Alternating Current Machines

555 Pages·2013·11.43 MB·English

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A PITMAN INTERNATIONAL TEXT
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Alternating
Current
Machines
SAY
M. G.
Ph.D., M.Sc., A.C.G.I., D.I.C, F.I.E.E., F.R.S.E.
EmeritusProfessorofElectricalEngineering
Heriot-WattUniversity,Edinburgh
Fourth Edition
Pitman
PITMANPUBLISHINGLIMITED
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 publishedinGreat Britain 1976
Reprinted 1978
^io„uaea.
ME ROPOLlTAN
BOROUGH OF WIGAN
DEPT. OF LEISURE
LIBRARIES
1 Op. ur. ^'-jo/jrji U?
1
Ace. No.
Date Wwi<\ ITS*
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Clas- Mo waa. i>ȣ2>
All rights reserved. No part ofthispublicationmaybe reproduced, stored
ina retrieval system, ortransmitted,in any form orby anymeans,elec-
tronic,mechanical, photocopying, recordingand/orotherwisewithout
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Conditions ofSale ofNet Booksandmay not be resoldinthe UKbelow
the net price.
Text set in 10/11 pt IBMPress Roman, printedby
photolithography andboundin Great Britain at The
Pitman Press, Bath
ISBN 273 36197 X
Contents
Preface X1
1 1ntroductory
1.1 Alternating-current machines 1
1.2 Performance 2
1.3 Design 3
1.4 Methods ofapproach 5
6
1.5 Basic principles
1.6 Basic forms 8
1.7 Conventions 9
1.8 Dynamic circuit theory 13
1.9 Prototype ideal transformer 13
1.10 Prototype machines 16
1.11 Prototype two-pole uniform-gapmachine 17
1.12 Elementary two-pole salientmachine 19
1.13 Multipolar machines 20
1.14 Main dimensions 21
1.15 Torque maintenance 24
1.16 Classification 25
2 Magnetic Circuits 26
2.1 Magnetic circuit properties 26
2.2 Magnetic materials 30
2.3 Magneticcircuitcalculation 32
2.4 Transformermagnetic circuits 32
2.5 Machine magnetic circuits 37
2.6 Total flux 43
2.7 Leakage fluxeffects in transformers 44
2.8 Leakage fluxeffects inmachines 50
2.9 Phase reactance 58
2.10 Unbalanced magnetic pull 59
2.11 Openmagnetic circuits 61
6
vl Contents
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-layerwindings 86
3.8 Double-layer windings 87
3.9 Fractional-slot windings 89
3.10 Types ofdouble-layerwinding 91
3.11 Choice ofwinding 92
3.12 E.M.F. ofwindings 94
3.13 Toothharmonics 103
3.14 Magnetomotive force ofwindings 107
4 Loss Dissipation 113
4.1 Dissipation ofheat 113
4.2 Ideal temperature-rise/time relation U3
4.3 Coolingofsmallunits
11
4.4 Coolingoflarge units 12fj
4.5 Heat transfer 128
4.6 Flowofcoolantin transformers 133
4.7 Limits oftemperature-rise 136
4.8 Thermal ratingoftransformers 138
4.9 Thermal ratingofmachines 140
5 Transformers: Theoryand Performance 142
5.1 Theory ofthe powertransformer 142
5.2 Power transformer onload 146
5.3 Losses andefficiency 147
5.4 Regulation 150
5.5 Operational equivalent circuits 152
5.6 Vibration andnoise 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-windingconnection 173
5.13 Zero-phase-sequence impedance 177
5.14 Tap-changing 179
5.15 Parallel operation 182
5.16 Coolingmethods 186
5.17 Protection 187
Vll
5.18 Testing 189
5.19 Special types 196
6 Transformers: Construction and Design 202
6.1 Constructional features 202
6.2 Cores 202
6.3 Tanks and oils 203
6.4 Windings andinsulation 205
6.5 Terminalsand fittings 207
6.6 Distribution transformers 207
6.7 Large transformers 211
6.8 Design 212
7 Polyphase Rotating Machines 215
7.1 Synchronousandinductionmachines 215
7.2 Rotational effects 217
7.3 Drive dynamics 220
7.4 Models 227
7.5 Dynamiccircuit theory 232
7.6 Industrial machines 244
7.7 Machines and power systems 248
8 Induction Machines: Theory and Performance 250
8.1 Development 250
8.2 Action oftheidealinductionmachine 250
8.3 Cage andslip-ringrotorwindings 257
8.4 Practicalinduction machine 259
8.5 Steady-state theory 264
8.6 Approximate theory 269
8.7 Current diagrams 272
8.8 Effects ofmachine parameters 276
8.9 Motorperformance in the steady state 278
8.10 Motorstarting 281
8.11 Harmoniceffects 290
8.12 High-torque cage motors 295
8.13 Motorspeedcontrol 303
8.14 Slip control 303
8.15 Pole-changing 311
8.16 Frequency control 316
8.17 Power-factor adjustment 322
8.18 Braking 324
8.19 Unbalanced operation 330
8.20 Induction generator 332
8.21 Transients 336
8.22 Testing 341
1
viii Contents
9 Induction Machines: Construction and Design 350
9.1 Constructional features 350
9.2 Main dimensions 353
9.3 Design 362
10 Synchronous Machines: Theory and Performance 366
10.1 Type andconstruction 366
10.2 Action ofthe ideal synchronous machine 367
10.3 Practical synchronousmachines 378
10.4 Steady-state theory 383
10.5 Steady-state performance 393
10.6 Transient performance 401
10.7 Short circuit 401
10.8 Stability 414
10.9 Excitation and voltage regulation 424
10.10 Generator control 433
10.1 Motorcontrol 440
10.12 Synchronous-induction motor 447
10.13 Synchronouscompensator 451
10.14 Surge voltages 453
10.15 Testing 455
11 Synchronous Machines: Constructionand Design 461
11.1 Types ofsynchronousmachine 461
11.2 Turbo-generators 461
11.3 Hydro-generators 469
11.4 Industrial generators 47\
11.5 Compensators 472
11.6 Motors 472
11.7 Main dimensions 472
11.8 Design 476
12 Special Machines 479
12.1 Forms ofspecialmachines 479
12.2 Voltage regulators 480
12.3 Inductorgenerators 484
12.4 Doubly-fedinduction motors 486
12.5 Polyphase reluctance motors 487
12.6 Permanent-magnet"machines 492
12.7 Powercontrolmachines 492
12.8 Servo controlmachines 493
12.9 Commutator machines 499
12.10 Polyphase commutatormotors 501
12.11 Single-phase motors 504
Contents ix
12.12 Single-phase commutatormotors 506
12.13 Single-phase induction motors 509
12.14 Linearmachines 514
References 526
ListofSymbols 533
Index 537

Preface
TheforerunnerofthisbookwasThePerformanceandDesignofA.C.Machines,
first publishedin 1936and subsequentlyrevised and reprinteda dozen times.
The combination ofdesign and performance provedgratifyingly acceptable,
and the book founditsway aroundthe English-readingworld.
But timeshavechanged. Design,revolutionizedby the digital computer,
has become the esotericpreoccupation ofthe few: performance interests
havewidened asa result ofthe advent ofthe bigmachine,the problem of
machine andpower-systeminteraction, the transient dynamics ofstartingand
braking,andthe influence on machine characteristics andcontrolmethods
ofpowerelectronics. That fewtextbookshave explored this theme is duein
part to the stronganalytical counter-attractions ofthe 'generalization'concept,
in whichmachine 'types'becomevariants ofacommon principle expressed
in terms ofelectric-circuit equations ofbehaviour. Powerful though themethod
is,circuit equationscan model amachine onlyin a restrictedway. Real
machineshave real magnetic,mechanical and thermal attributesas well, and
although theirbasic electromagnetic principlesare the same, the several types
do,in fact, differmarkedlyin performance.
The present textexpressesmybeliefthat machine performance can be
graspedmore readily throughappreciation offlux-current interaction than
by the manipulation ofmatrixequations;thelattergive meaningful quantita-
tive results onlyifthe physicalconcepts areunderstood. The treatmentthere-
fore begins withthe unifiedelectro-magnetic principles oftransformersand
machines, followedbymaterial common to both on magnetic circuits, wind-
ings andheat-dissipation. In dealingwithpractical transformers and three-
phaseinduction andsynchronous machines, the simple theory oftheideal
caseis followed progressivelyby departures from the ideal that affect the
practical performance inbothsteady and transient states. Designis discussed
ingeneral terms,andsome constructional detailsare illustrated. Machines
havingspecial features,andthose to whichnormal two-axismethods are not
so readily applied, are discussedin the final Chapter.
All formulae, whetherconcerned withelectrical, magnetic, mechanical or
thermalphenomena, are couched consistently in SI units. Onlyin numerical
examplesare decimalmultiples orsub-multiplesemployed forconvenience,
in conformity with IEC recommendations. Guidance in the use ofSI units,
xi