ML19291C270

RO 50-219/78-03/3L-0:on 780214,startup Transformer Lockout 865A Alarm Annunciated in Control Room.Caused by Fault in Cable.Cable Standoffs Inspected,Cleaned & Varnished. Evaluation Being Performed on Cable

ML19291C270
Person / Time
Site:	Oyster Creek
Issue date:	03/15/1978
From:	JERSEY CENTRAL POWER & LIGHT CO.
To:
Shared Package
ML19291C260	List: ML19291C259 ML19291C264 ML19291C266 ML19291C270 ML19291C277 ML19291C282 ML19291C283
References
NUDOCS 8001230254
Download: ML19291C270 (3)

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ATI; m E E V Page 1 of 3 OYSTER CREEK i;UCLEAR GEtiEU.TitJG STATIOri Forked River, tiew Jersey Oc731 Licensee Event Report Reportable Occurrence tio. 50-219/78-03/3L-0 Report Date March 15, 1978 Occurrence Date February 14, 197'8 Identification of Occurrence Trip of startup transformer bank 5 caused the auxiliary power system to be operable in a degraded mode. This event is considerec to be a reportable occurrence as defined in the Technical Specificatiens, paragraph 6.9.2.b.2.

Conditions Prior to Occurrence The major plant parameters at the time of the occurrence were:

Power: Reactor, 1844 MWt Electric, 647 MWe 4

Flow: Recirculation, 14.6 x 10 gpm

• Feedwater, 6.895 x 106 lb/hr Stack Gas: 4.05 x 10" uci/sec Description of Occurrence On February 14, 1978, at approximately 1130 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.29965e-4 months <br />, the "startup transformer lockout 86SA" alarm annunciated in the station control room. A burn hole was detected in the cable bus duct. Further investigation revealed that the tap off of bank 5 to dilution main breaker had an insulation failure between B phase and ground at the support for the splice connector.

Apparent Cause of Occurrence The cause of the occurrence was attributed to a fault in the cable.

Analysis of Occurrence The normal auxiliary power supply for the plant is provided by a transformer directly connected to the 24 KV generator. Startup power and standby auxiliary power is provided by two transformers supplied f rom separate 34.5 KV buses in the switchyard. The buses are connected through a circuit breaker which will open automatically if either _ bus is faulted. Therefore, it is unlikely that pcwer line catcces or equjpmen; failures will cause an interruption to the station's standby auxiliary power. Either of the two

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ATIAGEir V Page 2 of 3 Renartable Occurrence io. 50-219/73-03/?L-0 Page 2 March 15,1973 startup transformers is more than arple to carry the energency au>;ilicry power Icad. The safety tignificance of this event is considered to be minir.al since during this period redundant power supply from bank 6 was available.

The auxiliary pc..er system was still considered operable with the loss of bank 5 but in a degraded mode.

Corrective Action The insulation failure between B phase and ground at the support for the splice connector was taped according to normal taping procedure. Cable stand-offs affected by the fault were cleaned and varnished and all standoffs in -

the area were inspected. An evaluation is being performed on the cable to determine whether further action is required.

Failure Data it is suspected that a similar undetected fault in this cable was responsible for the 1-C bus trip which occurred on July 28, 1977. (See Reportchle Occurrence tio. 50-219/77-17/3L.)

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A'I"lACH'E.'r V Page 3 of 3 RESPCr!SE 'IO ENCIDS~.3E CfESTIO::S REPORTABLE OCCURRC C 53-219/78-3 Secticn A of Enclosure Qaestions is pertinen: since this event involved only one Startup Transformer.

RESPONSE

A.1 'Iko circuits are available; one was lost.

A.2 Cause was ground fault on B phase of cable bus.

A.3 Degradation of cable bus was more advanced in the Bank 5 Cable Bus. .

A.4 No voltage excursions are relevant to this event.

A.5 lb frequency excursions are relevant to this event.

A.6 hhile repairs were being made the Bank 5 cable bus was out of service appw.. 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

A.7 Ihte of Event: 2/14/78 1792 216