M.G. Say - Alternating Current Machines

M.G. Say

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Alternating

Current

Machines

M. G. SAY

Ph.D., M.Sc., A.C.G.I., D.I.C, F.I.E.E., F.R.S.E.

Emeritus Professor of Electrical Engineering Heriot-Watt University, Edinburgh

Fourth Edition

Pitman

PITMAN PUBLISHING LIMITED

39 Parker Street, London WC2B 5PB

Associated Companies

Copp Clark Ltd, Toronto

Fearon-Pitman Publishers Inc, Belmont, California Pitman Publishing New Zealand Ltd, Wellington Pitman Publishing Pty Ltd, Melbourne

M. G. Say 1976

First published in Great Britain 1976 Reprinted 1978

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All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise without the prior written permission of the publishers. This book may not be lent, resold, hired out or otherwise disposed of by way of trade in any form of binding or cover other than that in which it is published, without the prior consent of the publishers. This book is sold subject to the Standard Conditions of Sale of Net Books and may not be resold in the UK below the net price.

Text set in 10/11 pt IBM Press Roman, printed by photolithography and bound in Great Britain at The Pitman Press, Bath

ISBN 0 273 36197 X

Contents

Preface X1

2 Magnetic Circuits 26

2.1 Magnetic circuit properties 26

2.2 Magnetic materials 30

2.3 Magnetic circuit calculation 32

2.4 Transformer magnetic circuits 32

2.5 Machine magnetic circuits 37

2.6 Total flux 43

2.7 Leakage flux effects in transformers 44

2.8 Leakage flux effects in machines 50

2.9 Phase reactance 58

2.10 Unbalanced magnetic pull 59

2.11 Open magnetic circuits 61

3 Windings g3

3.1 Materials 53

3.2 Eddy currents 66

3.3 Electromotive force 72

3.4 Transformer windings 78

3.5 D.C. field windings 80

3.6 A.C. armature windings 81

3.7 Single-layer windings 86

3.8 Double-layer windings 87

3.9 Fractional-slot windings 89

3.10 Types of double-layer winding 91

3.11 Choice of winding 92

3.12 E.M.F. of windings 94

3.13 Tooth harmonics 103

3.14 Magnetomotive force of windings 107

4 Loss Dissipation 113

4.1 Dissipation of heat 113

4.2 Ideal temperature-rise/time relation U3

4.3 Cooling of small units 116

4.4 Cooling of large units 12fj

4.5 Heat transfer 128

4.6 Flow of coolant in transformers 133

4.7 Limits of temperature-rise 136

4.8 Thermal rating of transformers 138

4.9 Thermal rating of machines 140

5 Transformers: Theory and Performance 142

5.1 Theory of the power transformer 142

5.2 Power transformer on load 146

5.3 Losses and efficiency 147

5.4 Regulation 150

5.5 Operational equivalent circuits 152

5.6 Vibration and noise 154

5.7 Harmonics 154

5.8 Transients 159

5.9 Three-phase connections 166

5.10 Three/two and three/one-phase connections 169

5.11 Autoconnection 171

5.12 Three-winding connection 173

5.13 Zero-phase-sequence impedance 177

5.14 Tap-changing 179

5.15 Parallel operation 182

5.16 Cooling methods 186

5.17 Protection 187