ML17286A987

LER 91-017-00:on 910708,ground Fault Occurred in off-site 500 Kv Sys.Caused by Substation Personnel Error & Substation Equipment Design Deficiency.Plant Operators Returned Unit to Startup Power source.W/910807 Ltr

ML17286A987
Person / Time
Site:	Columbia
Issue date:	08/07/1991
From:	John Baker, Reis M WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GO2-91-47, LER-91-017, LER-91-17, NUDOCS 9108140351
Download: ML17286A987 (8)

Text

DISTRIBUTION DEMONSTRATION SYSTEM

~ ~

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSXON NBR:9108140351 DOC.DATE: 91/08/07 NOTARIZED: NO DOCKET N FACIL:50-397 WPPSS Nuclear Project, Unit 2, Washington Public Powe =05000397 AUTH. NAME , AUTHOR AFFILIATXON REIS,M.P. Washington Public Power Supply System BAKER,J.W. Washington Public Power Supply System RECIP.NAME RECIPIENT AFFILIATXON R

SUBJECT:

LER 91-017-00:on 910708,ground fault occurred in off-site 500 kV sys.Caused by substation personnel error & substation equipment design deficiency. Plant operators returned unit D power source.W/910807 ltr. to'tartup DISTRIBUTION-CODE: XE22T COPIES RECEIVED:LTR ENCL SIZE:

TXTLE: 50.73/50.9 Licensee Event Report (LER), Xnciden Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT COPIES D ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1 1 PD5 PD 1 1 ENG,P.L. 1 1 D INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 *1 AEOD/ROAB/DS P 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFB10 1, 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB1 1 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB8H3 1 1 NRR/D~ST SPXB8 Dl 1 1 NRR/DST/SRXB 8E RES/DSIR/EIB 1

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NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOIiI Pl-37 (EXT. 20079) TO ELlivIINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 33 ENCL 33

~ 4i WASHINGTON PUBLIC POWER SUPPLY SYSTEM P.O. Box 968 ~ 3000 George Washington Way ~ Richland, Washington 99352 G02-91-147 NCR No. 291-574 Docket No. 50-397 August 7, 1991 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

NUCLEAR PLANT NO. 2 LICENSEE EVENT REPORT NO.91-017

Dear Sir:

Transmitted herewith is Licensee Event Report No.91-017 for the WNP-2 Plant.

This report is submitted in response to the report requirements of 10CFR50.73 and discusses the items of reportability, corrective action taken, and action taken to preclude recurrence.

Very truly yours, J.W. Baker (N/D 927N)

WNP-2 Plant Manager JWB:ac

Enclosure:

Licensee Event Report No.91-017 cc: Mr. John B. Hartin, NRC Region V Nr. C. Sorensen, NRC Resident Inspector (M/0 901A)

INPO Records Center Atlanta, GA Ms. Dottie Sherman, ANI Nr. D. L. Williams, BPA (N/D 399)

NRC Resident Inspector walk over copy

N RC, FORM 366 U.S. NUCLEAR REGULATOIIYCOMMISSION APPROVED 0MB NO. 31504)104 (669)

EXPIAESs 4/30/92 IMATED BURDEN PER RESPONSE TO COMPLY WTH THIS FOAMATION COLLECTION REQUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LER) COMMENTS REGAADING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (F630), U.S. NUCLEAR AEGULATORY COMMISSION, WASHINGTON. DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31500104), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC20503.

DOCKET NUMBER (2) PA E FACILITY NAME (ll Washin ton Nuclear Plant- - Unit 2 0 5 0 0 0 3 7 s or-()

'""'"'AUTO START OF EMERGENCY'IESEL GENERATORS WHILE ON BACKFEED. UNDERVOLTAGE WAS INITIATED BY A 500KV GRID DISTURBANCE. ROOT CAUSES ARE PERSONNEL, ERROR AND E UIPMENT DESIGN EVENT DATE (5) LEA NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (EI SEOVENTSAL i+@ OAY YEAR FACILITYNAMES DOCKET NUMBER)3)

MONTH DAY YEAR YEAR NUMBER 'NC. NUMBER MONTH 0 5 0 0 0 0 708 91 9 1 01 7 00 08 079 1 0 5 0 0 0 OPERATING THIS REPORT IS SUBMITTED PURSUANT T 0 THE RLOUIREMENTS OF 10 CFR (): ICiseck one or morc of the followinp/ lll MODE (9) 20.402 (5 I 20.405(c) 60,73(el(2)(iv) 73.71(S) 20AOSI ~ )(ll(l) 50.36(c)(1 I 60,73(e) (2)(v) 73.71(cl POWE R LEYEL OTHER ISpecsfy sn Aostrect 0 0 0 20.405(e)ll)(S) 60.36(c)(2) 60.73(eH2)(vB)

Ocrow ensf /n Tert, HIIC Fornv nrN~>>cpps st N 20.405( ~ )ll)liill 50.73(e) (2) (I) 50,73( ~ )(2)(vEI)IAI 366A/

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MANUFAC. REPORTABLE MANUFAC. EPORTABLE '..

CAUSE SYSTEM COMPONENT CAUSE SYSTEM COMPONENT TURER TO NPADS TURER TO NPRDS jrSEIQ+c+ys'.

SUPPLEMENTAL REPORT EXPECTED (14) MONTH DAY YEAR EXPECTED SUBMISSION DATE (15I YES /lf yes. con piete EXPECTED SIISMISSIOH DATE/ X NO ABSTRACT /Limit to Ic(IO sprees i.c., epprorlmetcly fitteen sinple tpece typewritten lines/ (16)

On July 8, 1991 at 0113 hours0.00131 days <br />0.0314 hours <br />1.868386e-4 weeks <br />4.29965e-5 months <br />, Operations personnel responded to the automatic start of the Division 1 and 2 Emergency Diesel Generators. The Diesels started due to undervoltage conditions on their respective vital power buses. The undervoltage condition resulted when a ground fault occurred in the off-site 50OKV system.

Misalignment of protective relay selector switches at a Bonneville Power Administration (BPA) substation precluded primary protective relays from immediately isolating the faulted line. Backup relaying acting to isolate the fault also the WNP-2 backfeed power source and plant buses. Transfer to the 'e-energized Startup power source did not occur since the transfer logic was not satisfied.

WNP-2 undervoltage relays acted to transfer critical bus power to the Backup transformer.

Operations personnel restored station power to the Startup source at 0136 and reestablished Shutdown Cooling at 0156.

The root causes are personnel error on the part of substation operations personnel and substation equipment design deficiencies. Substation personnel are not WNP-2 employees. Personnel and hardware related corrective actions are being pursued by substation management. WNP-2 will monitor the completion of BPA corrective actions. Further, WNP-2 will perform engineering review to confirm existing relaying is sufficient to protect the unit if a similar event had occurred while at power.

NRC Fotm 365(689)

NRC FORM 366A U.S, NUCLEAR REGULATORY COMMISSION

!649) APPROVED OMB NO. 31500106 EXPIRES: B/30/92 ATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE E REPORT (LER) RMATION COLLECTION REQUEST: 60gl HRS. FORWARD MMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENTBRANCH (P430), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31SOOIOS), OFFICE OF MANAGEMENTAND BUDGET,WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2I LFR NUMBER (6) PAGE (3)

M':'EQUENTIAL NUMBER

>'O+

~NO REVISION NUMBER Washin ton Nuclear Plant - Unit 2 0 5 0 0 0 3 7 017 0 0 0 2oFO 6 TEXT /I/moro s/ross is rorlr//rod. Irso odd B'orro/ HRC Fonrr 366A's/ (17)

Plant Conditions Power Level -0 X Plant Mode - 4 - Cold Shutdown Event Descri tion On July 8, 1991 at 0113 hours0.00131 days <br />0.0314 hours <br />1.868386e-4 weeks <br />4.29965e-5 months <br />, Operations personnel responded to an automatic start of the Division and 2 Emergency Diesel Generators.

1 The Diesels started due to undervoltage conditions on their respective vital power buses. The undervoltage was caused by a disturbance in the off-site 500KV system which resulted in total de-energization of the 500KV portion of the Bonneville Power Administration (BPA)

Ashe substation from which the plant was backfeeding.

The disturbance was a ground fault on the Marion line feeding the substation. (See Figure 1 for schematic drawing of Ashe substation. The numbers in circles indicate the opening sequence for the substation breakers.) Misalignment of two protective relay selector switches at the substation precluded the BPA primary relays from immediately isolating the faulted line. The switches allowed breaker 4937 to open but not breaker 4940. Backup relaying (line relays) isolated the Hanford line (by opening breakers 4898 and 4901) and then the Slatt line (via breakers 4888 and 4891). Finally the fault was cleared when a neutral overcurrent relay timed out and opened breaker 4940. The fault was completely isolated in less than-one second.

WNP-2 backfeed de-energized when the Slatt line isolated by opening breakers 4891 and 4888. Since the Hanford, Slatt and Marion line relays are not designed to trip breaker 4885, WNP-2 was left connected to the de-energized South bus through 4885.

Breaker 4885 was not required to open to isolate the fault and did not open.

However, for automatic transfer of station power from the 500KV backfeed configuration to the 230KV Startup transformer (TRS) to function, both 4885 and 4888 must open. As a result, auto-transfer to the Startup source did not occur. The resultant loss of power to critical plant buses was detected by undervoltage protective relays. The loss of voltage relay scheme then transferred Division 1 and 2 critical bus power to the Backup transformer (TRB) within four seconds.

Concurrently, the loss of voltage relays started the Division 1 and 2 Diesel Generators. The High Pressure Core Spray Diesel Generator was out of service for maintenance at the time of the event.

Since transfer to TRB was successful, the diesels did not pick up load. The operating Shutdown Cooling pump,'HR-P-1A, tripped as part of the load shed sequence associated with transfer to TRB.

Immediate Corrective Actions WNP-2 plant operators returned the unit to the Startup power source by 0136 hours0.00157 days <br />0.0378 hours <br />2.248677e-4 weeks <br />5.1748e-5 months <br />, restored Shutdown Cooling by 0156 hours0.00181 days <br />0.0433 hours <br />2.579365e-4 weeks <br />5.9358e-5 months <br /> and secured the Diesel Generators by 0149 hours0.00172 days <br />0.0414 hours <br />2.463624e-4 weeks <br />5.66945e-5 months <br />.

NRC Form 366A (6J)9)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (649) APPROVED 0MB NO. 31500104 LICENSEE E

TEXT COhfTINUATION REPORT (LER)

EXPIRES.'E/30/92 MATED BURDEN PER RESPONSE TO COMPLY WTH THIS RMATION COLLECTION REQUEST: 50/) HRS. FORWARD MMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENTBRANCH IP430), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31500104), OFFICE OF MANAGEMENTAND BUDGET. WASHINGTON, OC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR m SEQUENTIAL REVISION NUMBER NUMSEA Washington Nuclear Plant - Unit 2 O S 0 0 O 017 0 0 0 3 OF 0 6 TEXT /llnxvo E/Nco /J ngoirod, IIJo oddlooIN/HRC Form 36649/ (17)

Further Evaluation and Corrective Action A. Further Evaluation Start of the Diesel Generators due to undervoltage is not considered to be an Engineered Safeguards Feature actuation, according to the WNP-2 FSAR.

Therefore, this LER is voluntarily'ubmitted. Nevertheless the NRC was notified of this event, via ENS, within the four hours allowed by 10CFR50.72(b)(2)(ii). The WNP-2 Resident NRC Inspector was also notified.

The High Pressure Core Spray (HPCS) Diesel Generator was out of service for maintenance during this event. The HPCS system is not designed to transfer to the Backup transformer upon loss of bus voltage. If the Startup transformer is .

not available, the HPCS diesel is the only other source of power to the system. Hence HPCS was unavailable during the event. However HPCS was not being relied upon to satisfy any ECCS requirements.

The Root Causes of this event are personnel error on the part of substation operations personnel and equipment design deficiency. These root causes are confirmed by both substation operator (BPA) and Supply System investigations.

It i s believed the selector switches remained misaligned after planned breaker work. Substation personnel failed to use procedurally prescribed methods for changing component status and logging such actions. Since the relay selector switches had been out of service for approximately 19 days, the BPA investigation specifically addressed their procedural controls over substation activities and log keeping. The controls were found to be satisfactory.

Equipment design is less than adequate since there was no indication in the substation control room that the switches were out of its normal position.

Further there were no features of the switch which would obviously indicate, locally, that it was out of position.

The transfer to TRB involves both the four second time delay and load shedding. The time delay is sufficient to cause a start of emergency diesel generators due to critical bus undervoltage. The start is precautionary and allows to diesels to more rapidly connect to the critical bus in the event that the Backup power is not available.

Load shedding ensures that the inrush current does not exceed transformer ratings when the transformer is initially energized. In thi.s event, Residual

, Heat Removal loop A, which was supplying shutdown cooling, tripped as part of the load shed sequence.

No isolation or scram occurred since the RPS flywheel inertia maintained RPS power until the critical buses were re-energized from TRB.

NRC FomI 366A (649)

NRC FORM 358A U.S. NUCLEAR REGULATORY COMMISSION APPROVEO 0MB NO. 3(50010h(

(tjd9) ~

EXPIRES: O/30/92 ATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE E REPORT (LER) RMATION COLLECTION REQUEST: 50A) HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P430), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO 1HE PAPERWORK REDUCTION PROJECT (315001(M), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (5) PAGE (3)

YEAR SEOVENTIAI. hr'g r(EVrSION Qm NVMSER '~F NVM Err Washington Nuclear Plant - Unit 2 0 5 0 0 0 3 7 9 1 1 7 0 0 4 OF 0 6 TEXT illmore el>>ce /e reh)rhired, o>> edChdorhe/ HAC Form 3(hSA 3/ (IT)

B. Further Corrective Action Corrective action for BPA personnel performance issues are not within the control of the Supply System. However BPA is applying corrective measures to ensure the problem does not recur.

BPA will implement modifications to 1) automatically record relay selector switch activity; 2) annunciate and alert the substation operator if a relay selector switch are out of its normal position; and color coding the selector switches to facilitate visual determination of their position.

Supply System Engineering will review the existing WNP-2 electrical protection relaying scheme to ensure adequate protection of unit equipment if a similar event were to occur during operation. Any significant adverse findings will be reported in a supplemental LER.

Safet Si nificance There is no safety significance. to this event. The unit was already in the cold shutdown mode. Shutdown cooling was lost for 43 minutes, resulting in only a two degree rise in reactor coolant temperature. WNP-2 Technical Specifications allows Shutdown Cooling to be out of service for up to two hours in any eight hour period.

There was no threat to the health and safety of the public or plant personnel.

Had the unit been operating when this event transpired, it is most likely that plant response would have been similar to that experienced. Generator protective relaying would probably not have responded quickly enough to trip the unit and Vitiate fast transfer. Grid relaying would have isolated the faulted grid from the unit, leaving the unit tied (via 4885) to the dead South bus at Ashe. This loss of load would have caused turbine speed to increase. The turbine Overspeed Protection Controller (OPC) would cause a reactor scram and a Recirculation Pump Trip (RPT) by depressurizing the OPC hydraulic header. Most likely the acceleration would be too fast to be caught by the Overspeed Protection Controller (OPC) and the turbine would trip on mechanical or electrical overspeed signals. The turbine trip would ultimately trip the unit lock out relays which, in turn, would trip the 500KV breakers and initiate fast transfer.

If the. OPC terminated the acceleration before an overspeed trip occurred, it is possible that the OPC would try to control the turbine at synchronous speed until operator action or anti-motoring initiated the turbine trip/generator trip/fast transfer sequence. (The "anti-motoring" signal is generated. by a low differential pressure across the high pressure turbine and has a 60 second time delay.)

In either case if the unit and grid would be disconnected for more than a few cycles and, when fast transfer occured, rotating loads could be re-energized when out of phase with, the Startup transformer, potentially damaging the motors or the transformer. While this presents a commercial risk,'ritical equipment would not be endangered since such equipment is normally in a standby configuration. Sufficient redundant equipment would be available to protect the health and safety of the public.

NRC Form 355A (589)

NRC FOAM 366A U.S. NUCLEAR REGULATORY COMMISSION (669) APPAOVEO OMB NO, 31500104 EXPIRES: 4/30/92 LICENSEE EV~ REPORT (LER) ATED BURDEN PER RESPONSE TO COMPLY WTH THIS AMATION COLLECTION REQUEST( 500 HRS. FORWARD MMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH IP630), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (315001041, OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, OC 20503.

FACILITY NAME ('I) DOCKET NUMBER (2) LER NUMBER LB) PAGE (3)

YEAR SEQUENTIAL II/SI REvrsloN NUMBER  %% NUMOER Washington Nuclear Plant - Unit 2 o s o o o 3 979 1 017: 0 0 0 5oFO 6 TEXT ///moro Aooco (I ror/rr/rod, Ir44 odd/o'orro/NRC Form 36643/ (IT)

Similar Events Other WNP-2 LERs related to offsite grid disturbances are:

LER 85-002 Failed Potential Transformer at a BPA Substation Caused a WNP-2 Generator Trip and Reactor Scram.

LER 85-003 Erroneous 500KV breaker open signal. from BPA substation caused by faulty microwave link.

LER 86-022 Diesel Generator start caused by momentary loss of 230KV power due to a trip at a BPA substation.

LER 90-024 Diesel Generator 82 start on grid voltage and frequency fluctuation caused by a thunderstorm.

LER 85-002 corrective actions included extending the delay time for ground relays from 0.25 to 0.5 sec. This allows BPA relaying to clear certain substation faults without unnecessarily tripping WNP-2. The relay functioned as designed in this event.,

The corrective actions for LER 85-003 do not relate to this event. The other two LERs did not require corrective action since all equipment responded as expected.

EIIS Information Text REference.

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