ML20080P327

Ro:On 830922,w/both Keowee Hydro Units Out of Svc for Planned Maint,Lee 6C Gas Turbine,Being Used to Energize Buses,Tripped Off Line.Both Standby Buses Deenergized & Units 1 & 3 Placed in Degraded Mode

ML20080P327
Person / Time
Site:	Oconee
Issue date:	09/27/1983
From:	Tucker H DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8310060426
Download: ML20080P327 (3)

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DUKE POWER GoneAxy

, P.O. Box 33180

, , CHAMLOTTE, N.C. 2824C II AL 11. TUCKER Teter, sone n

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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 No. 50-269, -270, and -287

Dear Mr.:

O'Reilly:

Please find' attached a Special 5-D'ay 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, Jk/8 7ksker '

Hal B. Tucker [

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

INPO Records Center Suite 1500 1 1100 circle 75 Parkway l s ' Atlanta, Georgia 30339 i

Mr. J. C. Bryant

'NRC Resident Inspector Oconee Nuclear Station Mr. John F. Suermann Office of Nuclear Reactor Regulation U. Si Nuclear Regulatory Commission Washington, D. C. 20555 '

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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 September 20, 1983, both Keowee Hydro units were taken out of service for planned maintenance. As required by Technical Specification 3.7.6, both 4160 volt standby buses were first energized by a Lee gas turbine through the 100KV transmission circuit and separated from the system grid and offsite non-safety related loads. Lee "6C" was being used to energize the buses. When it tripped off line at 1031 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.922955e-4 months <br /> on September 22, 1983, both standby buses became deenergized, and the two operating Oconee units were placed in a degraded mode beyond that allowed by Technical Specification 3.7.6. This report is submitted pursuant to Technical Specification 3.7.9, which requires a written report to be submitted within five days of this occurrence.

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. However, an Oconee procedure concerning the operation of the 100 KV power supply had more restrictive constraints and 10 percent per hour shutdowns were started on Units 1 and 3. This shutdown requirement was lifted at 1057 when power to the standby buses was restored. The total time that they were unavailable was 26 minutes.

The apparent cause of the Lee "6C" gas turbine trip was the component malfunction of the 04X relay (blocking relay) which did not block a trip signal from the 67 relay (generator reverse power relay). Personnel investigating the trip of the Lee "6C" gas turbine found the 86 GA relay (Generator Lockout) tripped. Several relays can cause the 86 GA to trip, but only the 67 relay was found to be tripped.

When supplying power to the Oconee units the 67 relay and ten other relay signals are blocked by the 04X relay to prevent non-essential relay trips from affecting the Lee gas turbines. The 04X relay was checked and found energized and should have prevented this incident. The 04X relay was known to be working at 0426 hours0.00493 days <br />0.118 hours <br />7.043651e-4 weeks <br />1.62093e-4 months <br /> on the day of the trip and on the previous day. On those two occasions, the 67 relay tripped and caueed the 86 GA relay to pick up, but as designed, the 04X relay prevented Lee "6C" from tripping off line. An investigation is still underway to determine the cause of its malfunction. The cause of the 67 relay trip is unknown and is being investigated also. This information 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. Both Lee "6C" and Lee "5C" became ready for start at about the same time, and it was decided to use Lee "6C" to supply power to the Oconee standby buses again, and to use Lee "5C" as a backup.

The eleven protective relays that are normally blocked in this mode by the 04X relay were manually blocked to prevent recurrence. The Lee "6C" gas turbine was placed on line at 1051 and both Oconec standby buses were reenergized by 1057.

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• JP0/JCP Saptember 27, 1983 Oconee Unit 3 returned to 100 percent full power at 1240 hours0.0144 days <br />0.344 hours <br />0.00205 weeks <br />4.7182e-4 months <br /> while Unit 1

,e continued reducing power to 90 percent full power for unrelated maintenance.

Unit 1 returned to 100 percent full power at 1705 hours0.0197 days <br />0.474 hours <br />0.00282 weeks <br />6.487525e-4 months <br />.

While both Keowee units were out of service and the standby buses were not energized form Lee, power was always available from the normal Duke Power Company transmission system to the,230KV switchyard via at least two 230KV transmission lines on separate towers. During this incident both the Lee "4C" and Lee "5C" gas turbines were available and could have energized the standby

-buses within one hour. Also,~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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