ML20082C608

Ro:On 831109,while Units Out of Svc for Planned Maint,Lee 6C Gas Turbine Tripped off-line,deenergizing Standby Buses & Placing Units in Degraded Mode Beyond Tech Spec Limit.Cause Undetermined.Next Rept by 831118

ML20082C608
Person / Time
Site:	Oconee
Issue date:	11/14/1983
From:	Tucker H DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8311220151
Download: ML20082C608 (3)

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Dune POWER GOMPANY P.O. box 33189 CHARLOrTE, N.C. 28242 HAL B. TUCKER TELEPHOffE vicee. ., (704)373-453:

November 14, 1983 hh[10V18 4 g.* Jg 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, and -287

Dear Mr. O'Reilly:

Please find attached a Special 5-Day Report concerning the loss of power on both standby buses with both Keowee units out of service. This report is submitted pursuant to Oconee 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,

/b / e Hal B. Tucker JCP/php i

Attachment l

cc: Document Control Desk U. S. Nuclear Regulatory Commission Washington, D. C. 20555 l

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 Regulatory Commission Washington, D. C. 20555

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8311220151 831114 nmernconi i PDR ADOCK 05000269 J S PDR ~ LLI f l

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JP0/HBT/JCP Noveb:r 14, 1983 Duke Power Company-Oconee Nuclear Station Special Report Lee Steam Station Gas Turbine Tripped Deenergizing Both Standby Buses While Both Keowee Units Were Out of Service On November 9, 1983 with Keowee Units 1 and 2 out of service for planned maintenance, Lee "6C" Gas 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 1326 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.04543e-4 months <br /> on' November 9, 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 to reduce power since an Oconee procedure concerning the operation of the 100 KV power supply had more restrictive constraints.

The 10 percent per hour shutdowns were started on Units 1 and 3. Lee "5C" Gas Turbine was placed on line t7 the system grid at 1340 hours0.0155 days <br />0.372 hours <br />0.00222 weeks <br />5.0987e-4 months <br /> and Lee "6C" Gas Turbine was restarted and reetergized the standby buses at 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on November 9, 1983. The shutdov .equirement was subsequently lifted. 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 time. When the trip occurred, an operator was dispatched to the turbine panel to note specific alarms. The five alarms 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 i but is similar to the September 29, 1983, October 26, 1983, and October 28, j 1933 incidents (reference the September 27, October 4, October 31, and November 2, 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.

j 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

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trip the-turbine. The pressure switch was checked and found to be operative.

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. t JP0/HBT/JCP Novzmhar 14, 1983 The corbustion 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.

The recorder signal was still blocked as a result of the September-29, 1983 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 deter-mined. 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

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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. Further corrective actions to prevent this recurring event are pending evaluation and implementation. It is antici-pated that additional information concerning these actions will be transmitted to you by November 18,.1983.

While both Keowee units were out-of-service and the standby buses were not energized by Lee, power was always available from 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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