ML18010B119

LER 93-007-00:on 930523,SUT to Auxiliary Bus E Supply Breaker 121 Failed to Open Automatically Due to Misaligned Mechanism Operated Cell Switch in Breaker 122.Insp of Other 6.9 Kv Breakers performed.W/930622 Ltr

ML18010B119
Person / Time
Site:	Harris
Issue date:	06/22/1993
From:	Robinson W, Verrilli M CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
HO-930110, LER-93-007-01, LER-93-7-1, NUDOCS 9306280017
Download: ML18010B119 (18)

Text

ACCEI ERP DOCU1VIENT DIS~> BUTION SYSTEM

~D INFORMATION l REGULnWz wY DISTRIBU'l~ SYSTEM (RIDS)

I ACCESS:ON NBR:9306280017 DOC.DATE: 93/06/22 NOTARIZED: NO DOCKET FACIAL".50-400 Shearon Harris Nuclear Power Plant, Unit 1, Carolina 05000400 AUTH. NAME AUTHOR AFFILIATION VERILLI,M. Carolina Power & Light Co.

ROBINSON,W.R. Carolina Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 93-007-00:on 930523,unplanned ESF actuationoccured when "B"emergency diesel generator started on loss of power to 1B-SB safety bus.C/As:Training,procedure rev & enhancements W/930622 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), ncident Rpt, etc.

NOTES:Application for permit renewal filed.'5000400 RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-1 LA 1 1 PD2-1 PD 1 1 LE,N 1 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/DRCH/HHFB 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRIL/RPEB 1 1 NRR/DRPW/OEAB 1 1 NRR/DRSS/PRPB 2 2 ,RR SPLB 1 1 NRR/DSSA/SRXB 1 1 EQF- 02 1 '1 RES/DSIR/EIB 1 1 GN FILE Ol 1 1 EXTERNAL EG&G BRYCE i J ~ H 2 2 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHYiG.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL'RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTEI CONTACI'HE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEEDI FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32

Carolina Power 4 Ught Company AR PLANT P.O. Box 165 Cc'e" y Ceiresponaence New Hill, North Carolina 27562 Letter Number: HO-930110 U.S. Nuclear Regulatory Commission ATTN: NRC Document Control Desk Washington, DC 20555 SHEARON HARRIS NUCLEAR POWER PLANT UNIT 1 DOCKET NO. 50-400 LICENSE NO. NPF-63 LICENSEE EVENT REPORT 93-007-00 Gentlemen:

In accordance with Title 10 to the Code of Federal Regulations, the enclosed Licensee Event Report is submitted. This report fulfills the requirement for a written report within thirty (30) days of a reportable occurrence and is in accordance with the format set forth in NUREG-1022, September 1983.

Very truly yours, W. R. Robinson General Manager Harris Nuclear Plant MV: kls Enclosure cc: Mr. S. D. Ebneter (NRC - RII)

Mr. N. B. Le (NRC - PM/NRR)

Mr. J. E. Tedrow (NRC - SHNPP) i40067 MEM/LER93-007/1/Osl 9306280017 V5~000400 i

NR FORM 366 U.S. NUCLEAR REGUlATORY COMMISSION APPROVED BY OMB ND. 31600104 EXPIRES 6)31/96 (5-92)

ESTIHATED BURDEN PER RESPONSE TO COMPLY WITH LICENSEE EVENT REPORT (LER) THIS INFORMATION COLLECTIOH REQUEST: 50.0 HRS.

FORWARD COMMENTS REGARDIHG BURDEN ESTIMATE TO THE INFORMATION AHD RECORDS MANAGEMENT BRANCH (See reverse for required number of digits/characters for each block) (HHBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AHD BUDGET WASHIHGTOk DC 20503.

FAC(l)TY NAME (1) Shearon Harris Nuclear Plant-Unit gl DOCKET NUMBER (2) PAGE (3) 05000 400 1 OF 5 TITLE (4) Unplanned Engineered Safety Feature Actuation when "B" Emergency Diesel Generator started on loss of ower to the 1B-SB Safet Bus.

EVENT DATE(6) LER NUMBER 8) REPORT DATE OTHER FACILITIES INVOLVED I FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV IS I OH MONTH DAY YEAR 05000 NUMBER HUHBER FACILITY NAME DOCKET NUMBER 23 93 93 007 00 6 22 93 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT T 0 THE REOUIREMENTS OF 10 CFR 9: Check one or more) 1 MODE (9) 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73. 71(b) 20.405(a)(1)(i) 50.36(c) (1) 50.73(a)(2)(v) 73.71(c)

POWER LEVEL (10) 15 ~O 0 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii) OTHER 20.405(a)(1)(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) (Specify in Abstract below 20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) and in Text, 50.73(a)(2)(iii) 50.73(a)(2)(x) HRC Form 366A) 20.405(a)(1)(v)

LICENSEE CONTACT FOR THIS I.ER I2I TELEPHONE HUMBER (Include Area Code)

NAME Michael Verrilli (919) 362-2303 COMPI.ETE OHE I.INE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13 REPORTABLE REPORTABLE CAUSE SYSTEM COMPONENT MANUFACTURER CAUSE SYSTEM COMPONENT MANUFACTURER TO HPRDS TO NPRDS CL B455 SUPPLEMENTAL REPORT EXPECTED 14) MONTH DAY YEAR EXPECTED YES SUBMISSION (If yes, coop(ete EXPECTED SUBHISSIOH DATE). X NO DATE ((6)

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (IB)

On May 23, 1993 the Startup Transformer to Auxiliary Bus E supply breaker 121 failed to open automata. cally when the corresponding Auxiliary Transformer supply breaker 122 was closed. This resulted in both transformers feeding the same bus. After troubleshooting, recommendations were made and action taken to manually open breaker 121. Upon opening breaker 121, emergency bus B-SB supply breaker 125 opened on interlock resulting in deenergizing of the B-SB bus and automatic start and loading of the 'B'mergency Diesel Generator (EDG). Breaker 121 failed to switch automatically open due to a misaligned Mechanism Operated Cellcause (MOC) of this in breaker 122, which defeated the auto-open interlock. The event was determined to be insufficient training and procedural controls to ensure that the MOC switch was properly aligned following maintenance.

Corrective actions will include training, procedure revisions and enhancements to ensure proper MOC switch alignment in applicable breakers.

This event is being reported per 10CFR50.72(a)(2)(iv) as an unplanned actuation of an Engineered Safety Feature.

NRC FORM 366

NRC FORM 3BBA U.S. NUCLEAR REGULATORY CO APPROVED BY OMB NO. 31600104 EXP IRES 5/31/95 (5-92)

ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.

FORWARD COMMENTS REGARDIHG BURDEN ESTIMATE TO LICENSEE EVENT REPORT (LER) THE IHFORMATION AHD RECORDS MANAGEMEHT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555.0001, AHD TO THE PAPERWORK REDUCTION PROJECT (3150 0104), OFFICE OF MANAGEMENT AND BUDGET WASHINGTON DC 20503.

FACILITY NAME III DOCKET NUMBER 2 LER NUMBER IB PAGE I3 Shearon Harris Nuclear Plant YEAR SEQUENTIAL REVI SI OH Unit g1 osooo/4oo 2 OF 5 93 007 00 TEXT If more s ce is r uired use additional co ies of NRC Form 366A II)I EVENT DESCRIPTION:

On May 23, 1993 during power ascension following a one day outage, Operators were swapping auxiliary loads from the Startup Transformers (SUTs) to Unit Auxiliary Transformers (UATs) At 1555 while attempting to swap the loads on Auxiliary Bus 'E', the SUT to Bus 'E'upply breaker 121 failed to open automatically when UAT supply to Bus 'E'reaker 122 was closed. This resulted in Bus 'E'eing supplied by both transformers.

Maintenance and Technical Support personnel were contacted and research efforts to determine possible causes and appropriate corrective action were commenced. A concern was identified associated with circulating currents through both transformers due to the parallel operation, which could result in transformer failure. This concern provided a sense of urgency to take prompt action to open one of the breakers and eliminate the parallel supply line-up. Operators observed normal stable currents through both transformers as indicated on the main control board, and discussed which breaker they would open in the event of rapidly increasing transformer currents. It was concluded that the UAT supply breaker 122 would be opened if this were to occur. This was based on the assumption that the circuitry may not recognize that breaker 122 is actually closed. The control room staff's main focus of concern was the possibility of losing "B-SB".

power to Aux Bus "E", which would result in a loss of Emergency Bus Following research and troubleshooting efforts by Operations, Maintenance, and Technical Support personnel, a conclusion was reached that breaker 121 should be manually opened. This was recommended to the control room staff and at 1732 breaker 121 was locally opened. Emergency Bus "B-SB" supply breaker 125 immediately tripped open on interlock, deenergizing the bus and resulting in an automatic start and loading of the B-SB Emergency Diesel Generator.

Upon subsequent inspection of breaker 122, Maintenance personnel discovered that the Mechanism Operated Cell (MOC) switch was in the "Breaker OPEN" position. This MOC switch is physically located on the inside wall of the breaker cabinet and during the breaker rack-in process engages with an attachment on the left outside corner of the breaker called an actuating angle. When properly aligned and engaged this switch rotates electrical contacts when the breaker is opened or closed. The MOC switch was in the "Breaker OPEN" position due to these components being misaligned as a result of the last rack-out / rack-in evolution. Therefore, when breaker 121 was locally opened, with the MOC switch in breaker 122 not properly engaged, both breakers erroneously appeared open to the interlock logic and breaker 125 tripped open automatically.

NRC FORM 366A 5-92

NR 'FORH 366A APPROVED BY OHB NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPOHSE TO C(NPLY IIITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.

FORNARD COMMENTS REGARDIHG BURDEN ESTIMATE TO LICENSEE EVENT REPORT (LER) THE IHFORMATIOH AHD RECORDS MANAGEMENT BRANCH (MHBB 7714 ) g U S ~ NUCLEAR REGULATORY COMMI SS I ON g MASHIHGTON, DC 20555-0001 AND TO THE PAPERMORK REDUCTION PROJECT (3140.0104), OFFICE OF MANAGEMENT AHD BUDGET IIASHINGTON DC 20503.

FACILITY NAHE (1) DOCKET NUHBER (2) LER NUHBER (6 PAGE (3)

Shearon Harris Nuclear Plant YEAR SEQUENTIAL REVISION Unit gl 05000/400 3 OF 5 93 007 00 TEXT (lf more space is required, use additional copies of NRC Form 36Q) (17)

EVENT DESCRIPTION: (Cont.)

Although misalignment was evident, the MOC switch had to be engaged with the breaker, at least up until auxiliary loads were swapped from the UATs to SUTs on May 21, 1993; otherwise, breaker 125 would have received a trip signal earlier. Based on this, the MOC switch most likely slipped off the MOC actuating angle either during the previous auxiliary load swap evolution or two days later during this event when breaker 122 was closed.

A scar on the damaged MOC actuating angle indicates that the switch most likely slipped off the angle when breaker 122 was closed on May 23, 1993.

CAUSE:

The cause of this event was the improper alignment of the MOC switch during the rack-in of breaker 122 that occurred on November 20, 1992 and subsequent contact "slip-off" on May 23, 1993. This condition created a false "breaker open" signal and resulted in the automatic trip of breaker 125 on interlock. The following factors contributed to the improper switch alignment; lack of knowledge on the part of operators regarding the proper method for checking MOC alignment during breaker rack-in and inadequate maintenance procedures resulting in improper installation and position verification of the MOC switch and actuating angle ~

SAPETY SIGNIPICANCE:

There were no safety consequences as a result of this event. The "B" Emergency Diesel Generator started automatically upon the loss of power to the "B" Safety bus and was available for emergency loads. The "B" Essential Services Chilled Water Circulating Pump (P-4) did not automatically start as designed, but did start upon a manual start signal.

This event is being reported per 10CFR50.72(a)(2)(iv) as an unplanned actuation of an Engineered Safety Feature (ESF). Although similar misalignment problems with 6.9 KV breakers have occurred in the past, none have resulted in a reportable condition. Operator training was conducted following an event that occurred in 1988, but was not incorporated into the initial or continuing training programs to ensure a knowledge of this condition was maintained.

CORRECTIVE ACTIONS:

1. An inspection of other 6.9 KV breakers was performed to ensure proper MOC switch alignment. No other discrepancies were identified.

2. The problem with the Essential Services Chilled Water Circulating Pump (P-4) was corrected by Work Request and Authorization (WR&A)

N93-AFKP1, which replaced the supply breaker's closing coil.

3. Training is being provided to operations personnel on proper rack-in methods to verify MOC switch alignment during 6.9 KV breaker evolutions.

NRC FORM 366A (5-92)

NRC FORH 366A U.S. NUCLEAR REGULATORY CONNISSION APPROVEO BY OHB HO. 3150.0104 EXP I RES 5/31/95 (5-92)

ESTINATED BURDEN PER RESPOHSE TO COHPLY MITH THIS INFORHATION COLLECTION REQUEST: 50.0 HRS.

FORMARD COHHEHTS REGARDIHG BURDEN ESTIHATE TO LICENSEE EVENT REPORT (LER) THE IHFORHATION AND RECORDS HANAGEHENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY COHHISSIOH, MASHIHGTON, DC 20555-0001~ AND TO THE PAPERMORK REDUCTION PROJECT (3140 0104), OFFICE OF HAHAGEHENT AND BUDGET MASHIHGTON DC 20503 HANE (1) DXKET HUHBER (2) LER HUNBER (6) PAGE (3)

'ACILITY Shearon Harris Nuclear Plant YEAR SEQUENTIAL REVISION Unit N1 05000/400 4 OF 5 93 007 00 CORRECTIVE ACTIONS: (CONT.)

4. Initial and Continuing Training programs will be changed to incorporate the training required by corrective action 42.

5. Maintenance procedures will be developed and revised as necessary to include inspection of MOC switch and actuating angle condition and a'gnment .

6. A placard will be installed inside 6.9 KV breakers to indicate the location for conducting MOC alignment verification.

EIIS INFORMATION:

ESCW P-4 Pump - KM NRC FORH 366A (5-92)

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D DOCUINENT DIS > 8UTION SYSTEM REGU Y INFORMATION DISTRIBU h YSTEM (RIDS)

ACCESS:ON NBR:9306280017 DOC.DATE: 93/06/22 NOTARIZED: NO DOCKET ¹ FACIE:50-400 Shearon Harris Nuclear Power Plant, Unit 1, Carolina 05000400 AUTH. NAME AUTHOR AFFILIATION VERILLI,M. Carolina Power & Light Co.

=

ROBINSON,W.R. Carolina Power 6 Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 93-007-00:on 930523,unplanned ESF actuationoccured when "B"emergency diesel generator started on 1'oss of power to D 1B-SB safety bus.C/As:Training,procedure rev a enhancements W/930622 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), ncident Rpt, etc.

NOTES:Application for permit renewal filed. 05000400 A RECIPIENT D RECIPIENT COPIES COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-1 LA 1 1 PD2-1 PD 1 1 D LE,N 1 1-INTERNAL: ACNW AEOD/DOA 2:21 1

ACRS AEOD/DSP/TPAB 2

1 2

1 AEOD/ROAB/DSP 2 2 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/DRCH/HHFB 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRIL/RPEB 1 1 NRR/DRPW/OEAB 1 1 NRR/DRSS/PRPB 2 2 NRR DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1 EG - E 02 1 1 RES/DSIR/EIB 1 1 RGN2 FILE 01 1 1 EXTERNAL: EGGG BRYCEiJ.H 2 2 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 D

A D

D NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTBI CONTACI'HE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISIRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEEDl FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 32 ENCL 32

I ~

~'

ForrYl 24w Carolina Power & Light Company AR PLANT P.O. Box 165 Company Correspondence New Hill, North Carolina 27562 "U~ 2 2 ~o.y Letter Number: HO-930110 U.S. Nuclear Regulatory Commission

=ATTN: NRC Document Control Desk Washington, DC 20555 SHEARON HARRIS NUCLEAR POWER PLANT UNIT 1 DOCKET NO. 50-400 LICENSE NO. NPF-.63 LICENSEE EVENT REPORT 93-007-00 Gentlemen:

In accordance with Title 10 to the Code of Federal Regulations, the enclosed Licensee Event Report is submitted. This report fulfills the requirement for a written report within thirty (30) days of a reportable occurrence and is in accordance with the format set forth in NUREG-1022, September 1983.

Very truly yours, 9~4 W. R. Robinson General Manager Harris Nuclear Plant MV:kls Enclosure I

cc: Mr. S. D. Ebneter (NRC - RII)

Mr. N. B. Le (NRC - PM/NRR)

Mr. J. E. Tedrow (NRC - SHNPP) z4006

('EM/LER93-007/1/OS1 gyp g28pp 1 7 9 o622 PDR ADOCK P

NRC FORM 365 U.S. NUCLEAR REGULATORY COMMISSION OMB NO. 3160 0104 EXPIRES 6]31/85 (5-92)

ESTIMATED BURDEN PER RESPONSE TO COHPLY WITH LICENSEE EVENT REPORT (LER) THIS INFORMATION COLLECTION REQUEST: 50.0 HRS ~

FORWARD COHHENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AHD RECORDS MANAGEMENT BRANCH (See reverse for required number of digits/characters for each block) (MHBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AHD TO THE PAPERWORK REDUCTION PROJECT (3150.0104), OFFICE OF HAHAGEMEHT AND BUDGET WASHINGTON DC 20503.

FACILITYNAMEII) Shearon Harris Nuclear Plant-Unit g1 DOCKET NUMBER I2) PAGE I3) 05000 400 1OFS TITLE(4I Unplanned Engineered Safety Feature Actuation when "B" Emergency Diesel Generator started on loss of ower to the 1B-SB Safet Bus.

EVEHT DATE (5 LER NUMBER 5 REPORT DATE OTHER FACILITIES INVOLVED REVIS!ON FACILITY NAME DOCKET NUMBER SEQUENTIAL MONTH DAY YEAR YEAR HUHBER NUMBER MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 23 93 93 007 00 22 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REDUIREMENTS OF 10 CFR 5: Check one or more) 111 MODE <9) 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b) 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

POWER LEVEL IIO) 15~0 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vII) OTHER 20.405(a)(1)(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) (S p ecif y>n Abstract below 20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) and in Text, 50.73(a)(2)(iii) 50.73(a)(2)(x) NRC Form 366A) 20.405(a)(1)(v)

I.ICENSEE CONTACT FOR THIS I.ER 12 TELEPHONE NUMBER (Include Area Code)

NAHE Michael Verrilli (919) 362-2303 COMPLETE ONE LINE FOR EACH COMPONENT FAII.URE DESCRIBED IN THIS REPORT 13 REPORTABLE REPORTABLE CAUSE SYSTEH COMPONENT MANUFACTURER CAUSE SYSTEH COHPONEHT MANUFACTURER TO HPRDS TO NPRDS B KM CL B455 Y SUPPLEMENTAL REPORT EXPECTED 14 MONTH OAY YEAR EXPECTED YES SUBMISSION (If yes, complete EXPECTED SUBMISSIOH DATE).

X NO DATE IIEI ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (IB)

On May 23, 1993 the Startup Transformer to Auxiliary Bus E supply breaker 121 failed to open automat3.cally when the corresponding Auxiliary Transformer supply breaker 122 was closed. This resulted in both transformers feeding the same bus. After troubleshooting, recommendations were made and action taken to manually open breaker 121. Upon, opening breaker 121, emergency bus B-SB supply breaker 125 opened on interlock resulting in deenergizing of the B-SB bus and automatic start and loading of the 'B'mergency Diesel Generator (EDG). Breaker 121 failed to Cell (MOC) switch automatically open due to a misaligned Mechanism Operated The cause of this in breaker 122, which defeated the auto-open interlock.

event was determined to be insufficient training and procedural controls to ensure that the MOC switch was properly aligned following maintenance.

Corrective actions will include training, procedure revisions and breakers..

enhancements to ensure proper MOC switch alignment in applicable This event is being reported per 10CFR50.72(a)(2)(iv) as an unplanned actuation of an Engineered Safety Feature.

NRC FORM 366

U.S. NUCI.EAR REGUULTORY COMMISSION MB NO. 31600'I04 (5.92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.

FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO LICENSEE EVENT REPORT (LER) THE INFORMATION AND RECORDS MAHAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHIHGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET WASHINGTON DC 20503.

FACILITY NAME II DOCKET NUMBER I2I LER NUMBER IB PAGE I3 Shearon Harris Nuclear Plant YEAR'3 SEQUENTIAL REVISION Unit gl 05000/400 2 OF 5 007 00 TEXT If more s ace is r vired vse additional co ies of NRC Form 366A IITI EVENT DESCRIPTION:

On May 23, 1993 during power ascension following a-one day outage, Operators were swapping auxiliary loads from the Startup Transformers (SUTs) to Unit Auxiliary Transformers (UATs). At 1555 while attempting tO swap the loads on Auxiliary Bus 'E', the SUT to Bus 'E'upply breaker 121 failed to open automatically when UAT supply to Bus 'E'reaker 122 was closed. This resulted in Bus 'E'eing supplied by both transformers.

Maintenance and Technical Support personnel were contacted and research efforts to determine possible causes and appropriate corrective action were commenced. A concern was identified associated with circulating currents through both transformers due to the parallel operation, which could result in transformer failure. This concern provided a sense of urgency to take prompt action to open one of the breakers and eliminate the parallel supply line-up. Operators observed normal stable currents through both transformers as indicated on the main control board, and discussed which breaker they would open in the event of rapidly increasing transformer currents. It was concluded that the UAT supply breaker 122 would be opened if this were to occur. This was based on the assumption that the circuitry may not recognize that breaker 122 is actually closed. The control room staff's main-focus of concern was the possibility of losing power to Aux Bus "E", which would result in a loss of Emergency Bus "B-SB".

Following research and troubleshooting efforts by Operations, Maintenance, and Technical Support personnel, a conclusion was reached that breaker 121 should be manually opened. This was recommended to the control room staff and at 1732 breaker 121 was locally opened. Emergency Bus "B-SB" supply breaker 125 immediately tripped open on interlock, deenergizing the bus in an automatic start and loading of the B-SB Emergency Diesel and'esulting Generator.

Upon subsequent inspection of breaker 122, Maintenance personnel di'scovered that the Mechanism Operated Cell (MOC) switch was in the "Breaker OPEN" position. This MOC switch is physically located on the inside wall of the breaker cabinet and during the breaker rack-in process engages with an attachment on the left outside corner of the breaker called an actuating angle. When properly aligned and engaged this switch rotates electrical contacts when the breaker is opened or closed. The MOC switch was in the "Breaker OPEN" position due to these components being misaligned as a result of the last rack-out / rack-in evolution. Therefore, when breaker 121 was locally opened, with the MOC switch in breaker 122 not properly engaged, both breakers erroneously appeared open to the interlock logic and breaker 125 tripped open automatically.

NRC FORM 366A 5-92

NRC FORH 366A U.S. NUCLEAR REGU PROVE D BY OHB NO. 3150 ~ 0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY lIITH THIS INFORMATION COLLECTION REQUEST: 50 0 HRS.

FORIIARD COMMENTS REGARDING BURDEN ESTIMATE TO LICENSEE EVENT REPORT (LER) THE INFORMATION AND RECORDS MANAGEHEHT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, MASHINGTON, DC 20555-0001 AND TO THE PAPERNORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET llASHINGTON DC 20503.

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

Shearon Harris Nuclear Plant YEAR SEQUENTIAL REVISION Unit g1 05000/400 3 OF 5 93 007 00 TEXT (If more space is required. use additional copies of NRC Form 366A) (17)

EVENT DESCRIPTION: (Cont.)

Although misalignment was evident, the MOC switch had to be engaged with the breaker, at least up until auxiliary loads were swapped from the UATs to SUTs on May 21, 1993; otherwise, breaker 125 would have received a trip signal earlier. Based on this, the MOC switch most likely slipped off the MOC actuating angle either during the previous auxiliary load swap evolution or two days later during this event when breaker 122 was closed.

A scar on the damaged MOC actuating angle indicates that the switch most likely slipped of f the angle when breaker 122 was closed on May 23, 1993.

CAUSE:

The cause of this event was the improper alignment of the MOC switch during the rack-in of breaker 122 that occurred on November 20, 1992 and subsequent contact "slip-off" on May 23, 1993. This condition created a false "breaker open" signal and resulted in the automatic trip of breaker 125 on interlock. The following factors contributed to the improper switch alignment; lack of knowledge on the part of operators regarding the proper method for checking MOC alignment during breaker rack-in and inadequate maintenance procedures resulting in improper installation and 'position verification of the MOC switch and actuating angle.

SAFETY SIGNIFICANCE!

There were no safety consequences as a result of this event. The "B" Emergency Diesel Generator started automatically upon the loss of power to the "B" Safety bus and was available for emergency loads. The "B" Essential -Services, Chilled Water Circulating Pump (P-4) did not automati.cally start as designed, but did start upon a manual start signal.

This event is being reported per 10CFR50.72(a)(2)(iv) as an unplanned actuation of an Engineered Safety Feature (ESF). Although similar misalignment problems with 6.9 KV breakers have occurred in the past, none have resulted in a reportable condition. Operator training was conducted following an event that occurred in 1988, but was not incorporated into the initial orwas continuing training programs to ensure a knowledge of this maintained.

condition CORRECTIVE ACTIONS:

1. An inspection of other 6.9 KV breakers was performed to ensure proper MOC switch alignment. No other discrepancies were identified.

2. The problem with the Essential Services Chilled Water Circulating Pump (P-4) was corrected by Work Request and Authorization (WR6A) 593-AFKP1, which replaced the supply breaker's closing coil.

3. Training is being provided to operations personnel on proper methods to verify MOC switch alignment during 6.9 KV breaker rack-in evolutions.

NRC FORM 366A (5-92)

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NRC FORH 366A U.S. NUCLEAR REGULATORY COHHISS ION APPROVED BY OHB NO. 3150-0104

~ ' (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COHPLY 'WITH THIS INFORHATION COLLECTION REQUEST: 50.0 HRS.

FORWARD COHMEHTS REGARDING BURDEN ESTIMATE TO LICENSEE'VENT REPORT (LER) THE INFORMATION AHD RECORDS HANAGEHENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COHHISSION, WASHINGTON, DC 20555-000'I AHD TO THE PAPERWORK REDUCTION PROJECT (3140.0'l04), OFFICE OF MANAGEHENT AND BUDGET WASHINGTON DC 20503.

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

Shearon Harris Nuclear Plant YEAR SEQUENTIAL REVISION Unit g1 05000/400 4 OF 5 93 007 00 CORRECTIVE ACTIONS: (CONT.)

Initial and Continuing Training programs will be changed to incorporate the training required by corrective action g2.

5. Maintenance procedures will be developed and revised as necessary to include inspection of MOC switch and actuating angle condition and alignment .

6. A placard will be installed inside 6.9 KV breakers to indicate the location for conducting MOC alignment verification.

EIIS INFORMATION:

ESCW P-4 Pump - KM HRC FORH 366A (5-92)

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