Information Notice 1988-75, Disabling of Diesel Generator Output Circuit Breakers by Anti-Pump Circuitry
IUNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555September 16, 1988NRC INFORMATION NOTICE NO. 88-75: DISABLING OF DIESEL GENERATOR OUTPUTCIRCUIT BREAKERS BY ANTI-PUMP CIRCUITRY
Addressees
- All holders of operating licenses or construction permits for nuclear powerreactors.
Purpose
- This information notice is being provided to alert addressees to potentialproblems where the capability to either automatically or manually closediesel generator circuit breakers from the control room may be lost. Itis expected that recipients will review the information for applicabilityto their facilities and consider actions, as appropriate, to avoid similarproblems. However, suggestions contained in this information notice do notconstitute NRC requirements; therefore, no specific action or written responseis required.
Description of Circumstances
- On June 5, 1988, operators at Browns Ferry Unit 3 were unable to reclose thediesel generator output breakers to the 4-kV shutdown boards from the controlroom during a loss-of-power/loss-of-coolant-accident (LOP/LOCA) test. Duringthe test, the output breakers connected the diesel generators to their respec-tive 4-kV shutdown boards after the LOP signal was generated; however, thebreakers tripped and remained open after receiving the LOCA signal. Operatorsdiagnosed the output breaker lockout problem using system electrical configu-ration drawings. An operator was sent to the 4-kY shutdown board to manuallytransfer output breaker control power to its alternate source. This momentarilyremoved power, enabling the breaker to close when the power was restored.On October 14, 1987, an operator at Wolf Creek Generating Station manuallytripped the output circuit breaker of the emergency diesel generator (EDG)from the control room. At the time, the EDG was supplying a vital bus. Whenthe operators tried to reenergize the vital bus from the still-operating EDG,they found that they could not close the EDG output breaker from the controlroom. The vital bus was finally reenergized from the offsite power supply.Through examination of the breaker control schematics the licensee laterfound that the EDG circuit breaker could be closed by cycling the EDG modeswitch at the EDG local control station.880920197 IN 88-75September 16, 1988 Discussion:The anti-pump circuit configuration will protect large breakers from rapidcycling and, under certain circumstances, will prevent breaker closure. AtBrowns Ferry Unit 3, a unique sequence of events, a LOP signal followed within6 seconds by a LOCA signal, led to the discovery of a design deficiency of thiscircuit configuration. Contacts from the undervoltage relay will seal in thebreaker anti-pump relay until the undervoltage condition on the 4-kV boardsclears.The circuit is designed such that following a LOP, the undervoltage conditionmust exist for at least 5 seconds and the diesel. must reach rated speed beforethe diesel generator output breaker will close on the bus. Once the breakerhas closed, the closure spring recharge motor and the breaker anti-pump relaywill be energized. A fully discharged closure spring requires 2 seconds forthe spring to be fully recharged. During this 2 second window the anti-pumpcoil will remain energized via contacts sensing spring position, and if anundervoltage condition exists on the 4-kY bus it will seal in and lock openthe breaker.During the Browns Ferry event, the EDG output breaker closed 5 seconds afterthe LOP signal, the undervoltage condition was eliminated, and the undervoltagerelay began its 5 second cycle to reset from the undervoltage condition. About1.5 seconds 1ater. the. LOCA-signaL-retr-ipped-the-breaker-and-created-another--undervoltage condition on the 4-kV bus. At this point, because the undervoltagerelay had not completed its reset cycle, the undervoltage relay remained in itsundervoltage state. Therefore, the undervoltage relay sealed in the still-energized anti-pump relay because the undervoltage condition occurred beforethe breaker charging spring was fully charged. Thus, the breaker could notbe closed from the control room either manually or automatically until controlpower was removed, which deenergized the anti-pump relay.The Browns Ferry licensee modified the breaker control logic to prevent the anti-pump relay from sealing in during a LOCA condition by adding a time-delay relayin the breaker trip coil circuitry. This relay will be energized by a LOCAsignal and its contact in the anti-pump coil seal-in path will open after a2-to 5-second delay to prevent anti-pump coil seal-in and breaker lockout.The Wolf Creek EDG output circuit breaker has automatic closing logic to closethe circuit breaker when the following five permissives are satisfied:(1) Both offsite circuit breakers are open'(2 The EDG mode switch is in the automatic mode.(3 Lockout relays are deenergized.(4 A 3-second time delay has elapsed.(5) The EDG has reached operating speed and voltage.This logic sends a constant close signal to the circuit breaker that keeps thebreaker's internal anti-pump relay energized as long as the logic permissivesare satisfied. The anti-pump relay prevents the circuit breaker from cyclingif attempts are made to hold the breaker closed against a valid trip signal.I',
IN 88-75September 16, 1988 When the Wolf Creek operator manually tripped the EDG output breaker, the auto-matic closing logic permissives remained satisfied. Therefore, the anti-pumprelay remained energized, preventing reclosure of the circuit breaker. Cyclingthe EDG mode control switch at the local control station allowed the circuitbreaker to reclose by momentarily interrupting the automatic close signal, there-by resetting the anti-pump logic. When the mode switch contact was reclosed byreturning the switch to the "auto' position, the circuit breaker's automaticclosing logic closed the breaker.The Wolf Creek licensee modified the EDG breaker control switch located in thecontrol room to enable the operator to reclose the EDG circuit breaker from thecontrol room. This switch was originally intended only as a means of parallelingthe EDG with the offsite power supply. With the current modification, the switchcan be used to reset the anti-pump logic and allow the automatic circuit to re-close the breaker. The modification added a contact that is closed in the "normal"position and open in the "trip" and "pull to lock" positions of the control switch.When operators manually trip the EDG circuit breaker from this control switch,the contacts open to interrupt the close circuit and reset the circuit breakeranti-pump relay. If the operator wishes to keep the breaker open, he must putthe switch in the "pull to lock" position. Returning the switch to the "normal"position completes the automatic close circuit and the breaker recloses.It should be noted that although the above discussion has dealt only with EDGoutput- circuit breakers, anti-pump circuit problems could also apply to otherbreakers that use automatic closing logic, such as load-sequencing breakersand offsite supply breakers to the emergency buses.The information herein is being provided as an early notification of a potentiallysignificant matter that is still under consideration by the NRC staff. If NRCevaluation so indicates, specific licensee actions may be requested.No specific action or written response is required by this information notice.If you have any questions about this matter, please contact one of the technicalcontacts listed below or the Regional Administrator of the appropriate regionaloffice.Di rectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: James Lazevnick, NRR(301) 492-0814Carl Schulten, NRR(301) 492-1192Fred Burrows, NRR(301) 492-0783Attachment:List of Recently Issued NRC Information Notices
Att"aantIN 88-75September 16, 1988Page I of ILIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESNotice No. Subject Issuance88-74 Potentially Inadequate 9/14/88Perfornance of ECCS inPWRs During RecirculationOperation Following a LOCA88-73 Direction-Dependent Leak 9/8/88Characteristics ofContainment Purge Valves88-72 Inadequacies in the Design 9/2/88of dc Motor-Operated Valves88-71 Possible Environmental 9/1/88Effect of the Reentryof COSMOS 1900 andRequest for Collectionof Licensee RadioactivityMeasurements Attributedto That Event88-70 Check Valve Inservice 8/29/88Testing ProgramDeficiencies88-69 Movable Contact Finger 8/19/88Binding in HFA RelaysManufactured by GeneralElectric (GE)88-48, Licensee Report of Defective 8/24/88Supplement I Refurbished Valves88-68 Setpoint Testing of Pres- 8/22/88surizer Safety Valves withFilled Loop Seals UsingHydraulic Assist Devices88P67- -P-F Zfiiairy Fiedeaer Pump 8/Z2j88Turbine Overspeed TripFailureOL
- Operating LicenseCP
- Construction PermitIssued toAll holders of OLsor CPs for W and8&W-designei nuclearpower reactors.All holders of 0Lsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors, fuelcycle licensees,and Priority Imaterial licensees.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors.All holders of OLsor CPs for nuclearpower reactors._UNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D.C. 20555OFFICIAL BUSINESSPENALTY FOR PRIVATE USE, $300FIRST CLASS MAILPOSTAGE & FEES PAIDUSNRCPERMIT No. 0-57 IN 88-75September 16, 1988 When the Wolf Creek operator manually tripped the EDG output breaker, the auto-matic closing logic permissives remained satisfied. Therefore, the anti-pumprelay remained energized, preventing reclosure of the circuit breaker. Cyclingthe EDG mode control switch at the local control station allowed the circuitbreaker to reclose by momentarily interrupting the automatic close signal, there-by resetting the anti-pump logic. When the mode switch contact was reclosed byreturning the switch to the "auto" position, the circuit breaker's automaticclosing logic closed the breaker.The Wolf Creek licensee modified the EDG breaker control switch located in thecontrol room to enable the operator to reclose the EDG circuit breaker from thecontrol room. This switch was originally intended only as a means of parallelingthe EDG with the offsite power supply. With the current modification, the switchcan be used to reset the anti-pump logic and allow the automatic circuit to re-close the breaker. The modification added a contact that is closed in the "normal"position and open in the "trip" and "pull to lock" positions of the control switch.When operators manually trip the EDG circuit breaker from this control switch,the contacts open to interrupt the close circuit and reset the circuit breakeranti-pump relay. If the operator wishes to keep the breaker open, he must putthe switch in the "pull to lock" position. Returning the switch to the "normal"position completes the automatic close circuit and the breaker recloses.It should be noted that although the above discussion has dealt only with EDGoutput circuit breakers, anti-pump circuit problems could also apply to otherbreakers that use automatic closing logic, such as load-sequencing breakersand offsite supply breakers to the emergency buses.The information herein is being provided as an early notification of a potentiallysignificant matter that is still under consideration by the NRC staff. If NRCevaluation so indicates, specific licensee actions may be requested.No specific action or written response is required by this information notice.If you have any questions about this matter, please contact one of the technicalcontacts listed below or the Regional Administrator of the appropriate regionaloffice.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: James Lazevnick, NRR(301) 492-0814Carl Schulten, NRR(301) 492-1192Fred Burrows, NRR(301) 492-0783Attachment: List of Recently Issued NRC Information Notices*SEE PREVIOUS PAGE FOR CONCURRENCEOFC *OEAB *Tech Ed *SL:OEAB *C:OEAB *D:DEST *C:OGCBNAME CSchulten BCalure PBaranowsky WLanning LShao CBerlinger e lDATE 9/7/88 7/28/88 9/7/88 9/7/88 8/24/88 9/8/88 9/(,f 88 IN 88-September , 1988 contact was reclosed by returning the switch to the "auto" position. thecircuit breaker's automatic closing logic closed the breaker.The Wolf Creek licensee modified the EDG breaker control switch located in thecontrol room to enable the operator to reclose the EDG circuit breaker fromthe control room. This switch was originally intended only as a means ofparalleling the EDG with the offsite power supply. With the currentmodification. the switch can be used to reset the anti-pump logic and allowthe automatic circuit to reclose the breaker. The modification added acontact that is closed in the "normal" position and open in the "trip" and"pull to lock" positions of the control switch. When operators manually tripthe EDG circuit breaker from this control switch. the contacts open tointerrupt the close circuit and reset the circuit breaker anti-pump relay.If the operator wishes to keep the breaker open. he must put the switch in the"pull to lock" position. Returning the switch to the "normal" positioncompletes the automatic close circuit and the breaker recloses.It should be noted that although the above discussion has dealt only with EDGoutput circuit breakers. the anti-pump circuit problem could also apply to otherbreakers that use automatic closing logic, such as load-sequencing breakers andoffsite supply breakers to the emergency buses.The information herein is being provided as an early notification of apotentially significant matter that is still under consideration by the NRCstaff. If NRC evaluation so indicates. specific licensee actions may berequested.No specific action or written response is required by this informationnotice. If you have any questions about this matter, please contact any of thetechnical contacts listed below or the Regional Administrator of the appropriateregional office.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical Contacts: James Lazevnick. NRR(301) 492-0814Carl Schulten. NRR(301) 492-1192Fred Burrows. NRR(301) 492-0783-e --- --:D: -NAME :CSchu Mn are :P aranowsky :WLan n :LShao :CBeri nger :ERossiDATE q 88 /8 :1/88 /88 :18188 /88OFFICIAL RECORD COPY
IN 88-August .1988 contact was reclosed by returning the switch to the "auto" position. thecircuit breaker's automatic closing logic closed the breaker.The Wolf Creek licensee modified the EDG breaker control switch located in thecontrol room to enable the operator to reclose the EDG circuit breaker fromthe control room. This switch was originally intended only as a means ofparalleling the EDG with the offsite power supply. With the currentmodification. the switch can be used to reset the anti-pumping logic and allowthe automatic circuit to reclose the breaker. The modification added acontact that is closed in the "normal" position and open in the "trip" and"pull to lock" positions of the control switch. When operators manually tripthe EDG circuit breaker from this control switch, the contacts open tointerrupt the close circuit and reset the circuit breaker anti-pumping relay.If the operator wishes to keep the breaker open. he must put the switch in the"pull to lock" position. Returning the switch to the "normal" positioncompletes the automatic close circuit and the breaker recloses.It should be noted that although the above discussion has dealt only with EDGoutput circuit breakers, the same problem could also apply to other breakersthat use automatic closing logic, such as load-sequencing breakers and offsitesupply breakers to the emergency buses.The information herein is being provided as an early notification of apotentially significant matter that is still under consideration by the NRCstaff. If NRC evaluation so indicates. specific licensee actions may berequested.No specific action or written responses is required by this informationnotice. If you have any questions about this matter, please contact either thetechnical contacts listed below or the Regional Administrator of the appropriateregional office.Charles E. Rossi. DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor Regulation
Technical Contact:
James Lazevnick. NRR(301) 492-0814Carl Schulten. NRR(301) 492-1192Fred Burrows. NRR(301) 492-0783OFC _: T EOGCB :D:DOEAt "4i> -:-8{tjA---:-4og-yF---:---4----------------- :-----------NAME :CSchulten :B& lure :PB pnowsky :WLanni:LS :CBerlinger :ERossiDATE 1&/ : //88 F./ A1/88 1.V1.88 4f8 8 8DAT O F:I g/ECORD : / /88COPYOFFICIAL RECORD COPY
NRC INFO NOTICE 88-XX. DIESEL GENERATOR CIRCUIT BREAKERS FAIL TO AUTOMATICALLYCLOSEOFC :OEAB :Te h Ed :SL:OEAB :C:OEAb :L:SELB :C:OGCB :D:DUEANAME :CSchulten lure :PBaranowsky :WLanning :FRosa :CBerlinger :ERosslDATE : / 88 /88 : I /88 / /88 : / /88 : / /88OFFICIAL RECORD COPY