otherwise marked, it is assumed that bus bars are arranged according to NEMA. The following diagram illustrates accepted NEMA phase arrangements.


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Buses are mounted within the frame. Horizontal buses are used to distribute power to each switchboard section. Vertical buses are used to distribute power via overcurrent devices to the load devices. Standard bus bars on Siemens switchboards are made of aluminum, but copper bus bars are available as an option.

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The following rear view drawing of a switchboard illustrates vertical and horizontal bus bar connection. (The vertical phase bus bars appear to be in reverse order because they are viewed from the rear. The bus bars are in the proper NEMA order as viewed from the front.) A bus connector makes a mechanical and electrical connection between a vertical bus bar and its corresponding horizontal bus bar. In this drawing the connector can be clearly seen on the neutral bus. Compression lugs provided on this switchboard accept properly sized incoming power cables.

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Splice Plates

Splice plates are used to join the horizontal bus bars of adjoining switchboard sections, as illustrated in the following rear view drawing. To make additional distribution sections easier to install when they are needed, the horizontal bus is extended and predrilled to accept splice plates. A new section is set flush against an existing section. The old and new sections are connected together with splice plates. The extended horizontal bus is also referred to as through-bus. The load requirements in downstream distribution sections is generally less than in upstream service sections. The capacity of the through-bus is tapered, or reduced downstream as load falls off. The through-bus is tapered to a minimum of one-third the ampacity of the incoming service mains. Full-capacity, or non-tapered, through-bus is available as an option. The ampacity of non-tapered through-bus remains constant throughout the switchboard.

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Protective Devices

Operator components are mounted on the front side of the switchboard. This includes protective devices, such as circuit breakers and disconnect switches, which can be covered by a trim panel. These devices are mounted to the bus bars using straps connected to the line side of the devices.

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Dead Front and Trim

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Cover panels are installed on the switchboard so that no live parts are exposed to the operator. This is referred to as dead front. The panels are also used as trim to provide a finished look to the switchboard. A product information label identifies the switchboard type, catalog number, and voltage and amperage rating.

Pictorial

Switchboards can be shown pictorially using block diagrams and/or one-line diagrams. The following pictorial illustrates a two section switchboard.

Review 2 1.

The rated continuous current carrying capacity of a conductor is known as ____________ .

2.

__________ - delay fuses provide overload and short circuit protection.

3.

The interrupting rating of a Class R fuse is ____________ amps.

4.

The height of the standard Siemens switchboard frame is ____________ inches.

5.

A ____________ is a conductor that serves as a common connection for two or more circuits.

6.

____________ plates join horizontal buses between two adjoining switchboard sections.

7.

The extended horizontal bus that connects one section to another is referred to as ____________ - ___________

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Service Section

Typical switchboards consist of a service section, also referred to as the main section, and one or more distribution sections. The service section can be fed directly from the utility transformer. In addition to the main disconnect, the service section usually contains utility or customer metering provisions.

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Service Entrance Methods

Several options are available to bring power into the switchboard service section. Cable can be brought into the switchboard from the top or the bottom. Cable can be brought into the top of the switchboard through conduit. If the cable is a large diameter and more room is needed a pull box, available in 10” to 30” heights, can be added. A bus duct entrance can be used when metal bus is used instead of cables.

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Cable may enter through a conduit to a disconnect that is fed from the bottom. A pull section can be added to the side of the service section to pass cable to the top of the switchboard. Depending on the cable bending space, cable can be connected directly to the lugs or to a cross bus. A cross bus brings the bus connections to the pull section eliminating the need to bend cables.

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Hot Sequence

Metering can either be hot sequence or cold sequence. This refers to whether or not power is still applied to the utility meter when the main disconnect is switched off. The following drawing illustrates hot sequence. When the main disconnect is open, power is removed from the load. Power is still applied to the utility meter.

Cold Sequence

The following drawing illustrates cold sequence. When the main disconnect is open, power is removed from the load and the utility meter.

Hot sequence metering on the line side of the main disconnect is normal, but cold sequence metering on the load side of the main disconnect can also be provided.

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Service Section Main Disconnect Devices

The service section of Siemens switchboards will accommodate a variety of main protective devices. Selection depends on the characteristics of the electrical system and the needs of the customer. Fusible Switches

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One type of protective device is the Siemens Vacu-Break® fusible switch. Fusible switches are available in ampere ratings up to 1200 amps at 600 VAC.

HCP Fusible Switch

The HCP type fusible switch is another device that can be used in the service section as a disconnect device. Visible contacts provide a visual indication concerning the state of the switch before servicing. HCP fusible switches are available with ampere ratings from 400 to 1200 amps. HCP fusible switches are suitable for use on systems with up to 200,000 amps of available fault current with used with Class J or Class L fuses.

MCCBs

The Sentron™ Series molded case circuit breakers (MCCB) can also be used as main service section protective devices. Sentron Series circuit breakers are available with ampere ratings from 400 to 2000 amps, and interrupting ratings from 10,000 to 200,000 amps. The Sentron Series circuit breaker is also available with solid state protection, referred to as Sensitrip® III. Sensitrip III breakers are available with ampere ratings from 400 to 3200 amps, and interrupting ratings up to 200,000 amps.

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Handle Extension

It can be difficult to operate some of the handles on the larger circuit breakers. A handle extension is available which allows more leverage to be applied to the circuit breaker handle. This makes opening and closing the circuit breaker easier.

ICCBs

Insulated case circuit breakers (ICCB) can be applied in applications from 100 to 5000 amps through 600 VAC. There are four ICCB frames: 1200, 2000, 3200, and 5000 amps. Interchangeable rating plugs and a continuous current adjustment are provided with each trip unit. The frame ampere rating is determined by the current sensors in the breaker. Interrupting ratings are available in ratings up to 200,000 amps. ICCBs can be fixed mounted or drawout mounted.

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Bolted Pressure Switch

Bolted pressure switches can also be used as a main disconnect. Bolted pressure switches are available in 800, 1200, 1600, 2000, 2500, 3000, and 4000 amp frames. The maximum short circuit current withstandability is 200,000 amps. Bolted pressure switches are rated for 240 VAC, 480 VAC, and 600 VAC.

RL Power Circuit Breakers

RL power circuit breakers can also be used in switchboards. These circuit breakers are available in 800 to 5000 amp frames at 600 VAC. RL power circuit breakers are drawout mount.

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Distribution Section

The distribution section receives power from the service section and distributes it to various downstream loads.

Rear Alignment

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Depending on the design of a specific switchboard, the service section cabinet may be deeper than the distribution section. This is due to the size of the main disconnect device and associated bus requirements. The rear of all sections align so the switchboard may be installed against a wall. This is referred to as rear alignment.

Front and Rear Aligned

Switchboards can also be front and rear aligned, if the depth of the service section and distribution section are the same. In some switchboards the circuit protection devices and bus may require a deeper cabinet. In other switchboards extra depth may be added as an option.

Protective Devices

Like the service section, the distribution section will accommodate a variety of protective devices. Selection depends on the characteristics of the electrical system. In addition, motor control starters can also be used in switchboards. Device

Current Rating

Vacu-Break® Fusible Switches Bolted Pressure Switches HCP Switches Molded Case Circuit Breakers Insulated Case Circuit Breakers LV Power Circuit Breakers

30-1200 amps 800-4000 amps 400-1200 amps 15-3200 amps 100-5000 amps 800-4000 amps

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Review 3 1.

Typical switchboards consist of a ____________ section and usually one or more ____________ section.

2.

A ____________ ____________ , available in 10” to 30” heights, can be added to the top of a switchboard to allow room for large diameter cable.

3.

A ____________ ____________ is added to accommodate cable entering the bottom of a switchboard and connected to the bus at the top of a switchboard.

4.

____________ ____________ means that power is still applied to the utility meter when the main disconnect is open.

5.

____________ ____________ means that power is removed from the utility meter when the main disconnect is open.

6.

Which of the following is suitable for use as a main disconnect in the service section? a. b. c. d. e. f.

7.

fusible switch molded case circuit breaker insulated case circuit breaker bolted pressure switch RL power circuit breaker all the above

The ____________ section receives power from the service section and distributes it to various downstream loads.

8. ____________ ____________ refers to a switchboard where the service section may be deeper than the distribution section, and the rear of all sections are aligned.

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Power Supply Systems

Switchboards receive power from a variety of sources. Downstream switchboards may receive power from upstream switchboards or disconnect switches, however, power for the distribution system originates from a utility power company. Voltage from the power company is stepped down through transformers for distribution systems. The following are some examples of systems in use. The amount of voltage on the secondary depends on how much voltage is on the primary and the ratio between the primary and secondary. The following examples are representative of some voltages commonly found in distribution systems. 1Ø3W

The following diagram illustrates one of the most common single-phase, three-wire (1Ø3W) distribution systems in use today. There are 240 volts across the full secondary of the transformer and 120 volts between the neutral and either end of the transformer. The neutral is the third wire.

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3Ø4W, Wye-Connected

The following illustration shows the secondary of a 480 Y/277 V three-phase, four-wire (3Ø4W), wye-connected transformer. The “480 Y” indicates the transformer is wye-connected and has 480 volts between any two phases. The “277 V” indicates there are 277 volts between any phase and neutral (N). Phaseto-phase voltage is 1.732 times phase-to-neutral voltage (277 x 1.732 = 480). Neutral is the fourth wire.

3Ø3W, Delta-Connected

Another method used in connecting transformers is a delta secondary. In this example 480 volts is available phase-tophase.

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3Ø4W, Delta-Connected

A three-phase, four-wire, delta-connected secondary works a little differently. The following illustration shows a deltaconnected secondary with 240 volts phase-to-phase. The midpoint of one phase winding is grounded to provide 120 volts between phase A and neutral and 120 volts between phase C and neutral. Between phase B and neutral, however, the voltage is 208 volts. This is referred to as the high leg. The high leg can be calculated by multiplying the phase A to neutral voltage times 1.732 (120 x 1.732 = 208). Single-pole breakers should not be connected to the high leg. NEC® Article 215-8 requires that the high leg bus bar or conductor be permanently marked with a finish that is orange in color. This will help prevent electricians from connecting 120 volt singlephase loads to the 208 volt high leg. Four-wire, delta-connected transformers should always be wired so that the B phase to neutral is the high leg.

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Service Entrance Equipment

Switchboards are often used as service entrance equipment for a building. The service section of a switchboard refers to the section of a switchboard which receives incoming power. This power can be fed directly from utility power. Power can also be fed to the section from another source, such as switchboard or disconnect switch somewhere upstream. Service entrance equipment refers to the equipment through which the power supply enters the building. The switchboard in the following drawing is considered service entrance equipment because it is where power enters the building. The incoming power supply is connected to this equipment which provides a means to control and cut off the supply. The National Electrical Code® discusses service entrance equipment in Article 230. Switchboards used as service entrance equipment must be approved and labeled as such. All Siemens Sentron™ Series switchboards are factory labeled as suitable for service entrance equipment when specified for service entrance.


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Six Disconnect Rule

Service entrance conductors must have a readily accessible means of being disconnected from the power supply. NEC® Article 230.71 specifies that for each set of service entrance conductors no more than six switches or circuit breakers shall be used to disconnect and isolate the service from all other equipment. In the following example, a single main circuit breaker will disconnect power to all equipment being supplied by the service. There can be as many feeder and branch disconnect devices as needed.

In another example, a switchboard may be equipped with up to six circuit breakers to disconnect power to all equipment being supplied by the service. In any case, the circuit breaker must be clearly labeled for the load it supplies.


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It is important to note that the “six disconnect rule” refers to the number of disconnects and not the number of poles. For example, in the illustration shown below there are 18 poles but only six circuit breakers. Three poles are mechanically linked together to form one disconnect device. In the illustrated configuration the service can be disconnected with no more than six operations of the hand. This arrangement meets the “six disconnect rule” .

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Switchboard Grounding

Grounding is an important aspect of any electrical system and must be considered carefully. Article 250 of the National Electrical Code® defines ground as a conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth. The following illustration, for example, shows the neutral (N) conductor of a wye-connected transformer connected to ground.

There are two objectives to the intentional grounding of electrical equipment:

•

Keep potential voltage differentials between different parts of a system at a minimum which reduces shock hazard.

•

Keep impedance of the ground path to a minimum. The lower the impedance the greater the current is in the event of a fault. The greater the current the faster an overcurrent device will open.


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Neutral Disconnect Link

If a switchboard service section is intended to be used as service entrance equipment, provision must be included to isolate the neutral bus from the grounded neutral bus. A neutral disconnect link is provided for this purpose. The following drawing shows the disconnect link in place.

This removable link allows the branch neutral to be checked for continuity on the load side of the main disconnect. The following drawing shows the disconnect link removed.

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Service Entrance Grounding In the following drawing a switchboard is used as service entrance equipment. Power to the service section is received from a 3Ø4W service. The neutral is always grounded in service entrance equipment. The neutral is connected to ground through a neutral to ground connection and ground bus bar. The ground bus bar is connected to the frame of the switchboard, which is connected to the system or earth ground. The neutral disconnect link is left in place to supply downstream loads. Three-phase, four-wire power is then supplied to downstream loads.

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Downstream Equipment

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The neutral is only connected to ground at the service entrance. When downstream equipment is used the neutral is isolated in that equipment. As shown in the following illustration, the neutral is connected to earth ground through the ground bus bar of the service entrance switchboard. In this example a second switchboard is used downstream of the service entrance switchboard. The enclosure of the downstream switchboard is connected to ground through a grounding conductor back to the service equipment. The neutral is not connected to ground in the downstream switchboard. Notice also that the second (downstream) switchboard does not have a neutral disconnect link. Neutral disconnect links are not required in switchboards used as non-service entrance equipment. Similarly the second switchboard will feed additional downstream loads.

Review 4 1.

If the secondary of a four-wire, wye-connected transformer is 480 volts phase-to-phase, the phase to neutral voltage is ____________ volts.

2.

If the secondary of a four-wire, B phase high leg, delta connected transformer is 240 volts phase-to-phase, the phase-to-neutral voltage is ____________ volts A to neutral ____________ volts B to neutral ____________ volts C to neutral

3.

The term service section refers to the section of a switchboard which receives incoming power. The term ____________ ____________ equipment refers to equipment through which the power supply enters the building.

4.

According to NEC® Article 230.71, the maximum number of circuit breakers that can be used to disconnect and isolate the service from all other equipment is ____________ .

5.

A neutral ____________ ___________ is supplied in switchboards used as service entrance equipment to allow the branch neutral to be checked for continuity on the load side of the main disconnect.


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In addition to ensuring equipment is properly grounded, ground fault protection for people and equipment is also a concern. NEC® Article 230.95 states that ground-fault protection of equipment shall be provided for solidly grounded wye electrical services of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase for each service disconnecting means rated 1000 amperes or more. Although ground-fault protectors are not required on service disconnects that are less than 1000 amperes, depending on the installation, they still may be desirable. Ground fault interrupters designed to provide life protection must open a circuit at 5 milliamps (± 1 milliamp). Ground fault protection for equipment must open a circuit when ground fault current reaches 30 milliamps. Health care facilities, such as hospitals, require additional ground fault protection. This is outlined in NEC® Article 517.17. Direct Method

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One way a ground fault protector works is to install a sensor around one conductor, normally the neutral-to-ground strap. This is referred to as the direct method. When an unbalanced current from a line-to-ground fault occurs current will flow from ground to neutral. When the current reaches the setting of the groundfault sensor the shunt trip opens the circuit breaker, removing the load from the line.

Zero sequencing Method

Another way a ground fault protector works is with a sensor installed around all the circuit conductors, including the neutral on 4-wire systems. This is referred to as zero sequencing. During normal current flow the sum of all the currents detected by the sensor is zero. However, a ground fault will cause an unbalance of the currents flowing in the individual conductors. When this current reaches the setting of the ground-fault sensor the shunt trip opens the circuit breaker.

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Residual Method

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Separate sensors monitor current on all three phases (and the neutral on a 4-wire system. If the vectorial sum of the currents on the secondary of the sensors does not equal zero the breaker will be tripped.

Ground Fault Protection Devices

Ground fault protection is generally incorporated into a special type of protective device such as a molded case circuit breaker. Ground fault protection is also available in Siemens insulated case circuit breakers.

Ground fault protection can also be supplied on various disconnect switches, such as the bolted pressure switch.

Note: All main protective devices, except Vacu-Break® fusible switches, can be equipped with ground fault relays to comply with NEC® requirements.

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Switchboard Ratings

When selecting switchboards and overcurrent protection devices it is extremely important to know both the maximum continuous amperes and available fault current along with several other rating terms. Interrupting Rating

Interrupting rating refers to the current rating a protective device, such as a fuse or circuit breaker, can safely interrupt. Interrupting rating is also referred to as ampere interrupting capacity (AIC). NEC® article 110.9 states: Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current which is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.

Full Rating

There are two ways to meet this requirement. The full rating method is to select circuit protection devices with individual ratings equal to or greater than the available fault current. This means that, in the case of a building with 65,000 amperes of fault current available at the service entrance, every circuit protection device must be rated at 65,000 amperes interrupting capacity (AIC). Switchboards are available with short circuit withstand ratings up to 200,000 amps. However, a full-rated switchboard over 100,000 AIC can be expensive because of the necessary bus bracing.


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Series-Rated

A full-rated switchboard is not always required. Seriesrated switchboards are UL listed and are adequate for many applications at a lower cost. The series-rated concept is that the main upstream circuit protection device must have an interrupting rating equal to or greater than the available fault current of the system, but subsequent downstream circuit protection devices connected in series can be rated at lower values. This is permitted as long as the series combinations shown have been tested and certified by UL. For example, a building with 42,000 amperes of available fault current might have the breaker at the service entrance rated at 42,000 AIC and additional downstream breakers rated at 18,000 AIC.

Series-rated breaker combinations must be tested in series in order to be UL listed. Siemens series-rated breakers are listed in the UL “Recognized Components Directory” (yellow books) Volume 1. Selected series-rated breakers are listed in the Speedfax catalog. Your Siemens sales engineer can provide more information on Siemens series-rated circuit breakers. Keep in mind that it is the protection device mounted in the switchboard that interrupts current. Therefore, the interrupt rating applies to the protective devices. Withstand Rating

Short circuit withstand rating refers to the level of fault current a piece of equipment can withstand without sustaining damage. The standards for short circuit withstandability are set by Underwriters Laboratories (UL Standard 891). Bus structures and bracing are designed to withstand a specified amount of current for a specified amount of time. The short circuit withstand rating of a switchboard is determined by the combined withstand, interrupting, and current limiting capabilities of the bus, overcurrent protective devices in the switchboard, and any overcurrent protective devices within or ahead of the switchboard that may supply and protect it.

55

Ampere Rating

The ampere rating refers to the current a switchboard or protective device will carry continuously without deterioration and without exceeding temperature rise limits.

Voltage Rating

The voltage rating of a switchboard must be at least equal to the system voltage. The voltage rating of a switchboard can be higher than the system voltage, but never less. For example, a 480 VAC switchboard could be used on a 240 VAC system. A 240 VAC switchboard could not be used on a 480 VAC system.

Review 5

56

1.

Ground fault protection is required for grounded wye electrical services of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase when service disconnecting devices are rated at ____________ amps or more.

2.

All main protective devices except ____________ - ____ ________ ____________ ____________ can be equipped with ground fault relays.

3.

Ground fault protection is discussed in NEC® Article ____________ .

4.

____________ rating refers to the level of fault current a piece of equipment can withstand without sustaining damage.

5.

____________ rating refers to the maximum current a protective device such as a fuse or circuit breaker can safely interrupt.

6.

A switchboard is said to be ___________ - ____________ when the main upstream circuit protection device is equal to or greater than the available fault current, but subsequent downstream circuit protection devices connected in series are rated at a lower AIC.

7.

____________ ____________ refers to the current a switchboard or protective device will carry continuously without deterioration and without exceeding temperature rise limits.

SB1, SB2, and SB3 Switchboards

Siemens manufactures a variety of switchboards. The type of switchboard selected is determined by a variety of factors such as space, load, and environment. In addition to meeting present loads, the switchboard should be sized to accommodate reasonable future load additions. The continuous rating and through-bus can be sized on the basis of anticipated future load demand. Trip units or fuses of lower ratings can be installed to meet present load demands and changed in the future as load increases. Siemens switchboards are available in Type 1 (indoor) or Type 3R (outdoor) enclosures. SB1, SB2, and SB3 Sentron™ switchboards can be found in a variety of industrial plants, hospitals, and commercial buildings.

57

SB1 Switchboards

SB1 switchboards are designed to be used in an application where space is a consideration. SB1 switchboards are rear aligned. The service section can be deeper than the distribution sections. By aligning the rear the switchboard can be installed against a wall.

SB1 Ratings and Devices

The SB1 switchboard contains front-connected main protective devices and through-bus ratings up to 2000 amps at 480 VAC. SB1 switchboards are front accessible with front connected devices. Main devices, used in the service section, are available from 400 - 2000 amps. Branch devices, used in the distribution section, are available from 15 - 1200 amps.

58

SB2 Switchboards

The rear of SB2 switchboards align as standard. Front and rear alignment is available as an option. SB2 switchboards are front accessible and front connected. The following switchboard pictorial illustrates an SB2 that is front and rear aligned. In this example a pull section has been added to allow room to pull cable up from the bottom to connections in the top of the service section. Bottom feed without a pull section is also available. SB2 switchboards may be mounted against a wall.

SB2 Ratings and Devices

The SB2 contains through-bus ratings up to 4000 amps at 480 VAC. Main devices are available from 400 - 4000 amps. Branch devices are available from 15 - 1600 amps.

59

SB3 Switchboards

60

SB3 switchboards are front and rear aligned. SB3 switchboards are designed for special configurations, such as incoming and outgoing busway connections, and automatic transfer schemes. Through-bus ratings are available up to 6000 amps. Branch devices are available from 15 - 2000 amps (custom configurations with higher ratings are available).

RCIII Switchboards

The branch and feeder devices in the Siemens type RCIII switchboards are individually mounted. This mounting method requires access to outgoing cable terminations from the rear. Type RCIII switchboards are rear connected and require rear access. Bus bar extensions from the feeder devices are run back to the rear of the switchboard for easy access. RCIII switchboards are front and rear aligned. The following drawing illustrates a type RCIII switchboard with Siemens insulated case circuit breakers (ICCB) in the service and distribution sections.

61

Drawout or Fixed Mounting

62

Depending on the protective device, it may be either drawout or fixed mounted. Insulated case circuit breakers (ICCB), for example, may be drawout or fixed mounted. Vacu-break® fusible switches are fixed mounted.

Ratings

63

Super Blue Pennant Switchboards

The Super Blue Pennant™ switchboard is designed as a service entrance switchboard. The main service disconnect and distribution devices are contained in a single unit. The metering provisions meet EUSERC (an electrical standardization coalition) specifications. Super Blue Pennant switchboards are rated for 400, 600, or 800 amps with a circuit breaker main and 400 or 600 amps with a fusible Vacu-Break® switch main.

64

Metering Compartment

The metering compartment has provisions for mounting a utility meter on the door. Super Blue Pennant uses hot sequence metering. Incoming power is connected to the main lugs.

Service Disconnect

The service disconnect can be a fusible Vacu-Break switch through 200,000 AIC, or a circuit breaker with a maximum rating of 65,000 AIC at 240 volts and 35,000 AIC at 480 volts.

Distribution Panel

Distribution kits are optional and field adaptable with ratings of 400 - 800 amps. Up to 40 branch circuit provisions are available with an 18 branch circuit minimum.

65

Commercial Metering Switchboards

Commercial metering switchboards are designed for commercial applications where multi-metering is required. These applications include shopping centers, office buildings, and other commercial buildings with multiple tenants. Type SMM Switchboards

66

Type SMM switchboards are designed to meet west coast utility and EUSERC specifications. The switchboard main service is rated up to 4000 amps at 480 volts. Service mains can be circuit breakers (up to 2000 amps), insulated case circuit breakers (up to 3000 amps), bolted pressure switches (up to 4000 amps), or Vacu-Break®, and HCP fusible switches (up to 1200 amps). Tenant mains, rated at 100 and 200 amps, are interchangeable. Tenant mains can be circuit breakers, fusible switches, or T-fuse pullouts. The bus is braced for 65,000 amps. Higher bracing is available as an option. Metering sockets are rated for 200 amps continuous duty. The SMM switchboards incorporate a ring type meter cover design. The meter ring must be removed to disengage the meter from the socket. The meter cover does not have to be removed. Test blocks are standard equipment. The Type SMM switchboard shown below has a thru-main section.

Type MMS Switchboards

The MMS switchboard is similar to the SMM, however, it is not designed to meet west coast specifications. The main service is rated up to 4000 amps. Service mains can be circuit breakers (up to 2000 A), insulated case circuit breakers (up to 4000 A), bolted pressure switches (up to 4000 A), or Vacu-Break fusible switches (up to 1200 A). Tenant mains, rated at 100 and 200 amps, are interchangeable. Tenant mains can be circuit breakers, fusible switches, or T-fuse pullouts. All meter sockets are rated at 200 amps. Wiring is for 100 amps or 200 amps, depending on the tenant main device. Depending on the tenant main device, MMS switchboards are available with 2, 3, 4, or 6 sockets. The bus is braced for 50,000 amps. Higher bracing is available as an option. Type MMS switchboards incorporate a ringless type meter cover design. The meter cover has to be removed before the meter can be disengaged from the meter socket. Manual bypass is standard equipment.

67

Speciality Service Entrance Switchboards

Specialty service entrance switchboards can be used in various applications. A specialty service entrance switchboard may, for example, be placed ahead of a main switchboard. The specialty switchboard serves as the disconnect for the main switchboard. Specialty service entrance switchboards are available with a single molded case circuit breaker, Vacu-Break® fusible switch, or bolted pressure switch (not shown).

68

BCT Service Cubicle

BCT service cubicles use molded case circuit breakers. They are available in current ratings from 400 - 1200 amps. BCT specialty service entrance switchboards use cold sequence metering as standard and are top fed. For hot sequence metering the unit and circuit breaker can be inverted.

69

SCT Service Cubicle

SCT service cubicles use Vacu-Break® fusible switches. They are available with the following current ratings: 120/240, 480 Y/277 volts 208 Y/120, 240, 480, 600 volts 208 Y/120, 240 volts

400, 600, and 800 amps 600 and 800 amps 800 and 1200 amps

SCT service cubicles use cold sequence metering. Hot sequence metering is available.

70

Enclosed Bolted Pressure Switch

Enclosed bolted pressure switch specialty switchboards can be used when metering is not required and are available with top or bottom feed. The following drawing illustrates a top feed enclosed bolted pressure switch. Current ratings are available from 800 - 4000 amps.

71

Information Needed To Order Switchboards

When ordering a switchboard several questions need to be answered. 1.

What are the power system specifications (voltage, phases, number of wires)?

2.

What is the AIC rating (ampere interrupting capacity)?

3.

Will full or series rated be required?

4.

What is the NEMA Type enclosure desired?

5.

How many circuits are required?

6.

What types of overcurrent protective devices (MCCB, ICCB, Vacu-Break® fusible switch, bolted pressure switch) are required?

7.

Does the switchboard need to be suitable for service entrance?

8.

What amperage is the switchboard rated at?

9.

Will the switchboard be top or bottom fed?

10. Will the switchboard be hot or cold metering? 11.

What will the alignment be?

12. What type of bus material is required (temperature/ density)? 13. What special modifications are needed (serial communications, pull sections, corner sections)?

72

Review 6 1.

SB1 switchboards are ____________ aligned.

2.

The maximum main bus rating of an SB1 switchboard is ____________ amps.

3.


4.


5.

Super Blue Pennant switchboards are rated up to ____ ________ amps with a circuit breaker and ____________ amps with a Vacu-Break® fusible switch.

6.

Up to ____________ branch circuit provisions are available in the distribution panel of the Super Blue Pennant switchboard.

7.

The type of commercial metering switchboard used on the west coast is Type ____________ .

8.

The type of specialty service entrance switchboard that uses a molded case circuit breaker as a main disconnect is a Type ____________ service cubicle.

9.

The type of specialty service entrance switchboard that uses a Vacu-Break fusible switch as a main disconnect is a Type ____________ service cubicle.

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Review Answers

Review 1

1) 120; 2) 277; 3) 100; 4) NEMA, UL; 5) 408.

Review 2

1) ampacity; 2) Time; 3) 200,000; 4) 90; 5) bus; 6) Splice; 7) through-bus.

Review 3

1) service, distribution; 2) pull box; 3) pull section; 4) 4300; 5) Hot sequence; 6) Cold sequence; 7) f; 8) distribution; 9) Rear aligned.

Review 4

1) 277; 2) 120, 208, 120; 3) service entrance; 4) six; 5) disconnect link.

Review 5

1) 1000; 2) Vacu-Break fusible switches; 3) 230.95; 4) Withstand; 5) Interrupting; 6) series-rated; 7) Ampere rating.

Review 6

1) rear; 2) 2000; 3) 4000; 4) 6000; 5) 800, 600; 6) 40; 7) SMM; 8) BCT; 9) SCT.

74

Final Exam

The final exam is intended to be a learning tool. The book may be used during the exam. A tear-out answer sheet is provided. After grading the test, mail the answer sheet in for grading. A grade of 70% or better is passing. Upon successful completion of the test a certificate will be issued. 1.

The requirements for switchboards are covered in NEC® Article ____________ . a. c.

2.

overloads and heat overloads and short circuits short circuits and heat ground fault and heat

10,000 100,000

b. d.

50,000 200,000

The standard height of a Siemens switchboard is ____________ inches. a. c.

5.

318 770

The AIC rating of a Class R fuse is ____________ amps. a. c.

4.

b. d.

Two causes of overcurrent are ____________ . a. b. c. d.

3.

210 408

32 72

b. d.

38 90

The correct NEMA phase sequence for a vertical bus, as viewed from the front, left to right is ____________ . a. c.

A-B-C C-A-B

b. d.

A-C-B C-B-A

75

6.

Two adjoining switchboard sections are connected together with ____________ . a. c.

7.

pull section distribution section

Hot sequence Top feed

b. d.

Cold sequence Bottom feed

front front and rear

b. d.

rear front or rear

138 277

b. d.

240 480

On a three-phase, four-wire, B phase high leg, delta-connected transformer the high leg is ____________ . a. c.

76

b. d.

On a three-phase, four-wire, wye-connected transformer with a secondary voltage of 480 volts phase-to-phase, the phase-to-neutral voltage is ____________ volts. a. c.

11.

service section pull box

A switchboard with a service section that is deeper than the distribution section would be ____________ aligned. a. c.

10.

compression lugs cross bus

____________ is when power is still applied to the utility meter when the service main is switched off. a. c.

9.

b. d.

A ____________ is used when cables fed from the bottom of a switchboard need to be routed to the top of the switchboard. a. c.

8.

vertical bus bars splice plates

A-N C-N

b. d.

B-N A-B

12.

The maximum number of switches or circuit breakers used to disconnect and isolate the service from all other equipment on service-entrance equipment is ____________ . a. c.

13.

always rarely

b. d.

never often

Molded case circuit breakers Vacu-Break fusible switches Insulated case circuit breakers Bolted pressure switches

The ____________ is a removable link that isolates the neutral bus from, the grounded neutral bus. a. b. c. d.

16.

2 6

All main protective devices, except ____________ , can be equipped with ground fault relays to comply with NEC® requirements. a. b. c. d.

15.

b. d.

The neutral conductor is ____________ grounded at the service-entrance switchboard. a. c.

14.

1 4

neutral disconnect link ground bus bar vertical neutral bus horizontal neutral bus

Article 230.95 of the NEC® states that ground-fault protection of equipment shall be provided for solidly grounded wye electrical services of more than 150 volts to ground, but not exceeding 600 volts phase-tophase for each service disconnecting means rated ____________ amperes or more. a. c.

5 milliamps 1000 amps

b. d.

10 amps 200,000 amps

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17.

The rating which refers to the level of short circuit fault current a piece of equipment can withstand without sustaining damage is the ____________ rating. a. c.

18.

1200 4000

b. d.

2000 6000

1200 3000

b. d.

2000 5000

Super Blue Pennant switchboards are rated up to ____________ amps with a fusible Vacu-Break switch main. a. c.

78

full withstand

The maximum rating for an insulated case circuit breaker used as a main device for an RCIII switchboard is ___________ amps. a. c.

20.

b. d.

The SB2 contains through-bus ratings up to ___________ amps. a. c.

19.

interrupting ampacity

600 1200

b. d.

800 2000

Notes

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Siemens E book

Siemens Schuckert D-III

Judaism, The e-Book

E Book Kidnap 1

Flower Crochet e-Book

Zeit zu leben E-Book

E Book Eva S Dochters

The Hollows - E-book Extras

Siemens Schuckert D III&IV

Heart Of Darkness E-book

The Secret Sharer E-book

Che cos'e e come funziona un E-book

SIMATIC HMI. WinCC V6.0. Опции - Siemens AG

Odd and the Frost Giants (e-book)

(e-book)Stephen King-The Shining

(e-book)Tom Clancy-Executive Orders

A. E. Van Vogt - Book Of Ptath

(e-book)Tom Clancy-Red Storm Rising

E-Book - Tom Clancy - Armored Cav

E-Book - John Grisham - The Summons

(e-book)Stephen King-Bag of Bones

Corel Draw 10 Learning e-Book

(e-book) - Dean Koontz - Winter Moon (1)

(e-book)Isaac Asimov-Fantastic Voyage II

E. E

SIMATIC HMI. WinCC V6. Основная документация - Siemens AG

E

E)

E

e

E

Siemens E book

Siemens Schuckert D-III

Judaism, The e-Book

E Book Kidnap 1

Flower Crochet e-Book

Zeit zu leben E-Book

E Book Eva S Dochters

The Hollows - E-book Extras

Siemens Schuckert D III&IV

Heart Of Darkness E-book

The Secret Sharer E-book

Che cos'e e come funziona un E-book

SIMATIC HMI. WinCC V6.0. Опции - Siemens AG

Odd and the Frost Giants (e-book)

(e-book)Stephen King-The Shining

(e-book)Tom Clancy-Executive Orders

A. E. Van Vogt - Book Of Ptath

(e-book)Tom Clancy-Red Storm Rising

E-Book - Tom Clancy - Armored Cav

E-Book - John Grisham - The Summons

(e-book)Stephen King-Bag of Bones

Corel Draw 10 Learning e-Book

(e-book) - Dean Koontz - Winter Moon (1)

(e-book)Isaac Asimov-Fantastic Voyage II

E. E

SIMATIC HMI. WinCC V6. Основная документация - Siemens AG

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E)

E

e

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