High Voltage Circuit Breakers, Design and Applications

473 Pages·2006·18.86 MB·English

by  Ruben D. Garzon

Design and Applications
Second Edition, Revised and Expanded
RUBEND . GARZON
Square D Co.
Smyrna, Tennessee
a%
MARCEL
MARCELD EKKEIRN,C .
DEKKER
Copyright © 2002 by Taylor & Francis
ISBN: 0-8247-0799-0
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Current printing (last digit):
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Copyright © 2002 by Taylor & Francis
To my grandson
E dB . Dommers
Copyright © 2002 by Taylor & Francis
The need for a second edition arises from the fact that, although it is generally
recognized that circuit breakers represent a relatively mature technology there are
some areas of thls technology where changes are inevitable and where some of
these changes take place continuously. The area of circuit breaker standards is one
in which substantial changes have taken place. These changes have been hven
primarily by the need and the desire to aclueve a high level of harmonization be-
tween the International (IEC) and the American (ANSI) Circuit Breaker Stan-
dards.
New standards have recently been published and revisions to some others
are in the process of being approved by both organizations. However, as new re-
quirements are being established for the new generations of equipment, it must be
recognized that a significant number of circuit breakers had been designed to meet
what are now obsolete standards. These circuit breakers are still in service and
consequently there is a need for preserving this type of information. It is the hope
that the readers will find this second edition to be usehl in providing a link be-
tween the old and the new requirements and furthermore that it can be considered
to be a valuable source of information and guidance for the application of the older
equipment.
Experience with the first edition has suggested the addition of some topics,
which would serve to strengthen the reader's knowledge, related to the practical
design and application of lugh voltage circuit breakers. More specifically, topics
dealing with dielectric design considerations are covered in a new chapter where
the basic concepts of dielectric strength field strength and types of insulation are
presented. The presentation of this material has maintained the original philosophy
of treating the subject based on a practical approach rather than a detailed mathe-
matical one.
Also added are sections dealing with the application of circuit breakers that
are connected to systems that have a large reactance to resistance (X/R) ratio and
applications where the circuit breaker is connected directly to power generators.
The application section on capacitance switching has been revised, ex-
panded, and updated to include recent work-related changes in the standards. The
coverage of switching series and shunt reactors and of temporary voltages has
Copyright © 2002 by Taylor & Francis
vi Preface to the Second Edition
been expanded in the switchmg overvoltages chapter, and a method for evaluating
the benefits of condition monitoring is included in the final chapter.
A number of other minor corrections and additions have been made
throughout the text in an attempt to provide the reader with an enhanced version of
this book.
Again I am grateful to all who encouraged me to work on the second edition
and who offered their comments and suggestions to make this possible.
Ruben D. Garzon
Copyright © 2002 by Taylor & Francis
PREFACE TO THE FIRST EDITION
Ever since the time when electrical energy was beginning to be utilized, a need
existed for a suitable switchng device that was able to initiate and to interrupt
the flow of the electric current. The early designs of such switching devices
were relatively crude and the principles of their operation relied only on empiri-
cal knowledge. Circuit breakers were developed on the basis of a "cut and try"
approach, but as the electrical system capacity continued to develop and grow, a
more scientific approach was needed to achieve optimized designs of circuit
breakers that would offer higher performance capabilities and greater reliability.
The transition of current interruption from being an empirical art to an ap-
plied science began in the 1920s. It was only then that worldwide research
started to unravel the subtleties of the electric arc and its significance to the cur-
rent interruption process. Since those early research days a great deal of litera-
ture on the subject of current interruption has been published. There is also a
significant number of technical articles on specific applications of circuit break-
ers that have been published, but most of these publications are highly theoreti-
cal. What is missing are publications geared specifically to the needs of the prac-
ticing engineer. There is a need for a simple source of reference that provides
simple answers to their most often-asked questions: Where does this come
from? What does it mean? What can I do with it? How can I use it? How can I
specify the right kind of equipment?
Circuit breakers are truly unique devices. They are a purely mechanical ap-
paratus connected to the electrical system, where they must systematically inter-
act with such a system providing a suitable path for the flow of the electric cur-
rent; furthermore, they must provide protection and control of the electric circuit
by either initiating or stopping the current flow. Combining these tasks into one
device requires a close interaction of two engineering disciplines and it suggests
that a good understanding of mechanical and electrical engineering principles is
paramount for the proper design and application of any circuit breaker.
It is the purpose of this book to bridge the gap between theory and practice,
and to do so without losing sight of the physics of the interruption phenomena.
This can be done by describing in a simple fashion the most common applica-
tion and design requirements and their solutions based on experience and pre-
sent established practices. The strictly mathematical approach will be avoided;
Copyright © 2002 by Taylor & Francis
viii Preface to the First Edition
however, the hndamentals of the processes will be detailed and explained from
a qualitative point of view.
Beginning with a simplified qualitative, rather than quantitative, description
of the electric arc and its behavior during the time when current is being inter-
rupted, we will then proceed to describe the response of the electric system and
the inevitable interaction of current and voltage during the critical initial rnicro-
seconds following the interruption of the current. We will show the specific be-
havior of different types of circuit breakers under different conditions.
Once the understanding of what a circuit breaker must do is gained we will
proceed to describe the most significant design parameters of such device. Par-
ticular emphasis will be placed in describing the contacts, their limitations in
terms of continuous current requirements and possible overload conditions, and
their behavior as the result of the electromagnetic forces that are present during
short circuit conditions and high imsh current periods. Typical operating
mechanisms will be described and the terminology and requirements for these
mechanisms will be presented.
Over the years performance standards have been developed not only in the
U.S. but in other parts of the world. Today, with the world tending to become a
single market, it is necessary to understand the basic differences between these
standards. Such an understanding will benefit anyone who is involved in the
evaluation of circuit breakers designed and tested according to those different
standards.
The two most widely and commonly recognized standard documents today
are the ones issued by the American National Standards Institute (ANSI) and by
the International Electrotechnical Commission (IEC). The standards set forth by
these two organizations will be examined, their differences will be explained
and by realizing that the principles upon which they are based are mainly local-
ized operating practices, it is hoped that the meaning of each of the required
capabilities will be thoroughly understood. This understanding will give more
flexibility to the application engineer for making the proper choices of equip-
ment for any specific application and to the design engineer for selecting the
appropriate parameters upon which to base the design of a circuit breaker that
can be considered to be a world class design because it meets the requirements
of all of the most significant applicable standards.
This type of book is long overdue. For those of us who are involved in the
design of these devices it has been a long road of learning. Many times not hav-
ing a concise, readily available collection of design tips and general design in-
formation, we learned most of the subtleties of these designs by experience. For
those whose concern is the application and selection of the devices there is a
need for some guidance that is independent of commercial interests. As was said
before, there have been a number of publications on the subject, but most, if not
all of them, devote the treatment of the subject to the strict mathematical deriva-
tion of formulae with a textbook approach. The material presented here is lim-
Copyright © 2002 by Taylor & Francis
Preface to the First Edition ix
ited to what is believed to be the bare essentials, the hdamentals of the funda-
mentals, the basic answers to the most common questions on the subject.
The book titled Circuit Interruption Theory and Techniques edited by Tho-
mas Browne, Jr., and published by Marcel Dekker Inc., in 1984 partially meets
the aims of the new publication. A more recent book, Vacuum Switchgear, writ-
ten by Allan Greenwood and published by The Institution of Electrical Engi-
neers, London, 1994, as its title implies, is limited and covers only a particular
interrupting medium, vacuum. Earlier works have now become obsolete since
some of the new design concepts of interrupter designs and revisions to the gov-
erning standards were not thoroughly covered. But none of these previous publi-
cations covers specific design details, applications, interpretation of standards,
and equipment selection and specification.
There are a great number of practicing electrical engineers in the electrical
industry, whether in manufacturing, industrial plants, construction or public
utilities, who will welcome this book as an invaluable tool to be used in their
day-to-day activities.
The references at the end of each chapter are intended to provide the readers
with a source of additional information on the subject. These lists are by no
means exhaustive, but they were selected as being the most representative in
relation to the subject at hand.
The most important contributors to this book are those pioneer researchers
who laid the foundations for the development of the circuit breaker technology. I
am specially indebted to Lome McConnell from whom I learned the trade and
who encouraged me in my early years. I am also indebted to all those who ac-
tively helped me with their timely comments and especially to the Square D
Company for their support on this project. Most of all, I am especially grateful
to my wife Maggi for her support and patience during the preparation of this
book.
Ruben D. Ganon
Copyright © 2002 by Taylor & Francis
Preface to the Second Edition V
Preface to the First Edition vii
1 Electric Arc Fundamentals
1.0 Introduction
1.1 Basic Theory of Electrical Discharges
1.1.1 Non-Self-sustaining Discharges
1.1.2 Self-Sustaining Discharges
1.2 The Electric Arc
1.2.1 High-Pressure Arcs
1.2.2 Low-Pressure (Vacuum) Arcs
1.3 The Alternating Current Arc
1.4 The Current Interruption Process
1.4.1 Interruption of Direct Current
1.4.2 Interruption of Alternating Currents
1.5 Review of Main Theories of AC Intemption
1.5.1 Slepian's Theory
1.5.2 Prince's Theory
1.5.3 Cassie's Theory
1.5.4 Mayr's Theory
1.5.5 Browne's Combined Theory
1S .6 Modern Theories
References
2 Short Circuit Currents
2.0 Introduction
2.1 Characteristics of the Short Circuit Current
2.1.1 Transient Direct Current Component
2.1.2 The Volt-Time Area Concept
2.1.3 Transient Alternating Current Components
2.1.4 Asymmetry of Three-Phase Short Circuit Currents
2.1.5 Measuring Asymmetrical Currents
2.2 Calculation of Short Circuit Currents
Copyright © 2002 by Taylor & Francis
xii Contents
2.2.1 The Per Unit Method
2.2.2 The MVA Method
2.3 Unbalanced Faults
2.3.1 Introduction to Symmetrical Components
2.4 Forces Produced by the Short Circuit Currents
2.4.1 Direction of the Forces Between Current Carrying Conductors
2.4.2 Calculation of Electrodynamic Forces Between Conductors
2.4.3 Forces on Conductors Produced by Three-Phase Currents
References
3 Transient Recovery Voltage
3.0 Introduction
3.1 Transient Recovery Voltage: General Concepts
3.1.1 Basic Assumptions for TRV Calculations
3.1.2 Current Injection Techmque
3.1.3 Traveling Waves and the Lattice Diagram
3.2 Calculation of Transient Recovery Voltages
3.2.1 Single Frequency Recovery Voltage
3.2.2 Double Frequency Recovery Voltage: General Case
3.2.3 Particular Case of Double Frequency Recovery Voltage
3.2.4 Short-Line Fault Recovery Voltage
3.2.5 Initial Transient Recovery Voltage
References
4 Switching Overvoltages
4.0 Introduction
4.1 Contacts Closing
4.1.1 Closing of a Line
4.1.2 Reclosing of a Line
4.1.3 Energizing Unloaded Transformers
4.2 Contact Opening
4.2.1 Interruption of Small Capacitive Currents
4.2.2 Interruption of Inductive Load Currents
4.2.3 Current Chopping
4.2.4 Virtual Current Chopping
4.2.5 Temporary Overvoltages
4.2.6 Controlling Overvoltages
References
5 Types of Circuit Breakers
5.0 Introduction
5.1 Circuit Breaker Classifications
5.1.1 Circuit Breaker Types by Voltage Class
5.1.2 Circuit Breaker Types by Installations
Copyright © 2002 by Taylor & Francis