Table Of ContentIET Power Series 18
Vacuum Switchgear V Vacuum
a
c
u
u
m
Switchgear
This book provides a broad perspective of vacuum switchgear Dr Greenwood is presently Philip Sporn S
drawn from the author’s many years of experience in this field. Professor of Engineering at Rensselaer, the
Allan Greenwood describes the development of the technology oldest engineering school in North America. His w
from the earliest beginnings to the most recent designs now on professional career, which started with a B.T.-H.
apprenticeship in 1940, has been spent about i
offer by leading companies around the world. t
equally in industry and university environments. c
The book starts with a solid foundation in the physics of the His particular interests are in power switching
h
vacuum arc, in vacuum breakdown and in the fundamentals equipment and the interactions of such
of current interruptions in vacuum. For the user there is an equipment with power systems. He was one g
exhaustive chapter on applications, which spans all devices of the small team that developed the first high e
power vacuum interrupters for the General
from contactors through switches and reclosers to power circuit Electric Co. (USA) in the 1950s and has been a
breakers. Maintenance is also addressed. There are four chapters
involved with this technology ever since. He r
on different aspects of design and another on testing, which holds many patents and has published widely
should appeal to the designer. The chapter on manufacturing on this subject. He is the author of Electrical
concentrates on the interrupter as its manufacture is so entirely transients in power systems (John Wiley &
different from that required for oil and gas-blast circuit breakers. Sons, 2nd edn, 1991). Allan Greenwood
The treatment is comprehensive so the book will be useful to Dr Greenwood is a life Fellow of the IEEE,
users, designers and manufacturers alike, and to students who an Attwood Associate of CIGRE and a former
wish to become acquainted with the subject. Visiting Fellow of Churchill College, Cambridge.
G
r
e
e
n
w
The Institution of Engineering and Technology o
o
www.theiet.org d
0 85296 855 8
978-0-85296-855-0
IET POWER SERIES 18
Series Editors: Prof. A.T. Johns
J.R. Platts
Dr D. Aubrey
Vacuum
Switchgear
Other volumes in this series:
Volume 1 Power circuit breaker theory and design C.H. Flurscheim (Editor)
Volume 4 Industrial microwave heating A.C. Metaxas and RJ. Meredith
Volume 7 Insulators for high voltages J.S.T. Looms
Volume 8 Variable frequency AC motor drive systems D. Finney
Volume 10 SF6 switchgear H.M. Ryan and G.R. Jones
Volume 11 Conduction and induction heating EJ. Davies
Volume 13 Statistical techniques for high voltage engineering W. Hauschild and
W. Mosch
Volume 14 Uninterruptable power supplies J. Platts and J.D. St Aubyn (Editors)
Volume 15 Digital protection for power systems A.T. Johns and S.K. Salman
Volume 16 Electricity economics and planning T.W. Berrie
Volume 18 Vacuum switchgear A. Greenwood
Volume 19 Electrical safety: a guide to causes and prevention of hazards
J. Maxwell Adams
Volume 21 Electricity distribution network design, 2nd edition E. Lakervi and
EJ. Holmes
Volume 22 Artificial intelligence techniques In power systems K. Warwick, A.O. Ekwue
and R. Aggarwal (Editors)
Volume 24 Power system commissioning and maintenance practice K. Harker
Volume 25 Engineers' handbook of industrial microwave heating RJ. Meredith
Volume 26 Small electric motors H. Moczala et al.
Volume 27 AC-DC power system analysis J. Arrill and B.C. Smith
Volume 29 High voltage direct current transmission, 2nd edition J. Arrillaga
Volume 30 Flexible AC Transmission Systems (FACTS) Y-H. Song (Editor)
Volume 31 Embedded generation N. Jenkins et al.
Volume 32 High voltage engineering and testing, 2nd edition H.M. Ryan (Editor)
Volume 33 Overvoltage protection of low-voltage systems, revised edition P. Hasse
Volume 34 The lightning flash V. Cooray
Volume 35 Control techniques drives and controls handbook W. Drury (Editor)
Volume 36 Voltage quality in electrical power systems J. Schlabbach et al.
Volume 37 Electrical steels for rotating machines P. Beckley
Volume 38 The electric car: development and future of battery, hybrid and fuel-cell
cars M. Westbrook
Volume 39 Power systems electromagnetic transients simulation J. Arrillaga and
N. Watson
Volume 40 Advances in high voltage engineering M. Haddad and D. Warne
Volume 41 Electrical operation of electrostatic precipitators K. Parker
Volume 43 Thermal power plant simulation and control D. Flynn
Volume 44 Economic evaluation of projects in the electricity supply industry H. Khatib
Volume 45 Propulsion systems for hybrid vehicles J. Miller
Volume 46 Distribution switchgear S. Stewart
Volume 47 Protection of electricity distribution networks, 2nd edition J. Gers and
E. Holmes
Volume 48 Wood pole overhead lines B. Wareing
Volume 49 Electric fuses, 3rd edition A. Wright and G. Newbery
Volume 51 Short circuit currents J. Schlabbach
Volume 52 Nuclear power J. Wood
Volume 905 Power system protection, 4 volumes
Vacuum
Switchgear
Allan Greenwood
The Institution of Engineering and Technology
Published by The Institution of Engineering and Technology, London, United Kingdom
First edition © 1994 The Institution of Electrical Engineers
Reprint with new cover © 2007 The Institution of Engineering and Technology
First published 1994
Reprinted 2007
This publication is copyright under the Berne Convention and the Universal Copyright
Convention. All rights reserved. Apart from any fair dealing for the purposes of research
or private study, or criticism or review, as permitted under the Copyright, Designs and
Patents Act, 1988, this publication may be reproduced, stored or transmitted, in any
form or by any means, only with the prior permission in writing of the publishers, or in
the case of reprographic reproduction in accordance with the terms of licences issued
by the Copyright Licensing Agency. Inquiries concerning reproduction outside those
terms should be sent to the publishers at the undermentioned address:
The Institution of Engineering and Technology
Michael Faraday House
Six Hills Way, Stevenage
Herts, SCI 2AY, United Kingdom
www.theiet.org
While the author and the publishers believe that the information and guidance given
in this work are correct, all parties must rely upon their own skill and judgement when
making use of them. Neither the author nor the publishers assume any liability to
anyone for any loss or damage caused by any error or omission in the work, whether
such error or omission is the result of negligence or any other cause. Any and all such
liability is disclaimed.
The moral rights of the author to be identified as author of this work have been
asserted by him in accordance with the Copyright, Designs and Patents Act 1988.
British Library Cataloguing in Publication Data
A catalogue record for this product is available from the British Library
ISBN (10 digit) 0 85296 855 8
ISBN (13 digit) 978-0-85296-855-0
Printed in the UK by Short Run Press Ltd, Exeter
Reprinted in the UK by Lightning Source UK Ltd, Milton Keynes
Contents
Page
Acknowledgments x
Preface xi
1 Historical review—how we arrived at where we are today 1
.1 Introduction 1
.2 Early pioneers 2
.3 Industrial follow-up and the doldrum years 4
.4 Emergence of the commercial vacuum switch 5
.5 The first vacuum power circuit breakers 9
.6 The British connection 15
.7 Penetrating a conservative market 18
.8 The Japanese story 21
.9 Concluding comments 21
.10 References 23
The vacuum arc 25
2.1 Definition 25
2.2 Appearance of a vacuum arc 25
2.3 Arc voltage 29
2.4 The vacuum arc in a magnetic field 30
2.5 Positive ions in the vacuum arc 32
2.6 Model for the vacuum arc 32
2.6.1 Introduction 32
2.6.2 Model for the cathode spot 34
2.6.3 Model for the arc column and the anode 41
2.7 References 47
Vacuum breakdown 49
3.1 Implications for vacuum switchgear 49
3.2 Basic notions about breakdown in gas
and breakdown in vacuum 50
3.3 Electrode effects 55
3.4 References 58
Current interruption in vacuum 60
4.1 Description of the task 60
vi Contents
4.2 Interrupting a diffuse vacuum arc 62
4.2.1 The declining current 62
4.2.2 Current zero and the immediate post-arc period 65
4.2.3 Post-arc current 74
4.3 Interrupting a constricted vacuum arc 76
4.4 Keeping the arc diffuse 77
4.4.1 General observations 77
4.4.2 Increasing the internal surface area of the switch 78
4.4.3 Use of an axial magnetic field 79
4.5 Current chopping 81
4.5.1 The phenomenon and the implications for power systems 81
4.5.2 Fundamentals of the chopping phenomenon 84
4.5.3 Statistical approach to vacuum arc instability 86
4.6 High frequency current interruption 89
4.6.1 Significance in the power switching context 89
4.6.2 Physical phenomena associated with high frequency
current interruption 91
4.7 Interruption of direct current 96
4.8 Vacuum interrupters in series 98
4.9 References 104
5 Design of vacuum switchgear 1: the vacuum interrupter 108
5.1 Preamble 108
5.2 Fundamental requirements for the interrupter 108
5.3 Contacts 109
5.3.1 Material: a shopping list of ideal requirements 109
5.3.2 Solutions to the contact material problem 110
5.3.4 Contact geometry 114
5.4 Bellows 121
5.5 Shields 124
5.6 Vacuum enclosure 126
5.7 Overall interrupter design 128
5.7.1 Electrical considerations 128
5.7.2 Mechanical considerations 129
5.7.3 Thermal considerations 131
5.8 References 134
6 Design of vacuum switchgear 2: the operating mechanism
and other mechanical features 136
6.1 Introduction 136
6.2 Contact popping 137
6.2.1 Origin of popping forces 137
6.2.2 Magnitude of the popping force and implications for
mechanism design 141
6.2.3 Providing the contact holding force 143
6.3 Contact bounce and rebound 146
6.3.1 Contact dynamics 146
6.3.2 Controlling contact bounce 147
6.4 Contact welding 150
Contents vii
6.5 Spring-activated, cam-follower mechanism 152
6.5.1 Basics 152
6.5.2 Spring-activated mechanism for three-pole
circuit breaker 154
6.5.2.1 Closing spring charging 156
6.5.2.2 Closing operation 156
6.5.2.3 Opening operation 157
6.5.2.4 Trip-free operation 157
6.6 Four-bar linkage 159
6.7 Solenoid operated mechanisms 162
6.7.1 Mechanisms for contactors 162
6.7.2 Mechanisms for switches 165
6.7.3 Solenoid design 168
6.8 Mechanism for series operation of interrupters 173
6.9 References 173
7 Design of vacuum switchgear 3: design for versatility 174
7.1 Basic notions 174
7.2 Designing vacuum switchgear for a range of ratings 174
7.2.1 Adapting to higher voltages 174
7.2.2 Adapting to higher load current 178
7.2.3 Adapting to higher short-circuit current 178
7.3 Single pole breakers 179
7.4 The OEM market 180
8 Design of vacuum switchgear 4: packaging 181
8.1 Introduction 181
8.2 Air-insulated equipment 182
8.2.1 Traditional metal-clad gear 182
8.2.2 Multiple stacking of circuit breakers 182
8.2.3 Air-insulated distribution switchgear 184
8.3 Foam-insulated switchgear 186
8.4 Gas-insulated equipment 189
8.4.1 Vacuum switchgear for gas-insulated substations 189
8.4.2 Gas-insulated distribution switchgear using vacuum 189
8.5 Vacuum switchgear with composite solid/gas insulation systems 191
8.6 Oil-insulated vacuum switchgear 194
8.7 Conversion kits 194
8.8 Hybrid circuit breakers 196
8.9 References 196
9 Manufacture of vacuum switchgear 197
9.1 Organisation and general remarks 197
9.2 The vacuum interrupter 197
9.2.1 Contacts 197
9.2.2 Preparation of internal parts 199
9.2.3 Subassemblies 200
9.2.4 Final assembly 202
viii Contents
9.2.5 Testing 203
9.2.6 Facilities 205
9.3 Breaker assembly 206
9.3.1 Breakers for metal-clad equipment 206
9.4 Reference 206
10 Application of vacuum switchgear 207
10.1 Introduction 207
10.2 Comments on standards 207
10.3 Basic duties and basic concerns 209
10.4 Load switching 210
10.5 Interrupting fault currents 211
10.5.1 Selecting a short-circuit current rating 211
10.5.2 The evolving fault 212
10.5.3 Voltage considerations 212
10.6 Interrupting small inductive currents 216
10.6.1 Concerns 216
10.6.2 Current chopping 216
10.6.3 Reignitions when switching unloaded transformers
and reactors 218
10.7 Capacitance switching 219
10.7.1 Energising a capacitor bank 219
10.7.2 Bank-to-bank capacitor switching 222
10.7.3 Disconnecting a capacitor bank 225
10.7.4 Switching cables 227
10.7.5 Line dropping 230
10.8 Recloser applications 231
10.9 Generator breakers 231
10.10 Arc furnace switching 232
10.11 Motor switching 233
10.11.1 Introduction 233
10.11.2 Energising a motor 233
10.11.3 Disconnecting a running motor 234
10.11.4 Aborting a motor start 235
10.11.5 Recommendation 235
10.12 On-load tap changing 235
10.13 Unusual applications 235
10.13.1 HVDC circuit breakers 235
10.13.2 Parallel operation of vacuum interrupters 236
10.13.3 Application in fusion machines 239
10.13.4 Switching operations at nonstandard frequencies 241
10.14 Triggered vacuum gaps 242
10.15 Vacuum fuses 246
10.16 References 248
11 Testing vacuum switchgear 251
11.1 Introduction 251
11.2 Testing for vacuum 251
Contents ix
11.3 Non-sustained disruptive discharge 252
11.4 Testing for contact condition after undergoing short-circuit 254
11.5 Determining switch life 254
11.6 Testing for X-rays 255
11.7 Comparative testing of vacuum switchgear products 256
11.7.1 Problems of testing 256
11.7.2 Test method 256
11.7.3 The Weibull distribution 257
11.7.4 Test programme 262
11.7.5 Discussion of results 262
11.8 References 266
12 Maintenance of vacuum switchgear 267
12.1 General comments 267
12.2 Safety 267
12.3 Electrical maintenance 267
12.3.1 Interrupters 267
12.3.2 Insulation checks 268
12.3.3 Primary circuit resistance check 269
12.4 Mechanical maintenance 269
12.4.1 Visual inspection 269
12.4.2 Wipe and gap adjustments 269
12.4.3 Timing 271
12.4.4 Lubrication 272
12.5 Maintenance of the cubicle and auxiliaries 272
Description:This book provides a broad perspective of vacuum switchgear drawn from the author's many years of experience in this field. Allan Greenwood describes the development of the technology from the earliest beginnings to the most recent designs now on offer by leading companies around the world. The book
