05000298/LER-1979-015, Forwards LER 79-015/03X-1

Forwards LER 79-015/03X-1

ML19275A140
Person / Time
Site:	Cooper
Issue date:	08/01/1979
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19275A141	List: 05000298/LER-1979-015, Forwards LER 79-015/03X-1 05000298/LER-1979-015-03, /03X-1 on 790525:breaker 1AS Failed to Close Automatically After Reactor Scrammed.Caused by Improper Operations of Switch 52 in Breaker 1AN.Breaker 1FA Failed to Trip.Caused by Misaligned Trip Coil & Armature
References
CNSS790400, NUDOCS 7908310436
Download: ML19275A140 (3)

LER-1979-015, Forwards LER 79-015/03X-1

Event date:
Report date:
2981979015R00 - NRC Website

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Nebraska Publ.ic Power D. tr. t is ic TeLemo~c m.2s-3.u CNSS79G400 August 1, 1979 Mr. K. V. Seyfrit U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurrence that was discovered on >by 25, 1979. A licensee event report form is also enclosed. This revised report indicates changes in designation of apparent cause of occurrence and corrective action for breaker 1FA.

Report No.:

50-298-79-15-1 Report Date:

August 1, 1979 Occurrence Date: May 25, 1979 Facility:

Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which lead to operation in a degraded mode permitted by a limiting condition for operation established in paragraph 3.9.A.1 of the Technical Specifications.

Conditions Prior to Occurrence:

Steady state power operation at 290 MWe.

Event occurred immed-iately after the reactor scrammed.

Description of Occurrence:

When the reactor scra==ed, breaker lAS failed to close automat-ically.

Breaker lAS is the feeder breaker from the startup trans-former.

Secondly, breaker 1FA failed to trip automatically when bus IF was energized from the emergency transfor=cr.

Breaker 1FA is one of two breakers in series connecting the 4160V bus IF to the 4160V bus lA.

Breaker 1FA also failed to trip from the control room when the control switch was operated to TRIP.

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Mr. K. V. Seyfrit August 1, 1979 Page 2.

Designation of Apparent Cause of Occurrence:

It is believed that breaker lAS failed to close automatically because the auxiliary switch 52, located in breaker lAN, failed to close its contact when lAN opened due to the main generator trip.

When breaker lAN trips, its auxiliary switch 52 is returned to its nor=al position by a spring.

This spring, a part of the auxiliary switch, apparently failed to close the switch contacts.

On July 28, 1979, breaker 1FA was removed, inspected and tested under supervision of the manufacturer's engineers. A series of bench tests revealed that breaker 1FA failure to trip was caused by misalignment of the trip coil rather than by the contact of the position switch 52H not being closed as reported on June 23, 1979.

The problem did not become evident when breaker 1FA was operated in the test position.

Breakers lAS and 1FA are GE Magna Blast Type AMH 4.76-250.

Analysis of Occurrence:

During normal operation when the generator is connected to the 345 KV system, the 4160V bus LA is energized from the normal trans-former via breaker lAN. When the generator trips breaker lAN trips, and breaker LAS closes automatically and energizes the 4160V bus lA from the startup transformer.

Since breaker LAS failed to close, the 4160V bus IF was automatically energized from the emergency transformer.

Breaker lAS was then closed by the manual control switch.

Diesel Generator #1, the third source of power to the 4160V bus IF, started automatically and was operable. However, the diesel gen-erator did not energize bus IF due to the bus being energized by the emergency transformer.

Breaker IFA is in series with the breaker lAF.

Both breakers open on loss of voltage to bus IF.

Either breaker then isolates the emergency bus IF from bus lA.

Failure of breaker 1FA to trip did not affect operation of the emergency bus IF because lAF opened.

This occurrence presented no adverse consequences from the stand-point of public health and safety.

2035 289

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Mr. K. V. Seyfrit August 1, 1979 Page 3.

Corrective Action; The breaker manufacturer (GE) has been contactec in regards to the evaluation of the problem with breaker lAS.

The 3xisting auxiliary switch 52 was cycled, cleaned and tested satisfactc-ily. Further action will depend on the manufacturer's recommendaticas.

The trip coil support for breaker 1FA was readjusted to obtain the recommended trip armature travel as specified by the manufacturer.

The trip coil and the trip armature were aligned. Breaker 1FA was given a series of closing and tripping tests and correct operation verified.

The failure to trip which occurred on breaker 1FA has never been experienced on the remaining 51 similar breakers. Tripping of breaker 1FA will be verified again in about 8 weeks.

If satis-factory, no other further cecrective action is planned.

Sincerely, L. C. Lessor Station Superintendent Cooper Nuclear Station [Ohj [9O LCL:cg Attach.