Energy-Efficient Electric Motors and Their Applications. Second Edition

Transcription

1 Energy-Efficient Electric Motors and Their Applications Second Edition

2 Energy-Efficient Electric Motors and Their Applications Second Edition Howard E. Jordan Springer Science+ Business Media, LLC

3 Library of Congress Cataloging in Publication Data Jordan, Howard E. Energy-efficient electric motors and their applications / Howard E. Jordan. 2nd ed. p. cm. Includes bibliographical references and index. ISBN Electric motors Energy consumption. 2. Electric power Conservation. I. Title. TK2781.J dc CIP The first edition of this volume was published by Van Nostrand Reinhold in It is now out of print. ISBN ISBN (ebook) DOI / Springer Science+Business Media New York Originally published by Plenum Press, New York in 1994 Softcover reprint of the hardcover 1st edition 1994 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher

4 Preface The worldwide energy shortage has had a significant impact on the design and application of electric motors. The opportunity is now available, as never before, to select motors which can result in substantial energy savings. Wise selection and use of energy-efficient motors not only supports our national energy conservation goal but also provides attractive financial rewards to the motor user. This book is dedicated to providing the technological background and understanding for selecting and using electric motors to accomplish their mission with minimum energy consumption. Many motor manufacturers now offer energy-efficient lines of motors with the result that motor buyers now have two distinct categories of products from which to select: standard and energy-efficient motors. However, not all applications can profit from the use of energy-efficient motors. In fact, there are some applications in which an energy-efficient motor will perform less satisfactorily than a less efficient type of motor. In certain applications, the energy-efficient variety will not even provide the necessary driving capability. The plant engineer, engineering consultant, installing contractor, or other faced with the problem of selecting a motor or replacing an existing motor is left in a quandary. Should he use an energy-efficient motor or not? Ifhe does, will he save money? What other characteristics will be affected? People faced with these decisions are usually not specialists in electric motor technology. This book provides a guide to answering these questions in a form usable to engineers and contractors, as well as to others who do not specialize in motor technology. v

5 vi Preface A U.S. Department of Energy study has identified the horsepower range of induction motors as the segment in which almost one-half of all motor-drive energy is used. This segment, therefore, offers the greatest potential for energy savings. This book is primarily directed toward polyphase induction motors, but some discussion is included on other types, namely single-phase, excited-field synchronous, and synchronous-reluctance machines. An entire section (6.4) has been devoted to the permanent-magnet synchronous motor in this Second Edition. This type of motor has become increasingly popular in recent years. Section 6.4 explains why and provides information on the types of permanent magnets used, the performance characteristics of these machines, and the applications where permanent-magnet motors are in use. Chapter 7 is devoted to adjustable-speed motor drives. Adjustablespeed drives are widely used to control speed, tension, position, etc. for industrial processes. In addition to serving a broad range of control applications, adjustable-speed drives can also provide an energy-savings benefit relative to constant-speed motors for certain applications. These energy-savings considerations are discussed in Chapter 7. Chapter 7 also describes several of the more important types of electronic controls used to provide the adjustable-speed function. This discussion starts with the phase-controlled dc drive and then describes several types of inverters and brushless dc drives. The chapter provides a technical background which is useful in deciding whether or not to use adjustable speed or constant speed. If adjustable speed is the choice, the technical information on various types of drives will be useful in selecting the proper type. The era of the energy-efficient motor has arrived. Energy consumption is a parameter which needs to be considered in each motor selection and application situation. This book has been written to help in making this decision wisely. Cleveland, Ohio Howard E. Jordan

6 Contents 1. INTRODUCTION Need for Energy-Efficient Motors Energy Usage Profile Types of Electric Motors and Their Energy-Saving Potential TECHNOLOGY OF ENERGY-EFFICIENT MOTORS Energy Usage in Motor Applications Five Components of Motor Losses Calculation of Loss Reduction Economic Payback Calculations SELECTION AND APPLICATION OF ENERGY- EFFICIENT MOTORS Applications Which Can Benefit Most from Energy-Efficient Motors Matching the Motor to the Load Applications Which Do Not Benefit from Energy-Efficient Motors Replacement versus Repair Multispeed Motors Load Shedding Saves Energy Calculation of Acceleration Losses when Retarding Load Torque Is Present Unbalanced Voltage Other Unusual Service Conditions Keeping Motors Running vii

7 viii Contents 4. EFFICIENCY LABELING AND VERIFICATION Variations in Motor Efficiency Efficiency Labeling Testing ofinduction Motors International Testing Standards for Motors S. POWER FACTOR Power Factor and Its Effect on Energy Consumption Power Factor Penalty Cost Example Power Factor Correction Calculation of Power Factor Correction KVAC Self-Excitation ofinduction Machines SINGLE-PHASE AND SYNCHRONOUS MOTORS.... 9S 6.1. Single-Phase Motor Types Energy-Efficient, Single-Phase Motors Synchronous Motors, Excited-Field Type Permanent-Magnet Synchronous Motors ADJUSTABLE-SPEED DRIVES Adjustable Speed Applied to Pumps and Fans dc Drives ac Drives-Inverters Transistor Pulse-Width-Modulated Inverters Load-Commutated Inverter Drive Frequency-Voltage Relationships and Starting for Motors Used with Adjustable-Speed Drives Harmonics and Their Effect on Motor Losses Brushless dc Motors and Drives ac MOTOR CONTROL AND PROTECTION: STARTING, RUNNING PROTECTION, AND SURGE PROTECTION. lsi 8.1. Overview of Starting Requirements and Controls Across-the-Line Starting Primary-Impedance Starting Autotransformer Starting Wye-Delta Starting Part-Winding Starting

8 Contents ix 8.7. Solid-State, Electronic Starting Synchronous Motor Starting Motor Overtemperature Protection Methods Inherent-Overheating Protective Devices Overload Relays Thermostats Embedded Temperature Detectors Solid-State Protection Surge Protection INDEX