ML20078P884

Ro:On 831026,w/unit Out of Svc for Maint,Lee Steam Station Gas Turbine Tripped,Deenergizing Both Standby Buses.Cause Not Determined.Redundant Buses Available

ML20078P884
Person / Time
Site:	Oconee
Issue date:	10/31/1983
From:	Tucker H DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8311090259
Download: ML20078P884 (3)

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4 DuxE POWER GOMPANY P.O. HOx 33180 CHAMLOTTE. N.O. 28242 [

HAL H. TUCK!:R V[ TELEPHOME October 31, 1983 gy.o *ara-4=>

Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30303 Re: Oconee Nuclear Station Docket Nos. 50-269, -270, -287

Dear Mr. O'Reilly:

Please find attached a Special 5-Day Report concerning the loss of power on both standby buses with Keowee Unit 1 out of service. This report is submitted pursuant to Oconce Nuclear Station Technical Specification 3.7.9 and describes an incident which is considered to be of no significance with respect to its effect on the health and safety of the public.

Very truly yours, f$.f Hal B. Tucker

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JCP/php Attachment cc: Document Control Desk U. S. Nuclear Regulatory Commission Washington, D. C. 20555 INPfJ 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 Regulatory Commission Washington, D. C. 20555

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JP0/HBT/JCP October 31, 1983 Duke Power Company Oconee Nuclear Station Special Report Lee Steam Station Gas Turbine Tripped Deenergizing Both Standby Buses While Keowee Unit 1 Was Out of Service On October 26, 1983 with Keowee Unit 1 out of service for planned maintenance and Keowee Unit 2 available (returned to service September 25, 1983) at 0355 hours0.00411 days <br />0.0986 hours <br />5.869709e-4 weeks <br />1.350775e-4 months <br />), Lee "6C" Cas Turbine was being used to energize both Oconee 4160V Standby Buses as required by Technical Specification 3.7.4. Lee "6C" tripped off line at 2205 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.390025e-4 months <br /> on October 26, 1983, thereby deenergizing both standby buses and placing the two operating Oconee units in a degraded mode beyond that allowed by Technical Specification 3.7.4.a. This incident is reportable to the Nuclear Regulatory Commission in accordance with Technical Specification 3.7.9.

A safety evaluation was performed pursuant to Technical Specification 3.7.9 and the decision was made that continued operation of the units was allowed since power from a Lee gas turbine would be regained in a short period of time. Lee "5C" Gas Turbine was placed on line to the system grid at 2218 hours0.0257 days <br />0.616 hours <br />0.00367 weeks <br />8.43949e-4 months <br /> and Lee "6C" Cas Turbine was restarted and reenergized the standby buses at 2224 hours0.0257 days <br />0.618 hours <br />0.00368 weeks <br />8.46232e-4 months <br /> on October 26, 1983. The total time the standby buses were unavailable was 19 minutes.

The exact cause of the Lee "6C" gas turbine trip cannot be determined at this cime. When the trip occurred, an operator was dispatched to the turbine panel to note specific alarms. The five alarcs noted were:

1) 4500 KVA Main Transformer Trip

2) Turbine Overspeed Trip

3) Combustion out-of-fire or Recorder off

4) Low Lube Oil Pressure

5) Loss of AC voltage Lee Steam Station does not have an event recorder so the order of the alarms could not be determined. No other alarms or protective relay targets were noted. Therefore, this incident is not similar to the September 22, 1983 trip but is similar to the September 29, 1983 incident (reference the September 27, 1983 and October 4, 1983 H. B. Tucker Special 5-Day Reports).

Since the operating unit supplies its own auxiliaries, any trip would cause a loss of AC voltage which in turn would cause the other four alarms to annunciate.

Each alarm was investigated to determine if it could have initiated the trip.

The 4500 KVA Main Transformer was checked for problems and none were noted.

The turbine overspeed trip mechanism was found to be still set, thereby eliminating the possibility of an overspeed trip. However, if the turbine pressure switch failed or malfunctioned, a turbine overspeed trip alarm would annunciate and trip the turbine. The pressure switch was checked and found to be operative.

The combustion out-of-fire and recorder off alarm is a dual alarm. If any of the twelve combustors fail to ignite the unit will trip and cause the alarm.

e JP0/HBT/JCP October 31, 1983 I'

The recorder signal was still blocked as a result of the last trip so a malfunction or loss of power could not trip the unit. The lube oil pressure to the turbine, the pump, and the supply system appeared good when checked; however, a spurious actuation of the pressure switch could have caused the alarm and trip. Since all five alarms can be explained and the order of the alarms cannot be determined, the direct cause of the trip cannot be determined.

An investigation is still underway to determine the cause and the results will be supplied in supplemental correspondence when available.

At the time of the incident, both the Lee "4C" and "5C" gas turbines were available, and the Lee "5C" was immediately placed in startup mode. Lee "5C" became ready for start prior to Lee "6C"; however, it was decided to place Lee "5C" on line to the system grid as a backup so that Lee "6C" could be placed on line to Oconee's 4160 Standby Buses.

While one Keowee unit was out-of-service and the standby buses were not energized by Lee, power was always available from Keowee Unit 2 via the underground feeder circuit required by Technical Specification 3.7.4. Also available was the normal Duke Power Company transmission system to the 230 KV switchyard via at least two 230 KV transmission lines on separate towers as required by Technical Specification 3.7.1.

During this incident both the Lee "4C" and Lee "5C" Gas Turbines were available and could have energized the Standby Buses within one hour. The probability of losing offsite power during this event is very small; therefore, the health and safety of the public were not endangered.

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