PNO-IV-85-064A, on 851212,offsite Power Loss Occurred During Electrical Storm When Switchyard Breakers Tripped Because of Ground Current from Startup Transformers.Trip Relays Reset from 1,200 to 2,400 Amps

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PNO-IV-85-064A:on 851212,offsite Power Loss Occurred During Electrical Storm When Switchyard Breakers Tripped Because of Ground Current from Startup Transformers.Trip Relays Reset from 1,200 to 2,400 Amps
ML20138P069
Person / Time
Site: Waterford Entergy icon.png
Issue date: 12/18/1985
From: Constable G
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:
References
PNO-IV-85-064A, PNO-IV-85-64A, NUDOCS 8512240273
Download: ML20138P069 (2)
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December 18,,1985 b /* PRELIMINARY NOTIFICATION OF' EVENT OR UNUSUAL OCCURRENCE -- PNO-IV-85-64A This preliminary notification constitutes EARLY notice of events of POSSIBLE

. safety or public interest significance. It is an update of a preliminary.

- notification issued on t rember 13, 1985. The information is as initially

' received without verification or. evaluation, and is basically all that is known by the Region IV staff on this date.

FACILITY: Licensee Emergency Classification:

Louisiana-Power' & Light Cornpany Notification of Unusual Event Waterford 3 Alert i ft, Louisiana Site Area Emergency Docket No. 50-382 General Emergency X Not Applicable

SUBJECT:

LOSS OF 0FFSITE POWER AT WATERFORD 3--UPDATE A preliminary notification on December 13, 1985, indicated all offsite power at Waterford 3 Steam Electric Station was lost for approximately one-half hour beginning at 7:26 p.n. CST on December 12, 1985, during a severe electrical storm.

Further investigation by the licensee indicates that power was not lost to either the east or west bus in the plant switchyard. However, offsite power to Waterford 3 was lost as a result of the tripping of switchyard breakers.

Emergency diesel generators started and functioned as designed.

Although offsite power was not restored for. approximately one-half hour, this length of time was discretionary in that power could have been restored much sooner if needed. The licensee determined that a fault associated with a lightning strike occurred at approximately 7:23 p.m. CST on the Waterford-Little Gypsy 1 line to the switchyard. This caused two breakers at each end of the line to open to cicar the fault. The bus side breaker at both Waterford and Little Gypsy automatically reclosed to restore the transmission (cont.onnextpage)

CONTACT: G. L. Constable, FTS 728-8151 DISTRIBUTION:

MAIL:

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Chairman Palladino. ED0 IE NMSS

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Com. Bernthal ELD AE0D FAX:

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PDR LICENSEE:

Regional Offices (ReactorLicensee)

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line to carry. load..;At'approximately 7:26 p.m., the Southern Control dispatcher attempted to close, by supervisory control, the tie breaker between the two switchyard buses which had opened to clear the fault. This breaker then faulted , internally (B phase to'-ground) causing additional switchyard breakers to'open.

At about this same time, the four breakers supplying power to Waterford 3 tripped. The licensee has determined that the loss of offsite power to Waterford was caused by the-startup transformers generating a ground current due to the phase to ground fault occurring in the Waterford switchyard. This resulted in solid state phase comparison relays sending trip signals to the four supply breakers. The licensee believes that if the plant had been on line, the plant generator would have contributed sufficient fault current

' througn the lines to prevent the breaker trips. These trip relays were found to be set at 1200 amperes ratner than the intended 1500 ampere setting. These relays have now been set at 2400 amperes to prevent recurrence of this event.

h The NRC regional end headquarters staff are following this investigation.

No press release has been made nor has redia interest been identified.

The state of Louisiana has been informed, k

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