Electric Motor Control Electric Motor Control

9th Edition

Stephen L. Herman

Electric

Motor

Control

Electric

Motor

Control

This page intentionally left blank

9th Edition

Australia • Canada • Mexico • Singapore • Spain • United Kingdom • United States

Stephen L. Herman

Electric

Motor

Control

Electric

Motor

Control

Electric Motor Controls, Ninth Edition

Stephen L. Herman

Vice President, Career and Professional

Editorial: Dave Garza

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© 2010, 2007 Delmar, Cengage Learning

ALL RIGHTS RESERVED. No part of this work covered by the copyright

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except as permitted under Section 107 or 108 of the 1976 United States

Copyright Act, without the prior written permission of the publisher.

Library of Congress Control Number: 2009925275

ISBN-13: 978-1-4354-8575-4

ISBN-10: 1-4354-8575-0

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Publisher does not warrant or guarantee any of the products described

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v

Preface vi

Section 1 Introduction 1

UNIT 1 General Principles of Electric Motor Control 3

UNIT 2 Fractional and Integral Horsepower Manual Motor Starters 17

UNIT 3 Magnetic Line Voltage Starters 23

Section 2 Circuit Layout, Connections, and Symbols 49

UNIT 4 Symbols 51

UNIT 5 Interpretation and Application of Simple Wiring

and Elementary Diagrams 63

Section 3 Control Pilot Devices 79

UNIT 6 Push Buttons and Control Stations 81

UNIT 7 Relays 87

UNIT 8 Contactors 95

UNIT 9 Timing Relays 103

UNIT 10 Pressure Switches and Regulators 113

UNIT 11 Float Switches 117

UNIT 12 Flow Switches 123

UNIT 13 Limit Switches and Proximity Control 127

UNIT 14 Phase Failure Relays 135

UNIT 15 Solenoid Valves 139

UNIT 16 Temperature Switches 143

Section 4 Basic Control Circuits 147

UNIT 17 Two-Wire Controls 149

UNIT 18 Three-Wire and Separate Controls 153

UNIT 19 Hand-Off Automatic Controls 159

UNIT 20 Multiple Push-Button Stations 163

UNIT 21 Interlocking Methods for Reversing Control 165

UNIT 22 Sequence Control 173

UNIT 23 Jogging (Inching) Control Circuits 181

UNIT 24 Time-Delay, Low-Voltage Release Relay 187

Contents

Section 5 AC Reduced Voltage Starters 191

UNIT 25 The Motor and Starting Methods 193

UNIT 26 Primary Resistor-Type Starters 199

UNIT 27 Autotransformer Starters 205

UNIT 28 Part Winding Motor Starters 211

UNIT 29 Automatic Starters for Star-Delta Motors 217

UNIT 30 AC Solid-State Reduced Voltage Controller 223

Section 6 Three-Phase, Multispeed Controllers 231

UNIT 31 Controllers for Two-Speed,Two-Winding (Separate Winding) Motors 233

UNIT 32 Two-Speed, One-Winding (Consequent Pole) Motor Controller 239

UNIT 33 Four-Speed,Two-Winding (Consequent Pole) Motor Controller 247

Section 7 Wound Rotor (Slip Ring) Motor Controllers 253

UNIT 34 Wound Rotor Motors and Manual Speed Control 255

UNIT 35 Push-Button Speed Selection 261

UNIT 36 Automatic Acceleration for Wound Rotor Motors 263

UNIT 37 Automatic Speed Control for Wound Rotor Motors 269

UNIT 38 Solid-State Adjustable Speed Controller for AC Wound Rotor Motors 275

Section 8 Synchronous Motor Controls 279

UNIT 39 Synchronous Motor Operation 281

UNIT 40 Push-Button Synchronizing 287

UNIT 41 Timed Semiautomatic Synchronizing 291

UNIT 42 Synchronous Automatic Motor Starter 295

Section 9 Direct-Current Controllers 303

UNIT 43 About DC Motors 305

UNIT 44 Use of Reduced Voltage for Starting 311

UNIT 45 Across-the-Line Starting 315

UNIT 46 Compensating and Definite Time Control Starting 319

UNIT 47 Solid-State Adjustable Speed Control 325

vi

Section 10 Methods of Deceleration 333

UNIT 48 Plugging 335

UNIT 49 Electric Brakes 343

UNIT 50 Dynamic and Regenerative Braking 347

UNIT 51 Electric and Electronic Braking 353

Section 11 Motor Drives 361

UNIT 52 Direct Drives and Pulley Drives 363

UNIT 53 Gear Motors 369

UNIT 54 Variable-Frequency Mechanical Drives 373

UNIT 55 AC Adjustable Frequency Drives 377

UNIT 56 Magnetic Clutch and Magnetic Drive 385

UNIT 57 DC Variable-Speed Control—Motor Drives 391

UNIT 58 Programmable and Motion Control 397

Section 12 Troubleshooting 413

UNIT 59 Motor Startup and Troubleshooting Basics 415

UNIT 60 Troubleshooting Techniques 427

APPENDIX A Motor Types and Line Diagrams 441

APPENDIX B Power Supplies 443

GLOSSARY 445

INDEX 453

vii

Electric Motor Control provides beginning students with a practical

approach to motor control. The textbook discusses electrical and mechanical

components and how they are connected to control different types of motors.

Many different types of control circuit and illustrations are discussed. The text

contains a wealth of practical information that will apply to almost any indus￾trial application.

PREREQUISITES AND USE

The text assumes that students have knowledge of basic electrical theory

and common series and parallel circuits. Electric Motor Control has been used

successfully for both formal classroom training and self study. It is used exten￾sively in preapprentice and indentured apprentice training programs and in

organized journeyman electrician classes. The practical approach to motor

control makes this a very useful handbook on the job for installing, monitor￾ing, and maintaining control systems.

MAJOR FEATURES

Electric Motor Control provides a very practical approach to a somewhat dif￾ficult subject. The text is written in easy-to-understand language. Each unit of

instruction covers a short, concise topic. Expected student learning is outlined

in the objectives at the beginning of each unit. The appendices and glossary

provide further explanation of terms and servicing to troubleshooting, which

the student is encouraged to use. The ninth edition contains expanded infor￾mation on overload relays and numerous updated illustrations. The text

employs a second color to highlight important concepts. The ninth edition pro￾vides an update to a textbook that has long been regarded as an outstanding

book on the subject of motor control theory and practical application.

PRACTICAL APPROACH TO PROBLEM SOLVING

Electric Motor Control illustrates control systems, starting with the sim￾plest of equipment, and builds on it in a step-by-step fashion to more complex

circuits. Students learn to draw and interpret motor control schematics and

wiring diagrams. The text helps teach students to think about the process

involved in drawing and reading control schematics. This approach leads stu￾dents in a natural progression into the basic concepts needed to install and

troubleshoot control systems.

SUPPLEMENTS TO THIS TEXT

An Instructor Resource CD is available for this text. It contains tools and

instructional resources that enrich your classroom and make your preparation

time shorter. The elements of the instructor resource link directly to the text

Preface

viii

and tie together to provide a unified instructional system. Features contained in

the instructor resource include:

• An Instructor Manual as a PDF file that contains answers to the end of

unit questions, a comprehensive test, and answers to the comprehensive test.

• Unit presentations created in PowerPoint(®): These slides provide the basis

for a lecture outline that helps you to present concepts and material.

• Test Questions: More than 250 questions of varying levels of difficulty are

provided in true/false and multiple choice formats. These question scan be

used to assess student comprehension or can be made available to the stu￾dent for self-evaluation.

ISBN: 1435485742

ix

ACKNOWLEDGMENTS

The author and staff at Delmar Cengage Learning wish to express their

appreciation to the instructors who reviewed the previous edition and ninth

edition revision plan and made suggestions for improvements.

Michel Benzer

Bluegrass Community and Technical College

Lexington, KY

Mark Bohnet

Northwest Iowa Community College

Sheldon, IA

Kevin Boiter

Piedmont Technical College

Greenwood, SC

John L. Brown

Portland Community College

Portland, OR

Michael Brumbach

York Technical College

Rock Hill, SC

John Everett

East Central Community College

Decatur, MS

Ivan Maas

North Dakota State College of Science

Wahpeton, ND

Marvin Moak

Hinds Community College

Raymond, MS

x

Introduction

1

SECTION

Unit 1 General Principles of

Electric Motor Control

Unit 2 Fractional and Integral Horsepower

Manual Motor Starters

Unit 3 Magnetic Line Voltage Starters

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UNIT 1

3

There are certain conditions that must be con￾sidered when selecting, designing, installing, or

maintaining electric motor control equipment.

The general principles are discussed to help

understanding and to motivate students by

simplifying the subject of electric motor control.

Motor control was a simple problem when

motors were used to drive a common line shaft

to which several machines were connected. It

was simply necessary to start and stop the

motor a few times a day. However, with individ￾ual drive, the motor is now almost an integral

part of the machine and it is necessary to de￾sign the motor controller to fit the needs of the

machine to which it is connected. Large instal￾lations and the problems of starting motors in

these situations may be observed in Figure 1–1

and Figure 1–2.

Motor control is a broad term that means any￾thing from a simple toggle switch to a complex

system with components such as relays, timers,

and switches.The common function of all controls,

however, is to control the operation of an electric

motor. As a result, when motor control equipment

is selected and installed, many factors must be

considered to ensure that the control will function

properly for the motor and the machine for which

it is selected.

MOTOR CONTROL INSTALLATION

CONSIDERATIONS

When choosing a specific device for a particu￾lar application, it is important to remember

that the motor, machine, and motor controller

are interrelated and need to be considered as a

package. In general, five basic factors influence

the selection and installation of a controller.

1. ELECTRICAL SERVICE

Establish whether the service is direct (DC)

or alternating current (AC). If AC, deter￾mine the frequency (hertz) and number of

phases in addition to the voltage.

Objectives

After studying this unit, the student should be able to:

• State the purpose and general principles of electric motor control.

• State the difference between manual and remote control.

• List the conditions of starting and stopping, speed control, and

protection of electric motors.

• Explain the difference between compensating and definite time

delay action.

General Principles of

Electric Motor Control

4 SECTION 1 INTRODUCTION

2. MOTOR

The motor should be matched to the electri￾cal service and correctly sized for the ma￾chine load in horsepower rating (hp). Other

considerations include motor speed and

torque. To select proper protection for the

motor, its full-load current rating (FLC),

service factor (SF), time rating (duty), and

other pertinent data—as shown on the

motor nameplate—must be used.

3. OPERATING CHARACTERISTICS OF

CONTROLLER

The fundamental tasks of a motor con￾troller are to start and stop the motor and

to protect the motor, machine, product, and

operator. The controller may also be called

upon to provide supplementary functions

such as reversing, jogging or inching, plug￾ging, or operating at several speeds or at re￾duced levels of current and motor torque

(see Glossary). Section 430 of the National

Electrical Code® (NEC®) provides require￾ments concerning the installation of motor

circuits. This section is employed to deter￾mine the proper conductor size, overload

size, and short circuit protection rating

for motor installations. In some industries

electrical engineers are responsible for de￾termining the requirements for installing

a motor or motors. In other industries the

electrician is expected to perform this task.

4. ENVIRONMENT

Controller enclosures serve to provide

safety protection for operating personnel

by preventing accidental contact with live

parts. In certain applications, the con￾troller itself must be protected from a vari￾ety of environmental conditions, which

might include

■ Water, rain, snow, or sleet

■ Dirt or noncombustible dust

■ Cutting oils, coolants, or lubricants

Both personnel and property require protec￾tion in environments made hazardous by the

Fig.1–1 Five 2000 hp,1800 rpm induction motors driving water pumps for a Texas oil/water operation.Pumps are used

to force water into the ground and “float” oil upward.(Courtesy of Electric Machinery Company,Inc.)

Fig. 1–2 Horizontal 4000 hp synchronous motor dri￾ving a large centrifugal air compressor.(Courtesy of Electric

Machinery Company,Inc.)