ML19312C197

Abnormal Occurrence Rept AO-269/75-13:on 751108,Keowee Hydro Unit 1 Failed to Autostart.Caused by Electrical Malfunction of Breaker.Malfunctioning Generator Supply Breaker Removed, Cleaned & Repaired.Keowee Unit 2 Tested & Returned to Svc

ML19312C197
Person / Time
Site:	Oconee
Issue date:	11/21/1975
From:	DUKE POWER CO.
To:
Shared Package
ML19312C193	List: ML19312C192 ML19312C197
References
NUDOCS 7912100683
Download: ML19312C197 (2)

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Report No.: A0-269/75-13 Report Date: November 21, 1975 eak:*: b '" ",14--21-7(

Occurrence Date: November 8, 1975 Facility: Oconee Units 1,2,3, Seneca, South Carolina Identification of Occurrence: Failure of Keowee Hydro Station Unit 2 to autostart Conditions Prior to Occurrence: All units in power operation Description of Occurrence:

On November 8, 1975, while all Oconee units were in power operation, an attempt was made to start Keowee Hydro Unit 2 from the Oconee Control Room for system load. Due to an electrical malfunction of the unit's generator supply breaker, Keowee Unit 2 failed to start. The Keowee Unit I was immediately connected to the underground feeder cable while maintenance action was performed on Keowee Unit 2. Keowee Unit 2 was restored to an operable status in approximately seven and a half hours.

Apoorent Cause of Occurrence:

Investigation revealed that there was mechanical binding in the Keowee Unit 2 generator supply breaker linkage from the closing coil to the auxiliary contacts. This binding apparently prevented the breaker from electrically closing and making the electrical connections necessary to remotely start the unit. Keowee Unit 2 was last automatically started at 1300 on November 6, 1973.

Analysis of Occurrence:

This incident resulted in one of two redundant emergency power sources being inoperable for approximately seven and one half hours. During this incident, Keowee Unit I was operable and would have been available to supply emergency power. Oconee Technical Specification 3.7.2(b) provides for a test or maintenance period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for one Keowee Unit, provided the remaining unit is connected to the underground feeder cable. Since the provisions of this Technical Specification were met, it is concluded that the health and safety of the public was noe. affected.

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Corrective Action:

4 The generator supply breaker which malfunctioned was removed, cleaned, and repaired. After reinstallation of the breaker, Keowee Unit 2 was successfully tested and returned to service. Presently, preventative maintenance work is performed on the breakers at Keowee on an annual basis. It is felt that this maintenance schedule combined with the present surveillance of the Keowee Units through testing and normal operation provides a sufficient safety margin for the prevention or early discovery and correction of malfunctions of this type.

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