ML19256G118

Final Rept on Field Relay Coil Failures.Field Relay Coils Replaced & Generators Back in Svc

ML19256G118
Person / Time
Site:	Sequoyah
Issue date:	12/18/1979
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19256G116	List: ML19256G115 ML19256G118
References
NUDOCS 7912270476
Download: ML19256G118 (2)

Text

ENCLOSURE SEQUOYAH NLCLEAR PLANT UNITS 1 AhD 2 DIESEL GENERATOR FIELD RELAY COIL (K1) FAILURES NCR 13P 10 CFR 50.55(e)

FINAL REPORT Description of Deficiency The deficiency, which arises f rom the f ailure of the field relay coil, is that the diesel generator starts and comes up to speed, but has no generator output. It was discovered by operating employees during routine operations of the diesel generator units. The diesel generators have completed pre-operational testing.

Failure of the field relay maintains the field of the generator in an elec-trically shorted condition throughout the start sequence, and the generator is incapable of any voltage buildup or output. Therefore, loss of the K1 coil causes a part of the emergency onsite electrical capacity to be unavailable.

TVA and Morris-Knudsen, the diesel generator vendor, believe that the two failures of the field relay coil (Kl) are randem failures. The failed relay is a latching device and remains in the operated mode until the voltage is applied to the reset coil.

T7A has experienced failures of these fielc relay coils only at Sequoyah huclear 'lant. The ccmpanion plant to Sequoyah, Matts Bar Suclear Plant, is equi. ped with the same model relay. However, the circuitry at Watts Bar Nuclear Plant is different in that the generator field is not normally kept in an electrically shorted condition as at Sequoyah. Hence, failure of the K1 relay at Watts Ear Nuclear Plant will not lead to loss of generator output.

Safety Implications If this deficiency had remained uncorrected, the possibility exists that a K1 field relay coil might have failed concurrently with an accident because of other causes. If onsite emergency electrical power was required to mitigate the effects of that accident, sufficient power may not have been available because of failure of the field relay coil. Thus, the safety of the plant would have been jeopardized by lack of suf ficient electrical power to supply equipment required to support shutdown to a safe condition.

Corrective Action The field relay coils that failed have been replaced with new field relay coils from the same manufacturer (ITE Gould). The diesel generators which experienced f ailed field relay coils are all back in service at Sequoyah Nuclear Plant. The relays replacing the latching relay are magnetically held in the operating position and return to the deenergized state after removal of power from the coil.

7912270 1644 320

Power Syste:as Division of Morris-Knudsen has designed a start circuit modification which aliminates an electrical short of the generator field during the start seqtence. This will permit the generator to produce output in spite of failures in the field relay coil. The field of the generator will be flashed by the operation of a separate magnetically held relay.

The circuit modification outlined above will be installed in all four emergency diesel generators at Sequoyah before unit 1 fuel loading.

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