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Presentation - Transformer Failure Due to Breaker Switching Transients

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Presentation - Transformer Failure Due to Breaker Switching Transients
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  1 Transformer Failure Due to Circuit Breaker Induced Switching Transients David D. Shipp, PEFellow, IEEEEaton Electrical Group130 Commonwealth Dr.Warrendale, PA 15086 Thomas J. Dionise, PESenior Member, IEEEEaton Electrical Group130 Commonwealth Dr.Warrendale, PA 15086 Visuth LorchEaton Electrical Group130 Commonwealth Dr.Warrendale, PA 15086 IEEE Central Tennessee SectionMay 1, 2012 2 2 Central Tennessee SectionMay 1, 2012 Introduction ãSwitching transients associated with circuit breakers observed for many yearsãBreaking opening/closing interacts with the circuit elements producing a transientãThe severity of the transient is magnified by breaker characteristics ãCurrent chopping on openingãPre-strike or re-ignition on closing ãIn limited instances, the transient overvoltage exceeds transformer BIL resulting in failureãRC snubber in combination with surge arrester mitigates the transient  2 3 3 Central Tennessee SectionMay 1, 2012 Introduction -Outline ãForensic evidence and history of failuresãUnderlying conceptsãPredicting performance with simulationsãMitigating the transients with snubbersãConcerns for data centers & overall industryãCustom designing the snubber ãSnubber performance measurementsãOther considerations 4 4 Central Tennessee SectionMay 1, 2012 Data Center NJ –Forensic Evidence ãFour electricians “simultaneously” opened four 26kV VCBsãsimulate utility outageãsystems transferred to standby generationã“loud pop” in Sub Rm B ãthe relay for VCB feeding transformer TB3 signaled tripãMinutes later, two electricians “simultaneously” closed two 26kV VCBsãbreakers to Sub Rm Aãtransformer TA3 failed catastrophically  3 5 5 Central Tennessee SectionMay 1, 2012 Transformer Failure #2 -Energization ãExamination of primary windings ãCoil-to-coil tap burn off ãWinding showed an upward twistãBurn marks from the initial blastãTransient on first turns of windings 6 6 Central Tennessee SectionMay 1, 2012 Transformer Failure #1 –De-energization ãExamination of primary windings ãFlash and burn marks on b-phase at bottom & middleãBottom -Indicate a coil-to-coil flashover (high dv/dt)ãMiddle –cable used to make delta swung free (lack of support)ãTransformer passed BIL test at 150kV but failed at 162kVBoth failed units:ã40 feet of cableãHigh efficiency designãVCB switching  4 7 7 Central Tennessee SectionMay 1, 2012 History of Failures –Forensic Review CaseFacilityVoltageCable FeetBilType Arrester Failure ModeVendorSwitching1*Hydro Dam13.802050DryNo1st turnAClose2Hospital13.802795DryNo1st turnAClose3Railroad26.4037150LiquidN/AmiddleAOpen4Data Center26.4040150Cast coilYes1st turnBClose/Open80150Cast coilYesNoneBClose5Oil Field33.007DryNo1st turnCClose6**Oil Drill Ship11.00<3075Cast coilYes1st turnCCloseNotes: * = 40-50yrs. old with new breaker. ** = 2 yrs. old. All others new.*** = All transformers unloaded or lightly loaded when switched.CircuitVacuum Breaker Transformer*** 8 8 Central Tennessee SectionMay 1, 2012 Common Parameters “Rules of Thumb” to screen applications:ãGenerally, short distance between circuit breaker and transformer ãabout 200 feet or less ãDry-type transformer ãoil filled and cast coil not immune and low BIL ãInductive load being switched ãtransformer, motor, etc. (light load or no load) ãCircuit breaker switching characteristics: ãchop (vacuum or SF6) or restrike (vacuum)
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