ML17326A201

LER 99-004-00:on 990724,reactor Tripped Due to Main Transformer Bushing Flashover.Plant Was Brought to SS & Components Were Tested & Performed Satisfactorily.With 990823 Ltr

ML17326A201
Person / Time
Site:	Calvert Cliffs
Issue date:	08/23/1999
From:	Katz P, Kirkwood J BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-99-004, NUDOCS 9908260087
Download: ML17326A201 (8)

Text

CA.'J:EMORY

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REGULATORY INPORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSXON NBR:9908260087 DOC.DATE: 99/08/23 NOTARIZED: NO DOCKET N FACIL:50-317 .Calvert Cliffs Nuclear Power Plant, Unit 1, Baltimore 05000317 AUTH.NME ., AUTHOR AFFILIATION KIRKWOOD,J.K. Baltimore Gas & Electric Co.

KATZ,P.E. Baltimore Gas & Electric Co.

RECIP.NAME RECXPIENT AFFILIATION

SUBJECT:

LER 99-004-00:on 990724,reactor tripped due to main transformer bushing flashover.Plant was brought to SS &,

components were tested & performed satisfactorily. With 990823 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

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

NOTES:

RECIPIENT COPIES RECIPIENT COPIES XD CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL LPD1-1 PD 1 1 DROMERICK,A. 1 1 INTERNAL: ACRS 1 1 FILE CENTER 1 1 NRR/DIPM/IOLB 1 1 XB 1 1 NRR/DSSA/SPLB 1 1 RES/DET/ERAB 1 . 1 RES/DRAA/OERAB 1 1 RGN1 PILE 01 1 1 EXTERNAL: L ST LOBBY WARD 1 1 LMITCO MARSHALL 1 1 NOAC POORE,W. 1 1 NOAC QUEENER, DS 1 1 NRC PDR 1 1 NUDOCS PULL TXT 1 1 NOTE TO ALL "RZDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE. TO HAVE YOUR NAME OR ORGANIZATION REMOVED FROM DISTRIBUTION LIS'I OR REDUCE THE NUMBER OF COPIES RECEIVED BY YOU OR YOUR ORGANIZATION, CONTACT THE DOCUMENT CONTRC DESK (DCD) ON EXTENSION 415-2083 FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR, 16 ENCL 16

PETER E. KATZ Baltimore Gas and Electric Company Plant General Manager Calvert Cliffs Nuclear Power Plant Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 410 4954101 A hfember of'the Constellation Energy Group August 23, 1999 U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTIO¹ Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit No. 1; Docket No. 50-317; License No. DPR 53 Licensee Event Report 99-004 Reactor Tri Due to Main Transformer Bushin Flashover The attached report is being sent to you as required under 10 CFR 50.73 guidelines. Should you have questions regarding this report, we will be pleased to discuss them with you.

Very truly yours, for Peter E. Katz Plant General Manager PEK/JKK/bjd Attachment CC: R. S. Fleishman, Esquire H. J. Miller, NRC J. E. Silberg, Esquire A. W. Dromerick, NRC S. S. Bajwa, NRC Resident Inspector, NRC R. I. McLean, DNR J. H. Walter, PSC

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9908260087 990823 PDR ADOCK 050003177 PDR S

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 06/30/2001 (6 tcSrs) Estimated burden per response to comply with this mandatory information collection request: SO hrs. Reponed lessons learned arc incorporated into thc LICENSEE EVENT REPORT (LER) licensing process and fed back to indusuy. Forward comments regarding burden estimate to the Records hlanagemcnt Branch (T4 F33, U.S. Nuclear Regulatory (Scc rcversc for required number of Commission, Washington, DC 20SSS4001, and to thc Paperwork Reduction digits/characters for each block) Project (3IS04104), Office of Management and Budget, Washington, DC 20503. If an information collection docs not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITYNAhlE (I) DOCKET NUMBER (2) PAGE (3)

Calvert Cliffs Nuclear Power Plant, Unit 1 050000 317 I OF 04 TITLE (4)

Reactor Trip Due to Main Transformer Bushing Flashover EVENTDATE 5 LER NUMBER 6 REPORT DATE 7 OTIIER FACILITIES INVOLVED 8 TACrllTY NAME DOCKET hVMBER MONnt DAY SEQUENllAE REVtslON NUMBER hUMBER MONnt DAY 050000 rACLtrYNAME DOCKET hVMBER 07 24 1999 1999 - 004 - 00 08 23, 1999-050000 OPERATING THIS REPORT IS SUBMITTED PURSUANT 0 THE REQ UIREMENTS OF 10 CFR: Check one or morc II MODE (9) 20.2201(b) 20.2203(a)(2)(v) 50.73(a)(2)(i) 50.73(a)(2)(viii)

POPOVER 20.2203 a I 20.2203 a 3 i 50.73 a 2 ii 50.73 a 2 ix LEVEL 10 100 20.2203 a 2 i 20.2203 a 3 ii 50.73 a 2 iii 73.71 20.2203 a 2 ii 20.2203 a 4 X 50.73 a 2 iv OTHER 20.2203(a 2 (iii 50.36 c (I) 50.73 a 2 (v Specify in Abstract below 20.2203(a)(2)(iv) 50.36(c)(2) 50.73(a)(2)(vii) or in NRC Form 366A LICENSEE CONTACT FOR THIS LER 12 NAME TELEPHONE NUMBER (include Area Code)

J. K. Kirkwood 410-495-2013 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED INTHIS REPORT 13 CAUSE SYSTEM CAUSE E120 SUPPLEMENTAL REPORT EXPECTED 14 EXPECTED MONnt DAY YES SUBMISSION (Ifycs, complete EXPECTED SUBMISSION DATE). X NO DATE (16)

ABSTRACT (Limitto 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)

At 1438 on July 24, 1999, Unit 1 tripped from 100 percent power due to electrical arcing (flashover) across the No. 12 Main Transformer (U-25000-12) A-phase 500 kV bushing. The main generator output breaker opened, and the Unit 1 Reactor tripped on loss of turbine load.

A thunderstorm was in progress at the time of the Unit trip with high winds and heavy rain. Witnesses observed a lightning strike near, the affected transformer.

Lightning apparently struck the A-phase 500 kV transmission line near the transformer, increasing the electrical potential beyond the insulating capabilities of the bushing, creating an electrical arc around the bushing. The arcing across the A-phase bushing affected the A-phase current flow. Protective relays sensed the abnormal condition, and opened two Switchyard Breakers (552-22 and 552-23), the Generator Field Breaker, and the Exciter breaker.

Operators responded appropriately and plant systems functioned as designed. The plant was brought to a safe shutdown condition.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME 1 DOCKET LER NUMBER I6 PAGE 6 YEAR SEQUENTIAL REVISION NUMBER NUMBER Calvert Cliffs Nuclear Power Plant, Unit 1 05000 '317 99 004 - 00 02 OF 04 TExT IMmore spece is reocnred, use eorssonel copes oi NRc Form 366'177 I. DESCRIPTION OF EVENT I

During a thunderstorm on July 24, 1999, at 1438, Unit 1 tripped from 100 percent power due to flashover across the No. 12 Hain Transformer A-phase, 500 kV (U-25000-12) bushing. The A-phase bushing (H-l, A-phase, Westinghouse Type-0 Condenser bushing) apparently flashed-over due to weather-related effects. A security guard saw lightning strike near the main transformer immediately before seeing the A-phase bushing flashover. Another security guard with a different view also reported a lightning strike in the vicinity of the main transformex'.

The transformer is a link between the turbine generator (EIIS HA-TG) and the 500 kV transmission lines leaving the plant. The turbine generator tripped on transformer high-side leads differential (indicating that there was an imbalance between phases). The reactor tripped on loss of turbine load on all four channels of the Reactor Protective System. All eight reactor trip breakers actuated, and the reactor was brought to a safe shutdown condition.

No engineered safety feature systems were actuated during this event.

II. CAUSE OF EVENT The Unit 1 Reactor trip was caused by the flashover of the U-25000-12, A-phase 500 kV bushing. The bushing apparently flashed over due to the A-phase voltage increasing beyond the insulating capabilities of the bushing caused by lightning striking the A-phase conductor.

A thunderstorm was in progress at the time of the reactor trip. High winds, heavy rain, and frequent lightning accompanied the storm. Two security guards witnessed a lightning strike in the vicinity of the affected transformer. One security guard witnessed arcing across the A-phase 500 kV bushing immediately after the lightning strike.

The arc across the bushing created an imbalance in the A-phase transformer output. The "High Side Leads Differential Current" and the "Main Generator Differential/Ground" protective relay circuits opened switchyard bxeakers 552-22 and 552-23 which isolated both Unit 1 main transformers from the switchyard, and opened the main generator field breaker and exciter breaker, causing a loss of load turbine trip and Reactor Protective System trip.

Post-event inspections of the affected transformer found a black scorch mark and holes at the top of the A-phase bushing, and a black scorch mark at the base of the bushing. There were also scorch marks on some of the transformer deluge system heat sensors and spray nozzles located near the A-phase bushing:

There was no evidence of a "direct-hit" lightning strike in the area of the A-phase bushing.

Post-event testing of the A-phase bushing indicated no internal damage to the bushing, eliminating bushing failure as a cause of the event..

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITYNAME 1 DOCKET LERNUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER NUMBER Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 99 - 004 - 00 03 OF 04 TExT (IImote space ts retfui red, use atfchuonal coptes of NRc Form 366A) (17)

III. ANALYSIS OF EVENT.

There was no undue risk to the health and safety of any member of the general public, or risk of exposure to ionizing radiation to any individual from this event. Protective relays and circuit breakers operated as designed, and the unit was brought to a safe shutdown condition without further incident.

Operators responded appropriately, and plant systems functioned as designed to stabilize the plant.

Plant Design Engineers concluded that the Lightning Protection system functioned as designed. This conclusion is based on recorded voltage and current waveform traces of the 500 kV system, and the lack of any major physical damage to the electrical hardware, structures, and ground in the vicinity of the transformer U-25000-12.

The lightning created a voltage potential surge on the A-phase. The increased potential resulted in an electrical arc from the high potential at the top of the A-phase bushing to the base of the bushing and other nearby metal components at ground potential. Evidence shows that the Lightning Protection functioned to prevent severe physical damage from the lightning. The A-phase 500 kV bushing of the No. 11 Main Transformer was not damaged. A-phase 500 kV transmission insulators were also undamaged.

This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv), Any event or condition that resulted in a manual or automatic actuation of any engineered safety feature including the Reactor Protective System.

IV. CORRECTIVE ACTIONS Immediate A. The Number 11 and 12 Main Transformers, the main generator, protective relays, and lightning protection were tested for satisfactory performance. All components performed satisfactorily.

B. The damaged A-phase secondary bushing was replaced.

C. Unit 1 was restarted on Monday, August 2, 1999.

Long-Term D. The lightning protection system will be evaluated for adequacy and acceptability.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACIUTYkAME 1 DOCKET LERNUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER NUMBER Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 99 004 - 00 04 OF 04 TEXT (I!more space is reqorred, use errrarronel copies or NRC Form 366A) (I 7)

V. ADDITIONAL INFORMATION A. Component Identification Component IEEE 803 IEEE 805 EIIS Function System ID A-phase bushing INS EL B. Previous Similar Events In 1987, an event similar to this event occurred involving flashover of the "C"-phase bushing of the same transformer (U-25000-12) during a snowstorm.

Details of the event are recorded in Licensee Event Report Number 317/87-015.