TRANSFORMERS AND ROTATING MACHINES - Springer

1 ~ TRANSFORMERS AND ROTATING MACHINES TRANSFORMERS AND ROTATING MACHINES ~~-1~& The City College of the City University of New York ~ Springer SCIENCE+BUSINESS MEDIA, LLC Van Nostrand Reinhold Company Regional Offices: New York Cincinnati Atlanta Dallas San Francisco Van Nostrand Reinhold Company International Offices: London Toronto Melbourne Library of Congress Catalog Card Number: 78-18398 ISBN 978-94-017-1396-2 ISBN 978-94-017-1394-8 (eBook) DOI All rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means-graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage and retrieval gystems-without permission of the publisher. Manufactured in the United States of America 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Library of Congress Cataloging in Publication Data Stein, Robert.

2 electric power gystem components. Includes index. 1. electric machinery. 2. electric TRANSFORMERS . I. Hunt, William Thomas. II. Title. '4 78-18398 Copyright 1979 by Springer Science+Business Media New YorkOriginally published by Litton Educational Publishing, Inc. in 1979 Softcover reprint of the hardcover 1st edition 1979 Preface There are good reasons why the subject of electric power engineering, after many years of neglect, is making a comeback in the undergraduate curriculum of many electrical engineering departments. The most obvious is the current public awareness of the "energy crisis." More fundamental is the concern with social responsibility among college students in general and engineering students in particular. After all, electric power remains one of the cornerstones of our civilization, and the well-publicized problems of ecology, economy, safety, dependability and natural resources management pose ever-growing challenges to the best minds in the engineering community.

3 Before an engineer can successfully involve himself in such problems, he must first be familiar with the main components of electric power systems. This text-book will assist him in acquiring the necessary familiarity. The course for which this book is mainly intended can be taken by any student who has had some cir-cuit analysis (using discrete elements, and including sinusoidal steady state) and elementary electromagnetic field theory. Most students taking the course will be in their junior or senior years. Once the course is completed, students may decide to go more deeply into the design and operation of these components and study them on a more advanced level, or they may direct their attention to the problems of the system itself, problems which are only hinted at briefly at various points herein.

4 Quite a few of the subjects covered here have been known and described by earlier writers. In fact, the older textbook literature in this field constitutes a valuable heritage. Nevertheless, and contrary to widespread belief, there also have been great changes in the practice of electric power engineering in recent years. Moreover, the electrical engineering students for whom this text is largely written bring a changed background of prerequisite training and knowledge to this study. All these changes call for a completely fresh start, not just a patch-work of adjustments and insertions to "update" obsolete treatments. The authors, who have devoted half a lifetime to the teaching of this subject, have given much thought to the changing scene in electric power engineering and to the changing needs of their students.

5 Some of the principles used in writing this text are given below. a. To be at the right level for its readers, a textbook must be understandable y vi PREFACE to less-gifted students and yet be challenging enough to hold the interest of top-rated students. b . An intelligent reader wants more than mere facts. He asks for explanations of such facts, for the logic behind them and the connections between them. A textbook should satisfy and encourage this attitude as much as possible. c. Beware of time-honored traditions! It is true that many such traditions have earned respect because of their excellence, but many faulty explanations and illogical sequences have been perpetuated through generations of textbook authors. On the whole, it may be said that the more widely accepted the treat-ment of a subject, the more it should be scrutinized with suspicion before it is adopted.

6 D. In the past 10 to 20 years, the most significant change affecting electric power engineering has been the ascendency of electronic controls. This topic must be integrated into the text, appearing wherever it is pertinent, not just in an added chapter or appendix. e. On the other hand, the digital computer, while having revolutionized the actual operation of power systems, as well as the design of their components, has only a minor influence on the basic theory and the understanding of these components. f. The basic aim of this book is to impart to the reader an understanding of practical devices, not to give him additional practice in the use of the mathemat-ical tools of linear systems theory or to preempt the teaching of related subjects such as control systems engineering. The first two chapters are intended as an introduction, to clarify the purpose of the devices to be studied and the laws of nature on which their operation is based.

7 As far as the further choice and sequence of subjects is concerned, magnetic circuits are a necessary prerequisite to all the devices to be studied, and among those, it is logical and helpful to analyze TRANSFORMERS before ROTATING MACHINES . Two chapters {7 and 8) serve as a transition from TRANSFORMERS to motional devices. All the basic types of motors and generators are covered, with two or more chapters devoted to the more important ones. At the end of most chapters, there are sections containing illustrative examples and practice problems. Answers to problems are given at the end of the book. Our thanks are due to the Department of Electrical and Computer Engineering of the University of Massuchusetts in Amherst, for making the facilities of the University available. ROBERT STEIN WILLIAM T.}

8 HUNT, JR. Contents Preface v 1. The electric Power System 1 electric power and its competitors -Power system components - The need for TRANSFORMERS - A word about reliability - The quality of service -Power losses 2. Faraday's Induction Law 10 A little history - Flux and flux linkages - Transformer voltages and motional voltages -Self-and mutual inductances revisited 3. Magnetic Circuits 15 Ampere's law - Iron cores - Saturation -Series magnetic circuits -Parallel branches - Air gaps - Saturation curves -Examples -Problems 4. Sinusoidal Steady State 36 Review - Hysteresis - Energy storage -Core losses -Wave shapes and equivalent circuits - Examples -Problems 5. TRANSFORMERS 56 The ideal transformer-Imperfections-Sinusoidal steady-11tate equa-tions - The basic equivalent circuit - A choice of equivalent circuits -Voltage regulation - Efficiency - A look at design principles - Testing -Normalized quantities-An alternative: mutual inductance-Examples-Problems 6.

9 Transformer Connections 89 Autotransformers - Single-phase power - Review of three-phase circuits - Three-phase power - Transformation of three-phase power - Examples -Problems 7. Electromechanical Energy Conversion 110 Motional voltages - Generator action - Motor action -Singly excited devices - Linear analysis - ROTATING motion - Torques in multiply excited devices -Salient and non-salient poles -Examples -Problems vii viii CONTENTS 8. Distributed Windings 142 Flux distribution-The mmfwave concept-Number of poles-The flux per pole - Motional voltages in ROTATING MACHINES - Winding factors -The electromagnetic torque - The ROTATING field - Examples -Problems 9. Three-phase Synchronous MACHINES 176 Field excitation - Stator and rotor - Synchronous speed - The addition of mmf waves-Operating conditions-Linear analysis-Open-and short-circuit characteristics -Normalized quantities -Examples -Problems 10.

10 Synchronous Motors 199 The infinite bus - Steady-state operation - The torque angle -l> as a space angle-Transient conditions-Analytical approach-Damping-Stability - Analytical study of transient stability - Methods of controlling field current - Examples -Problems 11. Synchronous Generators 230 The load-Steady-state operation-Voltage regulation-Power system operation - Generator and infmite bus - Synchronous reactors -Power losses and efficiency - Stability - electric transient phenomena -Brush-less excitation for a large alternator - Examples -Problems 12. Synchronous MACHINES With Salient Poles 254 Devices and models - Direct axis and quadrature axis - Synchronous reactance for salient-pole MACHINES -Phasor diagrams - Torque and torque angle - Reluctance motors - Inductances - Transformation of variables - Examples -Problems 13.