ML19352A094

LER 77-004/01T-0:on 770318,electrical Fault Occurred on 1C Bus & Subsequent Trip of 1C Breaker Left Bus de-energized. Caused by Phase Leads Being Grounded Between 1C Bus & Diesel Generator Breaker.Faulty Cable Replaced

ML19352A094
Person / Time
Site:	Oyster Creek
Issue date:	03/30/1977
From:	Ross D JERSEY CENTRAL POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
LER-77-004-01T, LER-77-4-1T, NUDOCS 8103040393
Download: ML19352A094 (4)

Text

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[5((j l On Friday, March 18, 1977, at 3:15 PM, an electrical fault occurred on 1C bus and 7 il if t-

@l a subsequent trip of the IC breaker left the bus de-energized in violation of the 7 r9 i,

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@b l the Diesel Generator #1 (DG #1) breaker. The DG #1 cable is an extension of the IC 7 89 y

@ [_ bus as there is no breaker until this cable reaches the diesel generator breaker D9 i.

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CAUSE DESCRIPTION (continued) (50-219/77-4-IT) __ _

(DG #1) at the diesel generator building.

Preparations to place the plant in a cold shutdown condition were begun at 3:30 PM. Load reduction began at 4:23 PM but was terminated at 6:30 PM af ter all phase leads of the affected cable were disconnected from the IC bus and the bus was re-energized.

Three cables (i.e., the two phase "C" leads and one phase "B" lead,all within the same conduit) for DG #1 were replaced and high potential tested.

The IC bus was temporarily removed from service to allow the DG #1 cables to be reconnected to the bus.

The faulty cable will be sent to a testing laboratory for analysis to determine 4 the failure mode. A cable replacement and preventive maintenance testing schedule has been established and will be implemented during the 1977 refueling outage.

Failure Data Cable General Electric Company Vulkene - insulated and shielded

1. SI-58064 Rated at 5 KV Reportable Occurrence Report No. 75-9 This occurrence resulted in the re-placement of four of the six tie cables between DG #1 breaker and the IC bus.

It should be noted that the cable failure in this report (77-4) occurred in one of the two cables that was not replaced after the (75-9) occurrence.

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OYSTER CREEK NUCLEAR GENERATING STATION Forked River, New Jersey 08731 Licensee Event Report Reportable Occurrence No. 50-219/77-4-IT Report Date March 30, 1977 Occurrence Date March 18, 1977 Identification of Occurrence Violation of the Technical Specifications, paragraph 3 7.A.I.a, when an electrical fault occurred on IC bus and a subsequent trip of IC breaker left the bus de-energized. This event is considered to be a reportable occurrence as defined in the Technical Specifications, paragraph 6.9.2.a.(2).

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

Power: Reactor, 1356 MWt Generator, 462 MVe (g)

Flow: Feedwater, 4.9 x 10 6 lb/hr 4

Recirculation, 13.5 x 10 gpm Stack Gas: 10,600 pci/sec Description of Occurrence ,

On Friday, March 18, 1977, at 1515, breaker IC tripped. Concurrently, alarms "DG1 Trouble" and "DG1 Lockout Relay Trip" were received. A half scram was received due to the loss of Reactor Protection System No. I which at the time of the occurrence was being powered by VMCC 1A2 through the MG set. Power to the reactor protection system was re-established via VMCC IB2 and the 25 KVA

. transformer. Subsequently, IC bus was isolated and the unit substations lAI, lA2, and 1A3 were re-energized via the cross-tie breakers to unit substations IB1, 1B2, and 1B3 Reactor Protection System No. I power feed was then transferred back to the MG set.

Apparent Cause of Occurrence The trip of IC breaker was discovered to be caused by a fault on the cable One of the tie between 1C bus and the Diesel Generator #1 (DG #1) breaker.*

"C" phase leads was discovered grounded at a point between the IC bus and the DG #1 breaker.

• Note: The DG #1 cable is an extension of the C bus as there is no breaker until this cable reaches the DG #1 breaker at the diesel generator building.

._ _ _ . . _ ~ . . , , , _ , _ . . _ . _ _ . _ _ . ,__ . . . _ _ _

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. s Reportable Occurrence No. 50-219/77-4-lT' Page 2 March 30, 1977 Analysis of Occurrence Th b ! 5 O The unavailability of either IC or ID bus has been previously analyzed in "ECCS Modification Core Spray Electrical Crossconnect" report, dated June 24, 1975, submitted to the NRC in support of issuance of Operating License Amendment No. 8. The net ef fect of the. modification and its impact on this particular event (loss of either 1C or ID bus) is that both core spray systems are still capable of establishing rated flow because of the independence and redundancy of the AC power supplies. Thus, there is no additional safety significance associated with this event beyond that already analyzed.

Corrective Action After assessing conditions, preparations to place the reactor in a cold shut down condition were initiated at 3:30 PM. Load reduction began at 4:23 PM.

The IC bus was re-energized after all phase leads of the affected cable had been disconnected from the bus. Associated unit substations were then energized from the IC bus. The reactor shutdown was terminated at 6:33 PM following restoration of the IC bus.

Three cables (i.e., the grounded cable and two additional cables for DG #1, all within the same conduit) were replaced and high potential tested. Bus IC was temporarily removed from service, after consultation and concurrence by the NRC, to allow the replacement cables to be reconnected to IC bus. The faulty cable will be sent to a testing facility for analysis to determine its failure mode. In addition, a cable replacement and preventive maintenance testing schedule has been established and will be implemented during the 1977 spring refueling outage.

Failure Data Cable General Electric Company Vulkene - insulated and shielded

1. 51-58064

! Rated at 5 KV i

Abnormal Occurrence Report No. 75-9 This occurrm,ce resulted in the replacement of four of the six tie cables between DG #1 and 1C bus, it is noted that the cable failure in this report (R0 No. 50-219/77-4-lT) occurred in one of the two remaining cables.

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