Class1EProtection(UnbalancedVoltageRelays)

NRCPublicMeetingDecember7‐8,2016

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Preston Cooper, TVA EngineeringTamatha Womack, TVA Engineering

ProtectthefunctionalityofClass1Eequipmentfromunbalancedvoltage,includingthepresenceofanopen

phaseofconsequence.

Class1EUnbalancedVoltageProtectiveFunctionClass1EUnbalancedVoltageProtectiveFunction

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OpenPhasevs.UnbalancedVoltageOpenPhasevs.UnbalancedVoltage

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• Anopenphaseeventcausesvoltageirregularities• Unbalancedvoltagesarealsocausedbyothereventsincludingbreakerfailures,gridunbalance,auxiliarysystemunbalance,etc.

• Voltageisadirectmeasurableparameterwhichcandeterminetheabilityofequipment tofunction.

OffsitePowerConnectionsSequoyahNuclearPlant(SQN)

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SimplifiedOffsitePower(OSP)ConnectionsSimplifiedOffsitePower(OSP)Connections

OffsitePower OffsitePowerCircuit#1 Circuit#2

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TheClass1EsystemisimmediatelyconnectedtooneGDC17offsitepowersource(i.e.,notransferrequired)duringallmodesofoperation.

Including:• NormalOperation• UnitTrip/FullLoadRejection• DesignBasisAccident• UnitStartUp• UnitShutdown/Refuel

OffsitePowerConnectionDescriptionOffsitePowerConnectionDescription

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TVAUnbalanceVoltageRelayDesignBasis

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• Voltageunbalancecancauseseriousmotoroverheatingdamageduetonegativesequencecurrent(I2).

• NEMAMG‐1:– Motorscanwithstand1%voltageunbalance,shouldnotbeoperated

with>5%voltageunbalance– Above1%voltage,themotormustbede‐ratedduetoexcessheating

• Wellknowninverse‐timerelationshipbetweenvoltageunbalanceandmotorthermaldamage1

TVAUnbalanceVoltageRelayDesignBasisTVAUnbalanceVoltageRelayDesignBasis

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1. Motor Temperature Estimation Incorporating Dynamic Rotor Impedance, IEEE Transactions on Energy Conversion, Vol. 6, No. 1, March 1991

• Provide100%protectionagainstlossofsafetyfunctionduetounbalancedvoltagesatthesafety‐buses,includingupstreamopenphaseevents– Includingbothin‐plantandtransformeropenphaseevents

• Utilizeexistingundervoltageprotectioncircuits– Existingsensingcircuits(BusPTs)– Existinglogiccircuits(tripoffsitepower)– Minimalmodificationcosts

• UtilizerelaysqualifiedforClass1Euse– TVAchoosingABBType60QPhaseUnbalanceRelay

(negativesequenceovervoltage)duetoexperiencewithsimilarrelays

• Utilizebottom‐upsetpointmethodology

TVAUnbalanceVoltageRelayDesignBasisTVAUnbalanceVoltageRelayDesignBasis

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UnbalanceVoltageRelaySetpointMethodologyUnbalanceVoltageRelaySetpointMethodology

“LOSSOFLIFE”Protectsagainstlongtermmotordegradation:• SetpointbasedonANSIallowablevalues

• Timedelayallowsforclearinganticipatedgroundfaults

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UnbalanceVoltageRelaySetpointMethodologyUnbalanceVoltageRelaySetpointMethodology

“EVERYTHINGWORKS”Protectsagainstlossofsafetyfunctiononoffsitepower:• Nomotorstriponcurrent

(runningorstarting)• Nomotorstartfailure,

includingLOCAsequencing• Timedelaybasedonsafety

analysislimitforEDGstarttime

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UnbalanceVoltageRelaySetpointMethodologyUnbalanceVoltageRelaySetpointMethodology

“SURVIVE”Protectsabilitytosurvivetheunbalanceandtransferrequiredsafetyloadstoonsitesupply:• Nomotorstriponcurrent

(runningorstarting)• Timedelaybasedonsurvival

time@100%unbalance

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UnbalanceVoltageRelaysAddedtoExistingUndervoltageCircuits

UnbalanceVoltageRelaysAddedtoExistingUndervoltageCircuits

Voltage UnbalanceRelays (Type 60)

Undervoltage Relays(Type 27)

Trip

Permissive 1/2 Logic

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*SetpointsareTechSpecvalues

**ActivationofMCRindicationandtripfunctionrequireLARapproval

UnbalancedVoltageRelaySchemeUnbalancedVoltageRelayScheme

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UnbalanceVoltageRelays(ABB60Q):AlreadyQualifiedforClass1EUse

UnbalanceVoltageRelays(ABB60Q):AlreadyQualifiedforClass1EUse

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TVA’sUnbalanceVoltageRelaySetpoints

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UnbalanceVoltageRelaySetpointMethodology

UnbalanceVoltageRelaySetpointMethodology

Affect on Function Response Required

Red Limited allowable time since loss of function is imminent due to protective device actuation.

Automatic Response (< allowable manual action time)

Yellow Limited allowable time since heating may outpace protective relays. This will result in loss of equipment life.

Controlled Response (loss of life is gradual and equipment is functional)

Green Unlimited allowable time. No affect on equipment function. No response required (full capacity and capability)

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SQNAnalyticalLimitsSQNAnalyticalLimits

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Relay

Voltage(Volts Line-Neutral Secondary)

Time Delay(Seconds)

Lower Limit Upper Limit Lower Limit Upper Limit

Alarm 0.9 *1.5 0.3 *3.0

Low Trip 1.5 *3.3 4.0 *10

High Trip 3.3 *20.0 3.0 *4.0

*designatedanalyticallimits

• Toavoidnuisanceactuations,thethreerelays’nominalpick‐upsettingsshouldbeascloseaspossibletotheupperlimits,accountingforassociatederrorsandtolerances.

• ThetimedelaysetpointsfortheLowTripandtheHighTriprelaysmustnotoverlapwiththeAlarmrelaytimedelaysetpoint,accountingforassociatederrorsandtolerances

Class1ECompliancewithNRC’s4FunctionalRequirements

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• Class1Equalifiedprotectiverelays(ABB60Q)oneachtrain/division

• Permissive1outof2logicschemetoprovidereliability

• AnyfailureofacomponentistheClass1Efailureandthesecondtrainwillremainavailable,persinglefailurecriteria.

FunctionalRequirement1–SingleFailureFunctionalRequirement1–SingleFailure

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• AutomaticdetectionandMCRalarmoccursforallopenphaseeventsthatadverselyeffectconnectedsafetyloads– Automaticdetectionisavailableimmediatelyupon

connectiontoastandbyoffsitepowersource• Foropenphaseeventsthatdonotadverselyeffectconnectedsafetyloads,thestationwillremainontheadequateandcapableGDC‐17source.– OPCsonstandbysourcescanbedetectedinmeansother

thanautomatic• VisualinspectionscanoccurwithinallowableLCOtimeandstillmeettheintentoftheTechSpecsforoperabilityofoffsitepowersource.

• Consistentwithexistingdegradedvoltage/lossofvoltageprotectionschemes.

FunctionalRequirement2–AutomaticDetectionofOPCFunctionalRequirement2–AutomaticDetectionofOPC

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Consistentwithdegraded/lossofvoltageprotection• SetpointsensureClass1Eequipmentwillbeabletoprovidetheirsafetyfunctionunderallanticipatedoperationaloccurrences,includingaconcurrentdesignbasisevent.

• Timedelaysensurethepowersourceisautomaticallytransferredtotheonsitepowersystemwithinthetimeassumedintheaccidentanalysis.

FunctionalRequirement3–TimeDelayFunctionalRequirement3–TimeDelay

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UnbalancedVoltageTSLCOandSurveillanceRequirementswillbeconsistentwithexistingundervoltage(i.e.,DVR)• LossofPowerDieselGeneratorStartInstrumentation(TS3.3.5)isbeingmodified

• Newfunctionprovidedbytheunbalancedvoltagerelaysforinitiationofthedieselgenerators

FunctionalRequirement4–TechSpecsFunctionalRequirement4–TechSpecs

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Summary

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•UnbalancedvoltagemethodologyhasbeenvalidatedthroughfieldtestingatBellefonteNuclearPlant.•AllunbalancedvoltagerelayshavebeeninstalledatSQNwithouttripenabled.•Monitoringsetpointaresetsignificantlylowerandinsuchamannertoprovidegranularity.

SummarySummary

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• Relayshaveappropriatelyrespondedtoinplantandgridevents(e.g.,lighteningstrike,relaytesting,griddisturbance,boardtransfer,maingeneratorpowerchanges,etc.)

• Noeventhasoccurredthatwouldchallengethefinalsetpointsonceimplimented (i.e.,resultinatrip)

TVAFleetMonitoringSummaryTVAFleetMonitoringSummary

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Questions

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