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Dieselgeneratorprotectionrelay

5/14/2015 Zone4info.comDieselgeneratorprotectionrelay

http://zone4info.com/forums/topic/6603/dieselgeneratorprotectionrela#.VVOWbmqpHw 3/5

SarahOkwuosa

5postsApril30,201512:13AMEESTReply&attachImageQuoteReport

Iamdoingadieselgeneratorprotectionrelaysetting.Wenormallysetthe51Vto1.4xFullloadcurrent.Onthegeneratornameplate,themaximumoverloadis10%for2hours.Isthe1.4Fullloadsettingtoohigh?

AlexdeMoura

267postsMay1,20156:59PMEESTReply&attachImageQuoteReport

Sarah,greetings,Ican'tsaymuchwiththelittleinformationyougave,butlet'strytohelpyouonthis.

ThefrontlineovercurrentprotectionismadebytheInstantaneous50orTimed51relays/functions,meanwhilethe51VistheVoltageSupervised(Timed)Overcurrent.ItisabackuprelaythatworksonlyatGeneratorundervoltageconditions,usuallyinLVandMVGenerators.The51Vcanbe:

1.VoltageRestrainedOvercurrent:sometimescalled51VR,theovercurrentsetting

Ease guaranteedWall hung electric Water heaters

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CHANGESasthevoltagechanges,allowingittorespondtoovercurrentsatallreducedvoltages,thereisSetPointCurve(%SPx%Vr),itisacontinuous/analogrelay.Atratedvoltage(Vr)thesettingis125175%FLC,verycommon,but125150%FLAisalsousual.TheSetPointof140%FLCofyoursisinsideofbothoptions,ifweassumeVrcondition.Forothervoltages,the51VRSetPointcurvetypicallystarts25%SP@0%Vr(inyourcase25%SP=25%x140%FLC=35%FLC)butIprefertoadjust30%SP@20%Vr(inyourcase30%SP=30%x140%FLC=42%FLC),inamorelinearpartofthecurve

2.VoltageControlledOvercurrent:sometimescalled51VCor51C,theovercurrentsettingisENABLEDwhenthevoltageisbelowapresetvalue.Ifthevoltageisabovetheundervoltageelementsettingtherelayisnotfunctional,soitisadiscreterelay.Theundervoltagesettingtoenablethe51VCis70%90%Vr,75%Vrisveryusual,or5%morethantheUndervoltageProtectionRelaysettingisalsocommon

SomeEngineersliketouse8090%Idovercurrentsetting,mainlyfor51VCtype,beingId=1/XdSynchronousUnsaturated.ButIsupposethisaddsmorecomplications.IfyouhaveIdavailableyoucanuseittocheckiftheovercurrentsettingisinthe8090%Idrange.

Thetimesettingfor51Vcanbe0.52.0secondsnormally,beingthe1.0secondthemostusualvalue,orthesametimesettingtobeappliedon51TimedOvercurrentrelay.

Ifyouarereallyuncomfortablewith140%FLC,youcanreducetosomethinglike135%FLC,butIwouldnotsuggestthatbecausetheGeneratorhasacontinuousoperation(morethan1hour)capabilityof110%FLC,asyoudescribed.ThatiswhysomeEngineersuseFLA(practical,measured)insteadofFLC(theoretical,rated)for51Vsettingcalculationsas125150%FLA.YourGeneratorhasaFLA=110%FLC.Areducedsettingforabackup51Vrelaycouldmakeitoperatetoooftenandinconvenientlybeforeotherfrontlineovercurrentprotections.

Ithink140%FLCisOK,andIwoulddaretosaythatmaybeyouwillincreasethisvalueabitduringprojectCommissioningafterthetestsindicatesomeunwantedtripsbyovercurrent,mainlyatoverloadoperations.Pleaseletusknowaboutit.

ThispostwaseditedbyAlexdeMouraatMay3,201511:31PMEEST

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