Table Of ContentPOWER ENGINEERISNG SERIES 10F
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switchgear
H M Ryan & G R Jones
Peter Peregrinus Ltd. on behalf of the Institution of Electrical Engineers
IEE POWER SERIES 10
Series Editors: Professor A. T. Johns
J. R. Platts
Dr. D. Aubrey
switchgear
Other volumes in this series
Volume 1 Power circuit breaker theory and design
C. H. Flurscheim (Editor)
Volume 2 Electric fuses
A. Wright and P. G. Newbery
Volume 3 Z-transform electromagnetic transient analysis in
high-voltage networks
W. Derek Humpage
Volume 4 Industrial microwave heating
A. C. Metaxas and R. J. Meredith
Volume 5 Power system economics
T. W. Berrie
Volume 6 High voltage direct current transmission
J. Arrillaga
Volume 7 Insulators for high voltages
J. S. T. Looms
Volume 8 Variable frequency AC motor drive systems
D. Finney
Volume 9 Electricity distribution network design
E. Lakervi and E. J. Holmes
6
switchgear
H M Ryan & GR Jones
Peter Peregrinus Ltd. on behalf of the Institution of Electrical Engineers
Published by: Peter Peregrinus Ltd., London, United Kingdom
© 1989: Peter Peregrinus Ltd.
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 or otherwise—without the prior written
permission of the publisher.
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
judgment 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.
British Library Cataloguing in Publication Data
Ryan, KM.
SF switchgear
6
1. Electrical equipment. Switchgear & controlgear—
Manuals
I. Title. II. Jones, G.R. (Gordon Rees) 1938-
III. Series
621.317
ISBN 0 86341 1231
Printed in England by Biddies Ltd., Guildford
Contents
Page
1 Introduction 1
2 Fundamental properties of SF 6
6
3 Types of SF Interrupters 15
6
4 Characteristics of SF Interrupters 22
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4.1 Pressure characteristics 22
4.2 Thermal characteristics 31
4.2.1 Gas heating 31
4.2.2 Nozzle ablation 33
4.3 Electromagnetic characteristics 37
4.4 Thermal-recovery characteristics 43
4.4.1 Axisymmetric (puffer-type) interrupters 43
4.4.1.1 Nozzle and contact considerations 44
4.4.1.2 Piston-travel and contact-throttling
effects 50
4.4.1.3 SF Mixtures 51
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4.4.1.4 Liquid SF injection 53
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4.4.2 Asymmetric (rotary arc) interrupters 53
4.5 Dielectric recovery 54
4.5.1 Dielectric recovery of the remnant arc column 55
4.5.2 Scaling of the dielectric recovery of the arc column 58
4.5.3 Retarded dielectric recovery 60
4.5.4 Dielectric-recovery requirements for medium-
voltage interrupters 61
4.5.5 Gases with higher dielectric strength 62
5 Arc modelling and computer-aided methods for interrupter-design
evaluation 63
5.1 Field calculations 64
5.2 Arc modelling 69
5.3 Puffer modelling . 72
5.4 Rotary-arc interrupter modelling 73
vi Contents
Impactof SF technology upon transmission switchgear 76
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6.1 Commercial considerations 80
6.2 Circuit-breaker assemblies 82
6.3 Metalclad installations 84
6.3.1 Components and structure 88
6.3.2 Insulation co-ordination 95
6.3.3 Internal arcing faults in metalclad enclosures 100
6.3.4 Internal maintenance requirements and reliability 103
6.4 Artificial current zeros 103
6.4.1 Generator circuit breakers 104
6.4.2 High-voltage DC circuit breakers 107
6.5 Particular examples of SF -insulated installations 113
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Impact of SF technology upon distribution and utility switchgear 116
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7.1 Operation and system requirements 116
7.2 Relative merits of SF , vacuum and more traditional circuit
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breakers 118
7.3 Puffer circuit breakers 121
7.4 Rotary-arc circuit breakers 122
7.5 SF self-extinguishing circuit breakers 124
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7.6 Insulation of distribution switchgear 126
7.7 Fuse-switch combinations 127
7.8 Disconnecting and earthing switches 132
Operating mechanisms for SF circuit breakers 134
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8.1 Energy requirements 134
8.2 Reliability 136
8.3 Puffer circuit-breaker mechanisms 136
8.4 Choice of drive type for puffer interrupters 139
8.5 Modelling puffer-drive mechanisms 140
Impact of SF technology upon regulations, testing and instrumentation 143
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9.1 Circuit-breaker testing 143
9.1.1 Electrical tests 143
9.1.1.1 Test circuits 144
9.1.1.2 Recent modifications to the basic Weil
Circuit 147
9.1.1.3 Test methods for three phases in the tank
breaker 149
9.1.1.4 Unit testing of multibreak tank-type
circuit breakers 151
9.1.1.5 Synthetic tests for closing and auto-
reclosing duties 154
9.1.1.6 Short-circuit tests for disconnecting
switches 156
9.1.1.7 Synthetic tests for high-voltage DC cir-
cuit breakers 158
9.1.2 • Mechanical tests 160
9.1.3 Chemical tests 162
9.1.4 Particular performance capabilities of SF circuit
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breakers 165
Contents vii
9.2 Instrumentation and diagnostics 167
9.2.1 Electrical measurements 167
9.2.2 Mechanical-drive measurements 170
9.2.3 Aerodynamic measurements 172
9.2.4 Radiation measurements 173
9.2.5 Chemical measurements 176
10 Conclusions 178
11 References 180
Index 192
Acknowledgments
The authors wish to acknowledge the assistance provided by their many col-
leagues and acquaintances worldwide. Their willingness and prompt responses
contributed to the acquisition of updated information. The unstinting effort of
Miss E. Kevan with the typescript is also greatly appreciated.
Acknowledgment is made to the following organisations for the use of
illustrations: Brown Boveri Co. Ltd.; Brush Switchgear Ltd.; GE Co. USA;
GEC High Voltage Switchgear Ltd.; A/S Norsk Elektrisk; Bonneville Power
Administration, Oregon, USA; ASEA High Voltage Switchgear; Siemens AG;
Mitsubishi Electric Corporation; NEI Reyrolle Ltd.; Hitachi Ltd.; Toshiba
Corporation; South Wales Switchgear Ltd.; Merlin-Gerin; McGraw-Edison
Co.; Kansai Electric Power Co. Inc.; Sprecher Energy; Tokyo Electric Power
Co. Inc.; Ontario Hydro; Westinghouse R&D Center; Electric Power Develop-
ment Co. Ltd.; Yaskawa Electric Manufacturing Co. Ltd.; Yorkshire Switch-
gear Group; Square D Co.; KEMA High Power Laboratories; Fuji Electric
Corporation R&D Ltd.; CESI; Oak Ridge Nuclear Laboratories, USA.
Chapter 1
Introduction
The purpose of a circuit breaker is to ensure the unimpeded flow of current in
a network under normal operating conditions, and to interrupt the flow of
excessive current in a faulty network. It may also be required to interrupt load
current under some circumstances and to perform an open-close-open sequence
(auto-reclosing) on a fault in others. The successful achievement of these duties
relies upon the availability of good mechanical design to meet the demands of
opening and closing the circuit-breaker contacts, and good electrical design to
ensure that the circuit breaker can satisfy the electrical stresses.
During the opening and closing sequences an electric arc occurs between the
contacts of the circuit breaker, and advantage is taken of this discharge to assist
in the circuit-interruption process. For instance, in an AC network, the arc is
tolerated in a controlled manner until a natural current zero of the waveform
occurs when the discharge is rapidly quenched to limit the reaction of the system
to the interruption. With asymmetric waveforms and for DC interruption,
advantage is taken of the arc resistance for damping purposes or to generate a
controlled circuit instability to produce an artificial current zero. The arc
control demanded by such procedures may require gas pressurisation and flow,
which in turn make additional demands upon the operating mechanism.
Although this description is simplified it serves to illustrate the complexity of
the interactions involved in circuit interruption. These interactions are deter-
mined on the one hand by the nature of the arcing and arc quenching medium,
and on the other by the network demands. Since Garrard's review (1976),
increasing use has been made of SF as the arc-quenching medium, initially
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perhaps because of its outstanding electrical-insulation properties and its chemi-
cal inertness under normal conditions. However, with increased usage there was
a growing awareness that SF also possessed attractive arc quenching properties
6
in its own right. Subsequently, there was a realisation that it also possessed
compressive and thermal absorption properties, which are sufficiently different
from those of other interrupter media such as oil and air, so that different modes
of utilisation in an interrupter environment could be used to advantage. These
have led to the evolution of puffer, suction, self-pressurising and rotary-arc
