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Case Study - How we solved an Earth-fault (mal)Tripping that was causing complete plant tripped

Routine Maintenance and Testing of the various equipment's in the plant is one of the most important jobs, which is usually entrusted to experts. We are presenting herewith a case which makes such activities meaningful and can save the assets.<br>

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Case Study - How we solved an Earth-fault (mal)Tripping that was causing complete plant tripped

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  1. ISO 9001:2015 ISO 45001:2015 (OH & S) Certified Company Case Study How we solved an Earth-fault (mal)Tripping that was causing complete plant tripped www.systemprotection.in +91-265-2225137

  2. RoutineMaintenanceandTestingofthe variousequipment'sintheplantisoneof themostimportantjobs, whichisusually entrustedtoexperts. Wearepresenting herewithacasewhichmakessuchactivities meaningfulandcansavetheassets. Unbalancinginthethreephasecurrents canbeduetounbalanceloadingcondition also. Astheentireloadingwas3-Øandbalanced, therewasnoquestionofunbalancing. Wewereappointedtocarryouttheroutine maintenanceandtestingofthe Switchgears, Relays, CTs & PTsinoneofthe ContinuousProcessPlantsinIndia. Duringtheseactivities, oneday, the Engineer-in-Chargeinformedusthatthere isalong-pendingprobleminLTPCC IncomerFeeder, andwhetherwecansolve it. TheEarthFaultelementoperatedevery timetheloadincreasedbeyondacertain limit (butwithinTRlimit). Asitwasa continuousprocessplant, theyhadturned offtheEarthFaultprotectionandwere runningthefeederwithouttheEarthFault protection. Theywantedtotakethis protectioninline. Findings : AspertheEIC, theplantoperatedonlow loadsandtherewasnoevidentfault (i.e., shortcircuitorconsiderableleakage). Uponchecking, EarthFaultprotectionwas foundtobeofDerivedtype. As, itcanbeseen (Image1) ontherelay, CurrentintheNeutralisaround610A. Earth FaultPick-upwassetat400Aintherelay. Hence, relaykeptoperatingwhenitsensed highercurrent. PhaseCTswerehavinga ratioof4000/1AandtheEarthFault elementwassetat400A, i.e., 10 %. InDerivedtypeEarthFaultprotection, currenttotherelayisfedfromthePhase CTsonly. FromtheavailablePhasecurrents, relaycalculatestheresidualcurrentwhich isrepresentedastheEarthFaultcurrent. Hence, insidetherelay, vectorsummation ofPhasecurrents (Ia, Ib & Ic) iscarriedout andEarthFaultcurrent (In) isderived. Root Cause Analysis Theprogrammingoftherelaywasfoundin order. Trippingrelayswereassignedand operatedasperdrawings. TheRelaywastestedbysecondaryinjection methodandfoundhealthy. Abovevectorsumisalwayszeroinnormal condition. Hence, iftheEarthFaultelement operates, itisunderstoodthatthis summationisnon-zero, thereissome unbalancinginthreephasecurrents, which ishigherthantheadoptedsettings. ThewiringtorelayfromCTandtheCTlinks werefoundalright. Itwasdecidedthento checktheCTsforitsvariouscharacteristics. www.systemprotection.in +91-265-2225137

  3. Usually, forhigherratingCTs, Primary InjectionatSiteisdoneatcomparatively lowercurrents, duetosizeandweight limitationsposedbyhighercurrent - injectionkits. Besides, evenifwesomehow managetoinjectsuchheavycurrents, it doesnotusuallyleadtoconclusiveRatio Measurement. Highcurrentsgenerate considerableheatintheinjectioncables (duetoI2t), whichinturnresultsin fluctuationofcurrents, asthecable resistancekeeponchangingdueto heating. Moreover, measurementofsuch largeprimarycurrentswithClamp-onMeter isalsoachallenge. So, weemployedastate-of-the-artCT TestingInstrument, CTAnalyzerofOmicron Make, whichusesIEC61869-2standardand performsmodel-basedtestingwhichisfar moreaccurateandconclusive. The following are the results of Y Phase CT : CT Analyzer Test Results for Y Phase CT Attimes, routinetestequipments, suchas PrimaryInjectionKit, donotprovidethe conclusiveresults. Itislikelythatthefaultin theequipmentmaygounnoticed / uncheckeddespitecarryingoutRoutine Testing. WefoundthatRandBPhaseCTswere havingminorerrors, butYphaseCThada ratioerrorof50 % atratedburden. It means, CTwillactasitishavingaratioof 4000/0.5Ainsteadof4000/1A. Phaseangle errorwasalsofoundtobe -1574.06min. Upgradingourselvesconstantlywith advancedtechnologyhasalwaysbeenat theforefrontforus, andweinvestheavilyin suchtechnologysothatourCustomerscan keeptheirprotectionsystemssaferand morereliable. Duetohigherrors (MagnitudeandPhase angle) ofYPhaseCT, relaymal-operatedin EarthFaultelement. Transformerisaveryimportantasset, and thelossofproductionduetomal-operation ofitsprotectionsystem, canrunintocrores. Alloureffortsareviewingtheproblems fromcustomers’ pointandresolvingthem intotality. ThefaultyCTwasreplacedwithanewCT afterpropertestingandwiring, the Transformerwasswitchedonandre- commissionedwithloading. Conclusion – how advanced technology can help solve such issues more accurately www.systemprotection.in +91-265-2225137

  4. Theabovewasinfactthemajorproblem found, wealsoobservedsomeminor abnormalitiesandcorrectedthemtoo. Therecouldbemanyreasonsformal- operationofTransformerProtectionSystem andcanbeaddressedoncase-to-casebasis. Toknowmore, youmaycall/writetous. Andifyouarelookingforadedicated agencythatunderstandsthedirectlink betweenyourassetsandyourrevenue, call/writetous, wewillbehappytoassist you. www.systemprotection.in +91-265-2225137

  5. CONTACT INFORMATION 301/2/306, SilverlineComplex,OppositeBBC Tower,Sayajigunj,Vadodara - 390005, Gujarat, India. bdm@systemprotection.in www.systemprotection.in +91-265-2225137

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