Table Of ContentHigh Voltage
eire i rea ers
Design and Applications
Ruben D. Garzon
High Voltage
Circuit Breakers
Design and Applications
Ruben D. Garzon
Square 0 Co., Smyrna,Tennessee
Marcel Dekker, Inc. NewYorkeBaseleHong Kong
LibraryofCongressCataloging-in-PublicationData
Garzon,R D. (RubenD.)
Highvoltagecircuitbreakers: designandapplications/Ruben Garzon.
p. cm. - (Electricalengineeringandelectronics: v. 100)
Includesindex.
ISBN0-8247-982I-X(hardcover: alk. paper)
1. Electriccircuit-breakers. 2. Electricpowerdistribution
-Hightension-Equipmentandsupplies. I. Title. II. Series.
TK2842.G27 1996
621.3l'7-dc2l
96-37206
CIF
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Copyright ©1997byMARCELDEKKER, INC. All RightsReserved.
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PREFACE
Eversincethe time when electrical energywas beginningto be utilized, there
has beena need for suitable switching devices capable ofinitiating and inter
rupting the flow ofthe electric current. The early designs of such switching
devices were relatively crude and the principles oftheir operation relied only
on empirical knowledge. Circuit breakers were developed on the basis of.a
"eut and try" approach, but as the electrical system capacity continued to de
velop and grow, a more scientific approach was needed to achieve optimized
designs of circuit breakers that would offer higher performance capabilities
andgreaterreliability.
The transition of current interruption from being an empirical art to an
applied sciencebeganinthe 1920's. Itwas onlythenthat worldwide research
started to unravel the subtleties ofthe electric arc and its significance on the
current interruptionprocess. Sincethose early research days, therehasbeena
great deal ofliterature on the subject ofcurrent interruption. There have also
been numerous technical articles on specific applications of circuit breakers,
but most ofthesepublications are highly theoretical. What has beenmissing
arepublications geared specifically to the needs ofthepracticing engineer-a
simple source of reference that provides simple answers to the most often
askedquestions: Wheredoesthis comefrom? Whatdoesitmean? What canI
do withit? How canIuseit? HowcanIspecifytherightkindofequipment?
Circuit breakers are truly unique devices. They are a purely mechanical
apparatus connectedto the electrical system. They must systematically inter
act with the system, providing a suitablepathfor the flow ofthe electric cur
rent; furthermore, they mustprovideprotection and control ofthe electric cir
cuit by either initiating or stopping the current flow. Combining these tasks
into one device requires a closeinteraction oftwo engineering disciplines. A
good understanding of mechanical and electrical engmeering principles is
paramountfortheproperdesignandapplicationofany circuitbreaker.
Thepurpose ofthisbookis to bridgethe gap between theory and practice,
andto do so withoutlosingsightofthephysicsofthe interruptionphenomena.
Theapproach is to describethe most common application and design require
ments and their solutions based on experience and present established prac
tices. Astrictlymathematicalapproachisavoided; however, thefundamentals
oftheprocessesaredetailedand explainedfromaqualitativepointofview.
v
vi Preface
Beginning with a simplified qualitative, rather than quantitative, descrip
tion ofthe electric arc and its behaviorduring the time when current is being
interrupted, we will thenproceed to describe the response ofthe electric sys
temandtheinevitableinteractionofcurrentandvoltageduringthe criticalini
tial microsecondsfollowingthe interruption ofthe current. We will show the
specific behavior of different types of circuit breakers under different condi
tions.
After explaining what a circuit breaker must do, we will proceed to de
scribe the most significant design parameters of such device. Particular em
phasis 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 inrush current periods. Typical operating
mechanisms willbedescribedand the terminology and requirements for these
mechanismswillbepresented.
Overthe yearsperformance standardshave been developednot only in the
UnitedStatesbutinotherparts oftheworld. Today, withtheworldtendingto
become a single market, it is necessary to understand the basic differences
among these standards. Suchanunderstanding will benefit anyone who is in
volved in the evaluation of circuit breakers designed and tested according to
thesedifferentstandards.
Thetwo mostwidelyand commonlyrecognizedstandardsdocuments today
are issuedbythe AmericanNational Standards Institute (ANSI) and the Inter
national Eleetrotechnical Commission (lEC). The standards set fort by these
two organizations will be examined and their differences will be explained.
Byrealizingthattheprinciplesuponwhichthey arebasedare mainlylocalized
operatingpractices, itis hoped that the meaning ofeach ofthe required capa
bilities will be thoroughly understood. This understanding will give more
flexibility to the application engineer for choosing the proper equipment for
anyspecificapplicationandto thedesignengineerforselectingtheappropriate
parameters upon which to base the design of a circuit breaker, which must
meettherequirements ofallofthe mostsignificantapplicable standardsifitis
tobeconsideredofworld-class.
Thistype ofbookislongoverdue. Forthose ofus who are involved inthe
design ofthese devices, it has been a longroad oflearning. Many times, not
havinga concise sourceofreadily available collectionofdesigntips and gen
eraldesigninformation, wehavehadto learnthe subtletiesofthese designsby
experience. Forthose whose concern is the application and selection ofthe
devices, there is a need for some guidance that is independent ofcommercial
interests. Therehavebeena number ofpublications onthe subject, but most,
ifnot all of them, use a textbook approach to treat the subject with a strict
mathematicalderivationofformulae. Thematerialpresentedhere islimitedto
Preface vii
what is believed to be the bare essentials, the fundamentals ofthe fundamen
tals, andthebasicanswerstothemostcommonquestionsonthesubject.
Thebook Circuit Interruption: Theory and Techniques, edited by Thomas
Browne, Jr. (Marcel Dekker, 1984)partially meets the aims ofthenewpubli
cation, but earlierworks havebecome obsolete since some ofthe new design
concepts ofinterrupter designs and revisions to the governing standards were
not thoroughly covered. None ofthese previous publications covers specific
designdetails, application,interpretationofstandards, and equipmentselection
andspecification.
Therearea great numberofpracticing electrical engineersinthe electrical
industry, whether in manufacturing, industrial plants, construction, or public
utilities, who will welcome this book as an invaluable tool to be used intheir
day-to-dayactivities.
The mostimportant contributors to this book are those pioneerresearchers
who laidthefoundations forthedevelopmentofthe circuitbreakertechnology.
Iamspecially indebted to Lome McConnell, from whomI learnthetradeand
who encouragedmeinmy earlyyears. Iamalso indebtedto allthose who ac
tivelyhelpedmewiththeirtimely comments, and especiallyto the Square"D"
Co. for its supportonthisproject. Mostofall, I am especially grateful to my
wife, Maggi,forhersupportandpatienceduringthepreparationofthisbook.
RubenD. Garzon
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CONTENTS
Preface v
1. TheFundamentalsofElectricArcs 1
1.0 Introduction 1
1.1 BasicTheoryofElectricalDischarges 2
1.1.1 Non-Self-SustainingDischarges 2
1.1.2 Self-SustainingDischarges 4
1.2 TheElectricArc 5
1.2.1 HighPressureArcs 5
1.2.2 LowPressure(Vacuum) Arcs 8
1.3 TheAlternatingCurrentArc 10
1.4 TheCurrentInterruptionProcess 11
1.4.1 Interruptionof DirectCurrent 11
1.4.2InterruptionofAlternatingCurrent 14
1.5ReviewofMainTheoriesofacInterruption 19
1.5.1 Slepian'sTheory 20
1.5.2 Prince'sTheory 21
1.5.3 Cassie'sTheory 22
1.5.4 Mayr'sTheory 23
1.5.5 Browne'sCombinedTheory 24
1.5.6 ModernTheories 25
References 26
2. ShortCircuitCurrents 29
2.0 Introduction 29
2.1 CharacteristicsoftheShortCircuitCurrent 29
2.1.1 TransientDirectCurrentComponent 30
2.1.2 TheVolt-TimeAreaConcept 32
2.1.3 TransientAlternatingCurrentComponents 35
2.1.4 AsymmetryofThreePhaseShortCircuitCurrents 36
2.1.5 MeasuringAsymmetricalCurrents 39
2.2 CalculationofShortCircuitCurrents 42
2.2.1 TheperUnitMethod 43
ix
