ML20024C423

LER 83-011/03L-0:on 830525,lockout Indication Received for Startup Transformer CT3.Cause unknown.CT3 Energized. W/830624 Ltr

ML20024C423
Person / Time
Site:	Oconee
Issue date:	06/24/1983
From:	Petty J, Tucker H DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
LER-83-011-03L-01, LER-83-11-3L-1, NUDOCS 8307120613
Download: ML20024C423 (3)

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EVENT DESCRIPTION ANo PROBABLE CONSEQUENCES O10 l o l2 l l 0n May 25,1983 at 1542, a lockout Yndication was received for scart-up trans- l l o j a l l former CT3. This made the overhead emergency power path from Keowee inoperable.l The alternate power path was immediately verified. Power was available at all  ;

, g l o l s l l times. It was determined that this would cause no damage or excessive pressure; .

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h l1loll The cause of this occurrence is unknown. Testing of this system's components l

,;,;l revealed no failures or problems. There was speculation of a possible moisturg buildup or of a cracked insulator. Further testing will be done during the next extended Unit 3 shutdown. CT 4 was verified, and CTS was used also as y,,,,g standby. At 2240 CT3 was energized and power was restored.  ;

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Duke Power Company Oconee Nuclear Station Report Number: R0-269/83-11 Report Date: June 24, 1983 Occurrence Date: May 25, 1983 Facility: Oconee Nuclear Station Units 1, 2, and 3, Seneca, South Carolina Identification of Occurrence: Lockout of start-up transformer CT3 caused the overbead emergency power path from Keowee to be inoperable.

Conditions Prior to Occurrence: Oconee 1 100%

Oconee 2 Cold shutdown Oconee 3 92%

Description of Occurrence: On May 25, 1983 at 1542, a fault was indicated in the fait 3 start-up bus between the start-up transformer CT3 and the feeder breakers 3TA and 3TB. This caused the lockout of the start-up transformer CT3.

This lockout cleared and de-energized CT3, its 230 kilovolt power circuit breakers (PCB), its 6900 and 4160 volt switchgear breakers, and all associated bus work. This made the overhead emergency power path from Keowee inoperable, and constituted s degraded mode per Technical Specification 3.7.2(a).

Apparent Cause of Occurrence: The cause of this occurrence is unknown. All tests performed showed no prob 1 cms and did not reveal the cause of the fault which caused the lockout. It was suggested that there may have been a possibility of a moisture buildup that cleared itself with an electrical flash. Also suggested was the possibility of a cracked insulator. Further shutdown testing will follow.

Analysis of Occurrence: Technical Specification 3.7.2(a) permits the operation of a unit for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> upon the loss of one independent on-site emergency power path, provided the alternate power path is verified operable within one hour of the loss and every eight hours thereafter. This was done. Both power sources were operable within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> of CT3's lockout. During this period of time, the 4.16 KV auxiliary system was op6rable. Therefore, power was available to the equipment required to bring the reactor to a hot shutdown. The Oconee Final Safety Analysis Report 15.8 reviewed the loss of power accidents and determined that it would not result in any fuel damage or excessive pressures on the Reactor Coolant System. Therefore, the health and safety of the public were not affected by this incident.

Corrective Acti_on: The immediate corrective action was to energize the standby bus through the standby transformer CT4, which verified the alternate path as required per Technical Specification 3.7.2(a). Standby power was transferred from CT4 to standby transformer CT5, which is supplied by combustion turbines located at the Lee Steam Station, as an extra precautionary measure. Testing was done to try to determine the cause of the lockout. A bus high potential test, a bus doble test, a relay test, and circuit breaker tests, were performed.

No problems were noted. At 2240, CT3 was energized and power was restored to the start-up bus. Further testing to determine if there still is a problem will be performed during the next extended Unit 3 shutdown.

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L 2' o DUKE POWER Go>mtNY P.O. nox 33180 CIIARLOTTE N,C. 28242e IIAL D. TUCKER 'd C P ~ ', I ~f r'. -

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(yo4) ay3 43:n June 24, 1983 4 /

Mr. James P. O'Reilly, Regional Administrator

• b U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30303 Re: Oconee Nuclear Station Docket No. 50-269

Dear Mr. O'Reilly:

Please find attached Reportable Occurrence Report R0-269/83-11. This report is submitted pursuant to Oconee Nuclear Station Technical Specification 6.6.2.1.b(2) which concerns operation in a degraded mode permitted by a ,

limiting condition for operation :.nd describes an incident which is considered to be of no significance with respect to its effect on the bealth and safety of the public.

Very truly yours, f8.

Hal B. Tucker lQ JCP/php Attachment cc: Document Control Desk U. S. Nuclear Regulatory Commission Washington, D. C. 20555 INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 Mr. J. C. Bryant NRC Resident Inspector Oconee Nuclear Station Mr. John F. Suermann Office of Nuclear Reactor Regulation U. S. Nuclear Reguletory Commission Washington, D. C. 20555

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