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FaultLocationonTransmissionandDistributionLines

FaultLocationonTransmissionandDistribution Lines

PrinciplesandApplications

SwagataDas

SuryaSantoso

SundaravaradanN.Ananthan

Thiseditionfirstpublished2022

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Names:Das,Swagata,author.|Santoso,Surya,author.|Ananthan, SundaravaradanN,author.

Title:Faultlocationontransmissionanddistributionlines:principles andapplications/SwagataDas,SuryaSantoso,Sundaravaradan N.Ananthan.

Description:Hoboken,NJ:Wiley,2022.|Includesbibliographical referencesandindex.

Identifiers:LCCN2021030668(print)|LCCN2021030669(ebook)|ISBN 9781119121466(cloth)|ISBN9781119121473(adobepdf)|ISBN 9781119121497(epub)

Subjects:LCSH:Electricfaultlocation.|Powertransmission.

Classification:LCCTK3226.D31732022(print)|LCCTK3226(ebook)|DDC 621.319/2–dc23

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LCebookrecordavailableathttps://lccn.loc.gov/2021030669

CoverDesign:Wiley

CoverImage:©REDPIXEL.PL/Shutterstock

Setin9.5/12.5ptSTIXTwoTextbyStraive,Chennai,India

10987654321

Preface ix AbouttheCompanionWebsite xi

1Introduction 1

1.1PowerSystemFaults 1

1.2WhatCausesShuntFaults? 4

1.3AimandImportanceofFaultLocation 16

1.4TypesofFault-LocatingAlgorithms 19

1.5HowareFault-LocatingAlgorithmsImplemented? 21

1.6EvaluationofFault-LocatingAlgorithms 25

1.7TheBestFault-LocatingAlgorithm 26

1.8Summary 26

2SymmetricalComponents 27

2.1Phasors 28

2.2TheoryofSymmetricalComponents 29

2.3InterconnectingSequenceNetworks 31

2.4SequenceImpedancesofThree-PhaseLines 36

2.5ExerciseProblems 41

2.6Summary 46

3FaultLocationonTransmissionLines 49

3.1One-EndedImpedance-BasedFaultLocationAlgorithms 49

3.1.1SimpleReactanceMethod 52

3.1.2TakagiMethod 54

3.1.3ModifiedTakagiMethod 56

3.1.4CurrentDistributionFactorMethod 57

3.2Two-EndedImpedance-BasedFaultLocationAlgorithms 58

3.2.1SynchronizedMethod 59

3.2.2UnsynchronizedMethod 60

3.2.3UnsynchronizedNegative-SequenceMethod 61

3.2.4SynchronizedLineCurrentDifferentialMethod 62

3.3Three-EndedImpedance-BasedFaultLocationAlgorithms 62

3.3.1SynchronizedMethod 63

3.3.2UnsynchronizedMethod 65

3.3.3UnsynchronizedNegative-SequenceMethod 66

3.3.4SynchronizedLineCurrentDifferentialMethod 67

3.4Traveling-WaveFaultLocationAlgorithms 68

3.4.1Single-EndedTravelingWaveMethod 69

3.4.2Double-EndedTraveling-WaveMethod 71

3.4.3ErrorSources 71

3.5ExerciseProblems 77

3.6Summary 93

4ErrorSourcesinImpedance-BasedFaultLocation 95

4.1PowerSystemModel 95

4.2InputDataErrors 96

4.2.1DCOffset 97

4.2.2CTSaturation 99

4.2.3AgingCCVTs 101

4.2.4Open-DeltaVTs 101

4.2.5InaccurateLineLength 104

4.2.6UntransposedLines 104

4.2.7VariationinEarthResistivity 106

4.2.8Non-HomogeneousLines 107

4.2.9IncorrectFaultTypeSelection 109

4.3ApplicationErrors 109

4.3.1Load 109

4.3.2Non-HomogeneousSystem 111

4.3.3Zero-SequenceMutualCoupling 111

4.3.4SeriesCompensation 118

4.3.5Three-TerminalLines 119

4.3.6RadialTap 120

4.3.7EvolvingFaults 121

4.4ExerciseProblems 122

4.5Summary 126

5FaultLocationonOverheadDistributionFeeders 129

5.1Impedance-BasedMethods 134

5.1.1LoopReactanceMethod 135

5.1.2SimpleReactanceMethod 140

5.1.3TakagiMethod 140

5.1.4ModifiedTakagiMethod 141

5.1.5Girgisetal.Method 141

5.1.6Santosoetal.Method 143

5.1.7Novoseletal.Method 144

5.2ChallengeswithDistributionFaultLocation 146

5.2.1Load 146

5.2.2Non-HomogeneousLines 146

5.2.3InaccurateEarthResistivity 149

5.2.4MultipleLaterals 150

5.2.5BestDataforFaultLocation:FeederorSubstationRelays 151

5.2.6DistributedGeneration 152

5.2.7HighImpedanceFaults 156

5.2.8CTSaturation 156

5.2.9Grounding 156

5.2.10ShortDurationFaults 157

5.2.11MissingVoltage 157

5.3ExerciseProblems 158

5.4Summary 177

6DistributionFaultLocationWithCurrentOnly 179

6.1CurrentPhasorsOnlyMethod 179

6.2CurrentMagnitudeOnlyMethod 184

6.3Short-CircuitFaultCurrentProfileMethod 191

6.4ExerciseProblems 193

6.5Summary 208

7SystemandOperationalBeneﬁtsofFaultLocation 209

7.1VerifyRelayOperation 210

7.2DiscoverErroneousRelaySettings 211

7.3DetectInstrumentTransformerInstallationErrors 217

7.4ValidateZero-SequenceLineImpedance 222

7.5CalculateFaultResistance 225

7.6ProveShort-CircuitModel 226

7.7AdaptAutoreclosinginHybridLines 227

7.8DetecttheOccurrenceofMultipleFaults 228

7.9IdentifyImpendingFailuresandTakeCorrectiveAction 232

7.10ExerciseProblems 232

7.11Summary 239

AFaultLocationSuiteinMATLAB 241

A.1UnderstandingtheFaultLocationScript 241

References 261 Index 269

Preface

Thepurposeofthepowersystemistoistodeliverelectricalpowerfromgeneratorstoloads throughtransmissionanddistributionlines.Today,electricalpowerisanecessityofeverydaylifeandisexpectedtobepresentwheneverweneedit.Unfortunately,thisexpected servicemaynotalwaysbeavailable,particularlywhenthereisashort-circuitfaultonthe powersystem.Theoutagetimewillequalthetimetakenbytheutilitytofindthefaultplus thetimetakentomakerepairs.

Fault-locatingalgorithmscanshortenthetimetakentofindfaultsontransmissionand distributionlines.Theselinescoverlongdistances.Manuallypatrollingthelinetolocate thefaultcanbequitetimeconsuming.Roughterrainsandbadweathercanmakeitthat muchhardertolocatethefault.Knowingwheretolookforthefaultsavessignificanttime andexpediteservicerepairandrestoration.

Today,therearemanyfault-locatingalgorithmstochoosefrom.Whileallalgorithmshave thesameobjective,whichistofindthefaultwiththehighestaccuracy,eachalgorithm makesdifferentassumptionsandusesdifferentdatatoarriveatthisresult.Whatisthe bestfault-locatingalgorithm?Thecorrectansweristhatitdepends.Itdependsonthedata availableforfaultlocation,thesystemtowhichthealgorithmwillbeappliedto,andthe natureofthefault.

Thepurposeofthisbookistoexplainhowthedifferentfault-locatingalgorithmswork, identifywhatdatatheyneed,anddiscussthesourcesoferror.Thisinformationcanhelp thereadermakeaninformeddecisionaboutwhatisthebestfault-locatingalgorithmfor theirsystem.Severalreal-worldexamplesarepresentedthatshowhowtoapplythesealgorithmstofaulteventdataandsolveforthefaultlocation.Thebookalsocoverstheadditional benefitsoffaultlocationthatcanhelpimprovepowersystemperformanceandreliability.

Wehopethatpracticingengineersandstudentswillfindthisbookhelpful.Pleasefeel freetoreachouttousifyouhaveanycommentsforimprovementorfindanyerrors.

Finally,wewouldliketosincerelythankElectricPowerResearchInstituteforgivingus faulteventdatausedinthisbook.

29October2021

SwagataDas SanAntonio,Texas

SuryaSantoso Austin,Texas

SundaravaradanN.Ananthan Houston,Texas

AbouttheCompanionWebsite

Thisbookisaccompaniedbyacompanionwebsite: www.wiley.com/go/das/faultlocation

Thewebsiteincludesthefollowingmaterials: ● FaultLocationSuiteinMATLAB

Introduction

Thepowersystemisacomplexnetworkofgenerators,transformers,transmissionlines, distributionfeeders,loads,andotherelectricalcomponents.Thepurposeofthisnetworkis todeliverelectricalpowerfromgeneratorstoloadsthroughtransmissionlinesanddistributionfeeders.Today,electricalpowerisanecessityofeverydaylifeandisexpectedtobe presentwheneverweflipthelightswitch,chargeourphones,andturnonothergadgets. Unfortunately,thisexpectedservicemaynotalwaysbeavailable,particularlywhenthere isafaultonthepowersystem.

Faultsareabnormalconditionsonthepowersystemthatdisruptthenormalflowofelectricalpowerfromgeneratorstoloads.Lightning,animalcontact,treecontact,andadverse weathersuchasstrongwindsandwinterstormsaresomeofthemajorreasonsforpower systemfaults.Utilitiestakemanypreventivestepssuchasinstallingshieldwiresandsurge arresterstodiverttheenergyoflightningstrikes,puttingupanimalguards,andtrimming treesatperiodicintervalstominimizethechancesofafault.Inspiteofallthesemeasures, faultsareinevitableonthepowersystem.Sowhentheyoccur,alleffortsmustbemadeto locatethefaultasquicklyaspossible,makerepairs,andrestorepower.Thisiswhyfault locationissoimportantandcriticaltoimprovingpowersystemreliability.

Webeginthischapterbyexplainingthetypesoffaultsthatcanoccuronthepowersystem andtheirrootcause.Wethenmoveourfocustofault-locatingalgorithms.Wediscusstheir aimandimportance,theirprinciples,theirimplementationinthefield,andtheirevaluation criteria.Finally,wediscusshowtochoosethebestfault-locatingalgorithmfromamongthe manyalgorithmsthathavebeenproposedintheliterature.

1.1PowerSystemFaults

Faultsareabnormalconditionsonthepowersystemthatcausevoltage,current,frequency, andpowertodeviatefromtheirnominalvalues.Protectiverelaysaretypicallyusedtodetect andisolatethesefaultsasquicklyaspossibletoreturnthepowersystembacktonormal operatingconditions.TheInstituteofElectricalandElectronicsEngineers(IEEE)defines aprotectiverelayas“adevicewhosefunctionistodetectdefectivelinesorapparatusor otherpowersystemconditionsofanabnormalordangerousnatureandtoinitiateappropriatecontrolaction”[1].Protectiverelaysusecurrenttransformers(CTs)andpotential

FaultLocationonTransmissionandDistributionLines:PrinciplesandApplications,FirstEdition. SwagataDas,SuryaSantoso,andSundaravaradanN.Ananthan. ©2022JohnWiley&SonsLtd.Published2022byJohnWiley&SonsLtd. Companionwebsite:www.wiley.com/go/das/faultlocation

transformers(PTs)tomonitorthestateofthepowersystem.Whenafaultisdetected,they sendatripcommandtocircuitbreakers,whichthenopentoisolatethefault.Inlow-voltage distributionsystems,fusesareoftenusedinsteadofprotectiverelaysandcircuitbreakers todetectandisolatefaultsthatcreateanovercurrentcondition.AfuseisdefinedbyIEEE as“anovercurrentprotectivedevicewithacircuit-openingfusiblepartthatisheatedand severedbythepassageoftheovercurrentthroughit.”

Faultsexperiencedbythepowersystemcanbeoftwotypes,seriesfaultsandshunt faults.Seriesfaultsusuallyoccurwhenthereisanopencircuitononeortwophase conductorsduringloadconditions.Becausetheopencircuitoccursinserieswiththe phaseconductor,thesefaultsareknownasseriesfaults.Seriesfaultscanbecausedby brokenjumpersorwhenallthreepolesofacircuitbreakerpoleareunabletocloseduring amanualoranautomaticcloseoperation.Theycanalsobecausedbyablownfuse.For example,Fig.1.1showsadistributiontransformerbeingprotectedbyhigh-sidefuses. Ifoneortwohigh-sidefuseblowsduetoanovercurrentcondition,itwillresultinaseries fault.Duringaseriesfault,thecurrentinthefaultedphasedecreasesduetolossinload whilethehealthyphasecontinuestocarryloadcurrent.Thevoltageandfrequencyof thefaultedphasealsoincreaseascomparedtothehealthyphase.Whileseriesfaultsdo notresultinhighmagnitudecurrentstoflowinthefaultedphases,theymakethepower systemunbalanced,causingunbalancedcurrentstoflowinthepowersystem.Theheat generatedbytheunbalancedcurrentscandamagetransformersandmotors.References [2–4]explainhowprotectiverelayscanbesetuptodetectandisolateseriesfaults.

Shuntfaultsoccurwhenthereisashuntconnectionbetweenoneormorephaseconductorstothegroundorbetweeneachother.Theshuntconnectioncreatesashort-circuit conditionallowingcurrenttoflowthroughanalternate,lowerimpedancepath.Thelower impedancecausesthecurrentinthefaultedphasetodramaticallyincreasewhilethevoltage ofthefaultedphasedecreases.Becauseshuntfaultsaremorecommonandmoredamaging thanseriesfaults,thisbookwillfocusonlocatingshuntfaults.

Therearefourtypesofshuntfaults(seeFig.1.2).Singleline-to-groundfaults(also referredtoassinglephase-to-groundfaults)occurwhenoneofthethreephaseconductors makescontactwiththegroundwireorthegroundedpieceofanequipment.Seventyto eightypercentofallfaultsaresingleline-to-groundfaults,makingthisthemostcommon faulttype[5].Line-to-linefaults(alsoreferredtoasphase-to-phasefaults)occurwhen twophaseconductorsmakecontactwitheachother.Doubleline-to-groundfaults(also referredtoasdoublephase-to-groundfaults)occurwhentwophaseconductorsmake contactwitheachotherandthegroundwireorthegroundedpieceofanequipment. Three-phasefaultsoccurwhenallthreephaseconductorsmakecontactwitheachother,

Figure1.1 Adistributiondelta/wye-groundedtransformerbeingprotectedbyhigh-sidefuses. Ablownfusewillresultinaseriesfault.

Figure1.2 Thefourtypesofshuntfaults.

withorwithoutgroundconnection.Thisfaulttypeisquiterareandismostoftenthe resultofhumanerrors.Three-phasefaultsarereferredtoasbalancedfaultsasthefault involvesallthreephases.Theotherfaulttypesinvolveoneortwophasesandmakethe powersystemunbalanced.Asaresult,theyarereferredtoasunbalancedfaults.

Shuntfaultscanbepermanent(leadingtosustainedoutages)ortemporary(leadingto momentaryoutages).Permanentfaultsoccurwhenthereispermanentdamagetoapower systemequipmentandrequirelinecrewtomakerepairsbeforereenergization.Temporary faultsoccurduetolightning,animalcontact,flyingdebris,andothertemporarysources offault.Suchfaultsclearoutontheirownafterthefaultarcgetsextinguished.Whenthe arcgetsextinguishedbyitselfwithouttheoperationofanyprotectivedevice,thefaultis referredtoasaself-clearingfault.Thesefaultsgenerallyoccurwheninsulationbreaksdown nearthevoltagepeakbutclearoutontheirownwithinaquartercycle.Thefrequencyof self-clearingfaultsincreaseovertimeandeventuallyleadtopermanentfaults[6].Faultarcs canalsogetextinguishedbytheoperationofarelayandcircuitbreaker.Afterashortopen timedelay,whichallowsthearctogetextinguished,therelaysendsareclosecommand tothecircuitbreakertoresumenormaloperation.Mostfaultsonundergroundcablesare permanentfaults.Incontrast,mostfaultsonoverheadsystemsaretemporaryfaults[7].

Shuntfaultscancausesignificantthermaldamagetopowersystemequipment.Thermal energyduringafaultisproportionaltothemagnitudeanddurationofthefaultcurrent. Ifthisthermalenergyexceedsthethermallimitofpowertransformers,motors,andother powersystemequipment,theygetdamagedduetoinsulationfailure.Inaddition,strong mechanicalforcesdevelopedbythehighmagnitudecurrentcanbreakandphysicallydamagepowersystemequipment.Infact,[8]reportsthattransformers,acriticalassetinthe substation,mostoftenfailduetomechanicalandthermalstresscausedbyexternalthrough faults.Shuntfaultsarealsoasafetyconcern.Sparksfromfaultscanstartforestfires.Faults insideoil-filledtransformerscanleadtofiresandexplosions,creatingdangerousworking conditionsforpersonnelinsidethesubstation.Arcflasheventsinaswitchgearcanleadto dangerousandpossiblyfatalconditionsduetoheat,ultravioletradiation,shrapnel,noise, andpressurefromtheblast[9].Shuntfaultsifnotclearedbeforethecriticalclearingtime canmakethepowersystemunstable,leadingtocascadingoutages[10].Finally,shuntfaults cancausevoltagesagsorswellsonotherhealthyfeeders.Avoltagesagisdefinedasan eventinwhichthermsvoltagedropstoavaluebetween0.1and0.9perunitforaduration

Figure1.3 Voltagesagduetoasingleline-to-groundfaultona138kVline. betweenahalfcycletooneminute.Anexampleofvoltagesagduringasingleline-to-ground faultisshowninFig.1.3.Voltagesagisapowerqualityeventthatcanshutdownsensitive equipmentinindustrialplants,resultinginarevenuelossofseveralmilliondollars.Voltage swellisdefinedasaneventinwhichthermsvoltageincreasestoavaluebetween1.1and 1.8perunitforadurationbetweenahalfcycletooneminute.Thiscanoccurwhensingleline-to-groundfaultsoccuronanungroundedsystem.Voltageoftheunfaultedphases swellsto1.73perunitandstressestheinsulators.Forallthereasonslistedabove,shunt faultsmustbedetectedandisolatedasfastaspossible.Thelatestgenerationofprotective relayscandetectfaultsinasfastas2ms[11].Thebreakertakesanadditionaltwoorthree cyclestoopen.Thefastclearingtimelimitsthedamagetopowersystemequipment,reduces theimpactofthefaultontherestofthepowersystem,andincreasespersonnelsafety.

1.2WhatCausesShuntFaults?

Thissectiondiscussesthemostcommoncausesofshuntfaultsonthepowersystem. Lightning Lightningisamajorcauseofshuntfaultsonthepowersystem.DatacollectedbyTexas ReliabilityEntityshownsummarizedinFig.1.4isacaseinpoint.Youcanseethatlightning

Figure1.4 Shuntfaultson345kVtransmissionlinesinTexasin2015categorizedbyroot cause[18].

MomentaryoutageSustainedoutage JanFebMarAprMayJunJulAugSepOctNovDec

Figure1.5 Acomparisonofthenumberofsustainedandmomentaryoutageson345kV transmissionlinesinTexasin2015[18].

wasresponsibleforalargenumberoffaultson345kVtransmissionlinesinTexasin2015, particularlyduringthemonthsofApril,May,andOctober.Figure1.5showshowmanyof thesameshuntfaultsresultedinsustainedandmomentaryoutages.Duringthemonthsof April,May,andOctober,whenlightningactivityhaddramaticallyincreased,thenumber ofmomentaryoutageswasmuchgreaterthanthenumberofsustainedoutages.Thedata establishesastrongcorrelationbetweenlightningandmomentaryoutages,indicatingthat mostfaultsduetolightningaretemporaryfaults.

Figure1.6 LocationofNLDNsensorstodetectlightning[14].

LightningactivityintheUSismonitoredbytheNationalLightningDetectionNetwork (NLDN).Thisnetwork,ownedandoperatedbyVaisala,hasoverahundredsensorsacross theUSasshowninFig.1.6.Duringalightningstrike,sensorsthatgettriggeredsendthe informationtheycapturedaboutthestrikeviasatellitetoacentrallocationinTucson, Arizona.There,datafromdifferentsensorsarecombinedtoestablishdate,time,peak currentmagnitude,type,andlocationofthelightningstrike[13].Thedataisthenmade availabletotheNationalWeatherServiceandutilitiesthatsubscribetothisservice.These utilitiescanmakeuseofthisinformationtodeterminewhetherlightningwasinthearea whenaparticularfaultoccurredontheirsystemandwhetheritwastherootcauseofthe fault.

Lightningoccurswhenathundercloud(alsoreferredtoasacumulonimbuscloud)developsareasofpositiveandnegativechargesasshowninFig.1.7.Lightningdischargecan occurbetweenthepositivelychargedandthenegativelychargedregionsinsidethecloud andarereferredtoasintracloudlightning.Itcanalsooccurbetweenthepositivelycharged

Lightningdischargescanbeintracloud,cloud-to-cloud(intercloud),cloud-to-air,and cloud-to-ground[14].

Cloud-toCloud

Figure1.7

areaofonethundercloudandthenegativelychargedareaofanotherthundercloudandis referredtoascloud-to-cloudorintercloudlightning.Lightningcanalsooccurbetween athundercloudandair,referredtoasacloud-to-airlightningdischarge,andbetweena thundercloudandtheearth,referredtoasacloud-to-grounddischarge.Cloud-to-ground dischargesconstituteabouttwenty-fivepercentofalllightningdischargesandaretheones responsibleforcreatingshuntfaultsonthepowersystem.

Figure1.8showsfourdifferentwaysbywhichacloud-to-groundlightningstrikecan occur.Adownwardnegativelightningstrikestartswhennegativechargesatthelowerparts ofthecloudstartionizingtheair.Thisresultsinacolumnofnegativecharges,knownasthe leader,movingdowntowardtheground.Astheleaderapproachestheground,itinduces streamersofoppositechargestomoveupfromtheground.Whentheleaderandstreamer makecontactwitheachother,thepathbecomescomplete,acloud-to-groundstrikeoccurs, andahugeamountofnegativechargeistransferredtotheground.Adownwardpositive lightingstrikeoccursthesamewayasthepreviousone,exceptthattheleaderisinitiated bypositivechargesinthecloud.Upwardlightningstrikesoccurwhenleadersareinitiated bytallobjectsonthegroundwithsharpcorners.Whentheleaderreachesthecloud,a cloud-to-groundlightningstrikeoccurs.Whentheleaderispositive,itiscalledupward positivelightning.Whentheleaderisnegative,itiscalledupwardnegativelightning. Outofthefourtypes,downwardnegativecloud-to-groundlightningstrikesaremore common.

Figure1.8 Typesof cloud-to-groundlightning[14].

Figure1.9 Overvoltageduetolightningstrikeona69kVtransmissionlineresultedinaﬂashover andaphase-to-groundfault.Theinsulatorstringwasfoundtobedamagedwithmultipleceramic disksmissing.(Photo:CourtesyofMr.GenardoCorpuz,LowerColoradoRiverAuthority,USA.)

Acloud-to-groundlightningstrikecancreatefaultswhenitdirectlystrikesaphaseconductorandinjectsahugecurrentsurgeintotheline.Thecurrentsurgeisaccompanied byavoltagesurge.Ifthevoltagesurgeexceedstheinsulatorcriticalflashovervoltage,a flashoverwilloccur,resultinginashuntfault.Lightningcanalsostrikeatowerandcreate faults.Whentheinjectedcurrentsurgetravelsthroughthetowertotheground,avoltage risedevelopsacrossthetowercrossarmduetothesurgeimpedanceofthetowerandthe towerfootingresistance.Ifthevoltageriseislargeenough,aflashoverwilloccurfromthe towertotheconductoracrosstheinsulatorstring.Thisflashover,commonlyreferredto asbackflash,willcreateashuntfault.Figure1.9,Figure1.10,andFigure1.11showthe damagetoutilityassetsduetoflashoverduringlightning.

Toprotectpowersystemequipmentfromlightningatsubstations,lightingmasts(shown inFig.1.12)andlightningarrestersareused.Linearrestersareusedinparallelwithtransmissionlineinsulatorstopreventthevoltagefromincreasingbeyondthelineinsulation level.Toreducethepossibilityofdirectlightningstrikestotransmissionlines,groundwires (shieldwires)areoftenplacedabovethephaseconductors(showninFig.1.13).Shieldwires alsoreducethepossibilityabackflashastheinjectedcurrentisdividedintothreeparts (towerandeachdirectionontheshieldwire).Polegroundisimprovedbydrivingametal rodfurtherdownintotheground.

Animals

Animalssuchasbirds,snakes,monkeys,cats,andsquirrelsarenotoriousforcreatingfaults onthepowersystem.Figure1.14showsamonkeythatdiedaftermakingcontactwith

Phase flashed to ground at this point

Wire that connects arm/bracket to the ground wire has melted

Figure1.10 Anotherexampleofafaultduetolightningstrikeona138kVtransmissionline. TheresultingovervoltagecausedaﬂashoverandanA-Gfault.Noticethedamagetotheconcrete toweratthepointoftheﬂashover.Partofthewirethatconnectsthebracket/towerarmtothe groundwirehaseithermeltedorblownaway.(Photo:CourtesyofMr.GenardoCorpuz,LowerColorado RiverAuthority,USA.)

Ground wire

Flashover point of one phase

Flashover point of the other phase

Figure1.11 Similartothepreviousexample,lightningstrucka138kVtransmissionline.PhaseA andphaseCﬂashedtothegroundwireandcreatedaline-to-linefaultthroughthegroundwire. Noticetheevidenceofdamagetotheconcretetowerwhenoneofthephasesﬂashedovertothe groundwire.(Photo:CourtesyofMr.GenardoCorpuz,LowerColoradoRiverAuthority,USA.)

Broken ground wire

Lightning mast

Figure1.12 Lightningmastatasubstation.

Figure1.13 Shieldwireonasingle-circuit 345kVtransmissionline.(Photo:Courtesyof Mr.GenardoCorpuz,LowerColoradoRiver Authority,USA.) Shield wire

energizedequipmentinasubstationandcreatingafault.Figure1.15showsthedamage toa22kVbreakerwhenabirdflappeditswings,touchedbothBandCphases,andcreated aBCfault.Birdsbuildnestsontransmissiontowers,ondistributionpoles,andinsubstations.Thesenestscancauseashortcircuitbymakingcontactwithmultipleconductors. Theycanalsoattractotheranimalssuchassnakesandraccoonsthatinturncausefaults. Birddroppingscontaminateinsulatorsandcanresultinaflashover.Woodpeckerscancause structuraldamagetowoodenpoles.Horses,bears,bison,andcattlecanalsodegradethe structuralintegrityofpolesbyrubbingagainstguy-wires,causingthepolestoleanandconductorstosag.Squirrelscanclimbutilitypolesandcreatefaultsbybridgingthegapbetween phaseconductorsandthegroundedequipment.Smallanimalssuchasratsandmicecan chewontheinsulationofundergroundcablesandcreatefaults.Toreducethenumberof

Figure1.14 Amonkeythatmadecontactwithenergizedequipmentinasubstationandcreateda fault.(Photo:CourtesyofMr.EmmanuelRaubenheimer,Eskom,SouthAfrica.)

Figure1.15 AbirdﬂappeditswingsandbridgedthegapbetweenphaseBandphaseCbushing onthebussideofa22kVbreaker,creatingaBCfault.Thefaultcurrentmagnitudewasabout2kA. Theline-to-linefaultlaterevolvedintoathree-phasefault.Italsoﬂashedacrossthebreakerand createdaB-Gfaultonthe22kVdistributionfeeder,justinfrontofthebreaker.Flashmarksare clearlyvisibleontheclampsandonthebushingsofthebreaker.(Photo:CourtesyofMr.Emmanuel Raubenheimer,Eskom,SouthAfrica.)

Bird caused a B-C Fault

Figure1.16 Birdspikestopreventbirdsfromperching.

faultsduetobirds,someutilitiesinstallbirdspikessuchastheoneshowninFig.1.16to discouragebirdsfromperchingorroosting.Anotherpreventivestepistowashtheinsulatorsatperiodicintervalstoremovebirddroppingsandothercontaminants.Animalguards suchastheoneshowninFig.1.17arealsoinstalledaroundenergizedequipmenttorestrict animalcontact.

Animalguardaroundthetopofthetransformerlowvoltagebushing.

Trees

Treesareresponsibleforalargenumberofpowersystemfaults.Infact,atreewasresponsibleforthefaultthattriggeredtheNortheastblackoutof2003,oneofthemajorblackoutsin NorthAmerica’shistory[15].Treescancausefaultsinanumberofways.Thoseuprooted byheavywindsorhurricanescanteardownlines,knockdownpoles,ordamageinsulators whenfallingdown.Overgrownvegetationcanbridgephaseconductors.Treelimbsbroken duringheavywindscanflyintoalineandbridgephaseconductors.Treebranchesblown bythewindcanpushtwoconductorstogether.Linesmaysagduringheavyloadconditionsandondoingsomaymakecontactwiththeunderlyingvegetation.Electricutilities typicallyhaveavegetationmanagementprogramtotrimtreesandpreventtree-relatedoutagesandwildfires.Theymayalsomodifyspacingbetweenphaseconductorstoincreasethe resistancetoflashover.

OtherCauses

Powersystemfaultscanbecausedbyaccidentssuchaswhenvehiclescrashintopolesor whendrones,kites,shinyfoilballoons,andhotairballoonsmakecontactwithenergized

Animal Guard

Figure1.17

conductors.SuchanunfortunateeventoccurredonJuly30,2017,whenahot-airballoon struckhigh-voltageconductors,killingallsixteenpeopleaboard[16].Afaultcanalsooccur duetohumanerrorssuchasforgettingtoremovethegroundingchainsaftermaintenance andclosingthebreaker.Faultscanalsooccurduringactsofvandalism.Theyinclude thievesstealingconductorwiretolatersellasscrapmetalorpeopleshootingatinsulators witharifle.AnexampleofvandalismoccurredonApril16,2013,whentherewasasniper attackontheMetcalftransmissionsubstationownedbyPacificGasandElectric[17]. Snipersopenedfireonseventeentransformers,causingseveredamageandforcinggrid officialstoreroutepowerfromnearbypowerplantstoavoidablackout.Inaddition, contaminantscanalsoweakentheinsulatorsovertime,resultinginaflashoveranda short-circuitfault.Thisisaproblemparticularlyincoastalareaswherecontaminants suchasdustandsaltorinagriculturalareaswherecontaminantssuchaspesticideand fertilizerbuildupovertime,eventuallyleadingtoafault.Strongwindscancausepower linestoswingintooneanotherandcreatefaults.Severewindsduringhurricanesand tornadoescanevenbreakpowerlinesandutilitypoles,creatingsignificantdamageto thepowersysteminfrastructure.Snowandicearealsoamajorcauseoffaults.Their weightcancausepowerlinestosnaportreelimbstobreakandfallintoutilitylines. Powersystemequipmentcanalsofailinternallyandcreateafault.Theinternalfault maybetheresultofaninsulationfailureduetoage,overvoltage,andotherfactors. Figure1.18showwhenaregulatorfailedinasubstationandcausedsignificantdamage. Figure1.19showsanotherexamplewhentherewasafaultinsideacapacitorbankdueto overvoltage.

Figure1.19 Internalfaultinsideacapacitorbankinasubstationduetoovervoltage.

(Photo:CourtesyofMr.LongTran,SouthTexasElectricCooperative,USA.)

1.3AimandImportanceofFaultLocation

Thepurposeofthepowersystemistodeliverelectricpowerfromgeneratorsinpower plantstoindustrialplantsandresidentialcustomersthroughaninterconnectednetwork oftransmissionlinesanddistributionfeeders.Figure1.20showsaturbineandgenerator insideasteampowerplant.Steamproducedbyheatingwaterisusedtorotatetheturbine. Thisturbinecoupledtoanelectricgeneratortransformsthemechanicalpowertoelectrical powerwithavoltagebetween5and34.5kV.Totransportelectricalpoweroverlong distanceswithminimumloss,thevoltageissteppeduptobetween69and765kVusing step-uptransformersasshowninFig.1.21.Theelectricalpoweratastepped-upvoltageis