05000298/LER-1982-010, Forwards LER 82-010/03L-0.Detailed Event Analysis Submitted

Forwards LER 82-010/03L-0.Detailed Event Analysis Submitted

ML20053E836
Person / Time
Site:	Cooper
Issue date:	06/01/1982
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20053E837	List: 05000298/LER-1982-010, Forwards LER 82-010/03L-0.Detailed Event Analysis Submitted 05000298/LER-1982-010-03, /03L-0:on 820517,diesel Generator 1 & Output Breaker Tripped Shortly After Starting.Caused by Open Contact of Potential Transformer Disconnect Switch Interrupting Voltage to Overcurrent Relay Restraining Coil
References
CNSS820297, NUDOCS 8206100140
Download: ML20053E836 (2)

LER-1982-010, Forwards LER 82-010/03L-0.Detailed Event Analysis Submitted

Event date:
Report date:
2981982010R00 - NRC Website

text

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COOPER NUCLEAR STATloN Nebraska Public Power District

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CNSS820297 June 1, 1982

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UJH 41982 Mr. John T. Collins, Regional Administrator U.S. Nuclear Regulatory Commission Region IV W h2W'MN###

611 Ryan Plaza Drive 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 May 17, 1982. A licensee event report form is also enclosed.

Report No.:

50-298-82-10 Report Date:

June 1, 1982 Occurrence Date: May 17, 1982 Facility:

Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which resulted in not meeting a limiting condition for operation established in Table 3.9.B.4 of the Technical Specifi-cations.

Conditions Prior to Occurrence:

The reactor was operating at a steady state power level of approx-imately 827. of rated power.

Description of Occurrence:

During normal operation while performing Diesel Generator Oper-ability Test, the Diesel Generator #1 and its output breaker tripped.

Designation of Apparent Cause of Occurrence:

The apparent cause of this occurrence has been attributed to the potential transformer (PT) disconnect switch. One of its contacts apparently opened, interrupting voltage to the overcurrent relay restraining coil which tripped the diesel and its output breaker.

'@t 8206100140 820601 yDRADOCK 05000298 PDR 1

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Mr. John T. Collins June 1, 1982 Page 2.

Analysis of Occurrence:

There are two Emergency Diesel Generators which supply vital power in the event of a loss of offsite power.

Each diesel generator is independent of the other. The potential transformer disconnect switch is mounted on a metal door inside the 4160V switchgear next to the diesel generator output breaker.

It is believed that an improperly closed PT door vibrated ajar and opened one contact of the PT disconnect switch. The door is believed to have been im-properly closed after the last diesel generator inspection. The overcurrent relay restraining coil must receive 120V AC from the PT when the generator is producing a current flow.

Since 120V AC to the restraining coil was lost the relay operated and tripped the diesel and its output breaker.

Operability of the Diesel Generator #2 was immediately verified.

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

Corrective Action

The PT disconnect switch contacts were inspected and adjusted.

PT doors were properly closed and Diesel Generator #1 retested. The diesel generator was returned to service within 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />. The PT cabinet was labeled with a precaution to securely close the door to prevent its inadvertent opening.

Sincerely, jI

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f L. C. Lessor Station Superintendent Cooper Nuclear Station LCL:cg Attach.