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外文资料翻译ReliabilityofLightningResistantOverheadDistributionLinesLightingcontinuestobethemajorcauseofoutagesonoverheadpowerdistributionlines.Throughlaboratorytestingandfieldobservationsandmeasurements,thepropertiesofalightningstrokeanditseffectsonelectricaldistributionsystemcomponentsarewell-understoodphenomena.Thispaperpresentsacompilationof32yearsofhistoricalrecordsforoutagecauses,duration,andlocationsforeightdistributionfeedersattheOakRidgeNationalLaboratory(ORNL).Distributiontypelightningarrestersareplacedatdead-endandanglestructuresatpolemountedwormerlocationsandathighpointsontheoverheadline.Stationclasslightningarrestersareusedtoprotectundergroundcableruns,padmountedswitchgearandunitsubstationtransformers.Resistancetoearthofeachpolegroundistypically15ohmsorless.Athigherelevationsinthesystem,resistancetoearthissubstantiallygreaterthan15ohms,especiallyduringthedrysummermonths.Atthesehighpoints,groundrodswererivenandbondedtothepolegroundingsystemsinthe1960'sinanattempttodecreaselightningoutages.Theseattemptswereonlypartiallysuccessfulinloweringtheoutagerate.Fromasurgeprotectionstandpointthevarietyofpolestructuresused(in-line,corner,angle,deadend,etc.)andthevarietyofinsulatorsandhardwareuseddoesnotalloweach13.8kVoverheadlinetobecategorizedwithauniformimpulseflashoverrating(170kV,etc.)oranumericalBILvoltageclass(95kVBIL;etc.).Forsimplicitypurposesintheanalysis,eachoverheadlinewascategorizedwithanominalvoltageconstructionclass(15kV,34kV,or69KV).Sixoftheeightoverheadlines(feeders1through6)werebuiltwithtypicalREAStandardhorizontalwoodcrossarmconstructionutilizingsingleANSIClass55-5porcelainpininsulators(nominal15kVinsulation).Theshieldangleoftheoverheadgroundwiretothephaseconductorsistypically45degrees.Oneoverheadline(feeder7)wasbuiltwithtransmissiontypewoodpoleconstructionbecausethelineextendedtoaresearchfacilitywhichwastohavegeneratedelectricalpowertofeedbackintothegrid.PolestructureofthislineareofdurablewoodcrossaconstructionwhichutilizedoubleANSI52-3porcelainsuspensioninsulatorstosupporttheconductors(nominal34kVinsulation).Theshieldangleoftheoverheadgroundwiretothephaseconductorsforfeeder7istypically30degrees.In1969,anoverheadline(feeder8)wasintentionallybuiltwithlightningresistantconstructioninanattempttoreducelightningcausedoutages.Polestructuresofthelinehavephaseoverphase24-inchlongfiberglasssuspensionbracketswithdoubleANSI52-3porcelainsuspensioninsulatorstosupporttheconductors(nominal69kVinsulation).Theshieldangleoftheoverheadgroundwiretothephaseconductorsforfeeder8istypically30degrees.Thefailuredatawascompiledforeachoftheeight13.8kVfeedersandispresentedinTable,alongwithpertinentinformationregardingfeederconstruction,elevation,length,andage.Akeyfindingofthefailureanalysisisthatweather-relatedeventsaccountforoverhalf(56%)ofthefeederoutagesrecorded.Fifty-sevenofthe76weather-relatedoutageswereattributedtolightning.Insulationbreakdowndamageduetolightningisalsosuspectedinatleastadozenoftheequipmentfailuresobserved.Thedataindicatesoverheadlineswhichpassoverhighterrainarelessreliablebecauseofthegreaterexposuretolightning.Forexample,feeder3hadthemostrecordedoutages(48),ofwhichtwo-thirdswereduetoweather-relatedevents;thisfeederisalsothehighestlineontheplantsite,risingtoanelevationof450abovethereferencevalleyelevation.Overheadlinesthatarelongerandtowhichmoresubstationsandequipmentareattachedwerealsoobservedtobelessreliable(moreexposuretolightningandmoreequipmenttofail).Theageofthelinedoesnotappeartosignificantlylessenitsreliabilityaslongasadequatemaintenanceisperformed;noneofthelineshavehadanotableincreaseinthefrequencyofoutagesasthelineshaveaged.Aswouldbeexpected,theempiricaldatapresentedinTableIconfirmsthetwooverheadlineswhichhavebeeninsulatedtoahigherlevel(34or69KV)havesignificantlybetterreliabilityrecordsthanthoseutilizing15kVclassconstruction.Feeder7(insulatedto34KV)andfeeder8(insulatedto69kV)havebadonly3outageseachovertheir32and23yearlifespans,respectively.Theselinesfollowsimilarterrainandarecomparableinlengthandagetothe15kVclasslines,yettheyhaveacombinedfailurerateof0.22failuresperyearversus4.32failuresperyearfortheremainingfeeders.Ontypical15kVinsulatedlineconstruction,lightningflashoversoftencause60cyclepowerfollowandfeedertrip.Withthehigherinsulationconstruction,outageratesarereducedbylimitingthenumberofflashoversandtheresultantpowerfollowwhichcausesanovercurrentdevicetotrip.Thisallowslightningarresterstoperformtheirdutyofdissipatinglightningenergytoearth.Thenumberofrecloseractionsandtheirresultantmomentaryoutagesarealsoreduced.Thisisbeneficialforcriticalfacilitiesandprocesseswhichcannottolerateevenmomentaryoutages.Anadditionalbenefitisthatoutagesduetoanimalcontactarealsoreducedbecauseofthegreaterdistancefromphaseconductortogroundonpolestructures.Distributionlineequipmenttoincreaselineinsulationvaluesareofftheshelfitemsandproventechnology.Newlightningresistantconstructiontypicalbyutilizeshorizontallineposts,fiberglassstandoffbracketsoranyothermethodwhichworldincreasetheinsulationvalue.Thereplacementofsta