05000338/LER-1981-020-03, /03L-0:on 810402,emergency Bus 4160-volt/480-volt Transformer 1H1 Failed.Caused by Internal Short on Phase a of Transformer.Transformer Replaced

/03L-0:on 810402,emergency Bus 4160-volt/480-volt Transformer 1H1 Failed.Caused by Internal Short on Phase a of Transformer.Transformer Replaced

ML20003G212
Person / Time
Site:	North Anna
Issue date:	04/22/1981
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20003G211	List: 05000338/LER-1981-020, Forwards LER 81-020/03L-0 05000338/LER-1981-020-03, /03L-0:on 810402,emergency Bus 4160-volt/480-volt Transformer 1H1 Failed.Caused by Internal Short on Phase a of Transformer.Transformer Replaced
References
LER-81-020-03L-01, LER-81-20-3L-1, NUDOCS 8104280477
Download: ML20003G212 (2)

LER-1981-020, /03L-0:on 810402,emergency Bus 4160-volt/480-volt Transformer 1H1 Failed.Caused by Internal Short on Phase a of Transformer.Transformer Replaced

Event date:
Report date:
3381981020R03 - NRC Website

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v U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT

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(PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION)

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DOCKET NUMBER EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES (10)

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On April 2, 1981, while in Mode 4, the emergency bus 4160V/480V "1H1"

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transformer failed, thereby causing loss of all 480V loads and "A" Semi-Vital /

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Bus loads. Since a redundant emergency bus remained (1J) to carry all

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necessary safety related loads and the Unit was already in hot shut Town, the /

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health and safety of the public were not affected. This event is r" portable /

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pursuant to T.S. 6.9.1.9.b.

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SYSTEM

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SEQUENTIAL OCCURRENCE REPORT REVISION LER/R0 EVENT YEAR REPORT NO.

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ACTION FUTURE EFFECT SHUTDOWN ATTACHMENT NPRD-4 PRIME COMP. COMPONENT

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS (27)

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This event was caused by an internal short on A phase of the affected

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transformer. The reactor shutdown banks were tripped, the IH1 transformer

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isolated and action statement entered. The transformer was replaced,

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satisfactorily tested and returned to service within 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> of the

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incident.

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FACILITY METHOD OF STATUS

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OPERATOR OBSERVATION

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NRC USE ONLY

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F PREPARER W. R. CARTWRIGHT PHONE (703) 894-5151 18104260 fE

()

Virginia Electric and Power Company North Anna Power Station, Unit #1 Attachment: Page 1 of 1 Docket No. 50-338 Report No. LER 81-020/03L-0 Description of Twent On April 2, 1981, with Unit I in Mode 4 and Unit II at 100% power, "1H1" 4160V/480V transformers failed. This event caused an instantaneous overcurrent trip of breaker 15H8. Consequently, all 480 volt loads on "1H" and "1H1" busses were lost. The low voltage condition created by the fault was sensed by the undervoltage relay on breaker 25G1 which tripped 25G1 (in c-ne cycle) before the fault could be isolated by 15H8.

With the loss of "2G" (4160 volt) bus due to the tripping of 25G1 breaker, all circulating water pumps for Unit II were lost. Subsequently, the Unit II turbine was manually tripped because of' decreasing condenser vacuum thereby resulting in an automatic reactor trip on Unit II.

Probable Consequences of Occurrence Since a redundant emergency bus (IJ), with twc operable 480V busses,-

remained available throughout the event, the public health and safety were not affected.

Cause of Event

()

The affected transformers failed due to a primary to secondary short on "A" phase.

Immediate Corrective Action

Immediate actions included tripping the reactor, isolating the failed "1H1" transformer and entering the appropriate action statement.

Subsequent action included replacing the failed transformers, testing and returning it to service within 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> of the incident.

Scheduled Corrective Action No further action is required.

Actions Taken to Prevent Recurrence No further actions are required.

Generic Implications There are no generic implications associated with this event.