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Case Study - How Proactive Electrical Maintenance team saved a Power Transformer

Case Study - How Proactive Electrical Maintenance team saved a Power Transformer. Your valuable 10 minutes may avoid breakdown of Electrical Equipment in your plant.<br>

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Case Study - How Proactive Electrical Maintenance team saved a Power Transformer

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  1. ISO 9001:2015 ISO 45001:2015 (OH & S) Certified Company Case Study How Proactive Electrical Maintenance team saved a Power Transformer www.systemprotection.in +91-265-2225137

  2. Powertransformerofrating 31.5 MVA, 66/11 kV isusedforpowerdistributiontoutilities throughan11kVswitch-gear, theywere havingthreeTransformersofidentical rating, inwhichallthreetransformersarein chargedcondition & thetransformerwhich wearetalkingaboutisusedasastandby transformer. Your valuable 10 minutes may avoid breakdown of Electrical Equipment in your plant Today, wearegoingtopresentacasestudy of ‘POWERTRANSFORMER’, whichwenever heardofforthoughtthatsuchevencase mayhappeninplantsbuthappenedinone. However, wewishtosharetheexperience, sothattheproblemMaintenanceEngineers facedinthatplant, maynotbefacedby othersorcanbeavoided. Thetransformerswereincharged condition, predominantlythe1stand3rd transformerswereinaloadedcondition comparativewiththe2ndone. Almostone yearpassed, allthreetransformerswere functioningnormally, withaloadof10to 20% ofitsratedcapacity. Thiscasestudyshows, howPro-active Engineers, preventiveMaintenance & Routinetestingactivitiescansaveyour ElectricalEquipmentsandRevenueworth crores. www.systemprotection.in +91-265-2225137

  3. Incident of Fault : TheMaintenanceteamdidn’ttakeanyfinal verdictonshuttingdownthetransformer, formoreassurance, theyhavesenttheoil samplestoanotherfourlabsjustfor checkingtheactualincreaseinC2H4by authenticatingwiththeirownlabresults, thesamplesweresenttotwoprivatelabs, onetoOEMandonesampletoERDA, all theresultswerenotthesame, moreover thereisasignificantchangeinC2H4as comparedwithothers. AsayearlyPreventivemaintenanceactivity, theall3transformersmaintenancehas beencarriedout, everythingwasfoundin order, themineraloilsamplesofallthree transformerswerecollectedandhasbeen senttothenearestLabforanalysisofDGA, BDV & watercontent. TheDGAtestresultsofTransformer#2was foundabnormalcomparedwiththepast testresults (firstresultbeforecharging), the C2H4(Ethylene) contentwasfound immense, asperIEEEC57.104standardsit shouldbelessthan50ppm. Butwherehas inthetestresult, thecontentofC2H4was foundaround402ppm, almost8timesthe specifiedlimitasperIEEE. Below is the results of Oil test www.systemprotection.in +91-265-2225137

  4. COMPARISON OF DGA RESULTS WhileconductingInsulationresistancetest thevoltageisnotwithstanding/ buildingup normally, allofasudden, theteamnoticed somechatteringsoundfrominsidethe transformer, alltheteammemberswere inspectingthetransformerfromallthree sidesofinspectionwindow, butthe chatteringsound/ sparkisnotaccurately visible. TheTransformerisde-energized & OEM representativehasbeencalledouttothe plantlocationtofurtherscrutinizethecase, thesiteteamperformedsomeelectrical teststoensurethehealthiness, thetest resultswerefoundinorder. OEMrecommendeddispatchingthe transformertotheirworksforfurther investigation, thetransformerisdispatched fromthesiteandthesiteteamalso reachedtoOEMworksforinspection. Theoilhasbeendrainedoutofthe transformer, themanholecoverswere removed, thecoreyokeandtankshorting pointdisconnected/separated, IRtest conductedbetweentheseparatedpoints (Core & yokeframe) withrespecttoground, avoltageof2500Voltsisappliedtocheck thehealthinessofinsulation. Asthereisacomplicationtoenterinside thetransformerduetothespaceconcern betweenthebodyandthecore-coil assembly, theinspectionwindowinthree sideswasopenedforconductingtheabove test. www.systemprotection.in +91-265-2225137

  5. CCA OF THE SAID TRANSFORMER Thecorehasbeenliftedfromthebodyand visualinspectionperformed, no abnormalitiesfound, Insulationresistance betweencore & yokeframeconducted @ 2500volts, chatteringsoundobserved. Finally, casewasconcluded, onewasher foundrestingonthebottomofacenter limbofcoreandtouchingtheyokeframe resultinginsparking/chattering. Pic of the washer which was resting in the bottom of the center limb. OMG! From where this washer came inside the transformer? Conclusion that can be drawn from this Wecan'tjudgethisnow, however, this washermayhavegoneinsidethe transformerinOEMworkplaceitselforelse insiteduringinstallationofthetransformer, wemaysaythatitwassheernegligenceor poorworkmanship. Butthiscanhappen Incident : Conclusionwhichmaintenanceteamof thatplantcameupwith, whichmaynotbe feasible, butiftheyhavedoneit, theycould havesavedlotoftimeandmoney. AfterremovalofwasherInsulation resistancetestconductedthevalueswere foundmorethan500Mega-ohms. Belowistheconclusiondrawnbythe maintenanceteamofthatplantareas below Thetransformerhasbeenpackedand testinghasbeendone, everythingfound normal, thesamehasbeencommissioned andtakeninservice. www.systemprotection.in +91-265-2225137

  6. Points to be considered before & after commissioning of the Transformer (related to this case study) :- 1.    Afterreceiptofthetransformeratyour premises, don’tforgettocheckthe insulationresistanceofCore & Yokeframes earthingpointindividuallywithrespectto theground/ body. 4.    DGA / Oiltestreportshouldbecross verified (ifthereportisnotwithin prescribedlimits) withaminimumofOne NABLaccreditedlabs, beforeconcluding. 2.    Ifthesepointsarenotavailableoutside thetransformerbody, thenthemanhole covertoberemovedandallthesethree pointstobeisolatedandinsulation resistancetobeconductedasstatedin pointno1. 5.    Whileerectingtransformerandits accessories, oneshouldbeverycautiousof handlingmaterialsandonemustdouble checkthatnothingisfellinsidethe transformertank, beforeboxingup & oil filtration/ charging. 3.    DGAtobecarriedoutbeforecharging, aftercharging (noload24hrs), inaloaded condition (after24hrs) & afteramonth, whereonlineDGAisnotavailable. Hope it will help you, also share this with other Electrical Engineers you know. Any other suggestions are welcomed. www.systemprotection.in +91-265-2225137

  7. 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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