ML19329B909

RO NP-33-77-10:on 770610,while Providing Temporary Power to Essential Instrumentation Distribution Panel Y1 from Alternate Feed YAR06 to Replace Transter Switch Y1,inverter YV1 Tripped.Caused by Procedure Error.Fuse Replaced

ML19329B909
Person / Time
Site:	Davis Besse
Issue date:	07/05/1977
From:	Batch S, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19329B899	List: ML19329B898 ML19329B909
References
NUDOCS 8002060900
Download: ML19329B909 (2)

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caust otsc=ertion I Procedure error in ,t,he Maintenance Instruction used caused the trip of YVi g

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TOLEDO EDISON COMPANY DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION

, SUPPLEMENTAL INFORwATION FOR LER NP-33-77-10 DATE OF EVENT: June 10, 1977 FACILITY: Davis-B' esse Unit 1 IDENTIFICATION OF OCCURRENCE: Loss of SFAS Channel 1 due to loss of Y1.

Conditions Prior to occurrence: The plant was in Mode 5. Power: 5"r-0, 5'E-0 Description of Occurrence: At 0945 hours0.0109 days <br />0.263 hours <br />0.00156 weeks <br />3.595725e-4 months <br /> on June 10, 1977, initial arrangements were being made to replace a defective transfer switch SY101 in Essencial Instru-mentation Distribution Panel Yl. While providing temporary power to Y1 from alternate feed YAR06, the inverter YV1 tripped. Power on Y1 was lost and conse-quently, power to SFAS Channel 1 was lost placing us in Action Statement #9 of '

... Table.3.3-3.,, , , , _ _ . . . . . _ , _ . . .. .

Designation of Accarent Cause of occurrence: This occurrence has been determined to have been caused by a procedure error in the Maintenance Instruction used.

This switch cannot be replaced without first tripping Yl.

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Analvsis of occurrence: Since three out of the four SFAS channele were still operable and SFAS Channel I was tripped, the SFAS would operate if required.

Therefore, the health and safety of the public and station personnel was not threatened.

Corrective Action: All sources of power to Y1 were de-energized and the defec-tive switch replaced. The fuse was replaced and YV1 and Y1 were restored to normal by 1103 hours0.0128 days <br />0.306 hours <br />0.00182 weeks <br />4.196915e-4 months <br />. The Maintenance Instruction has been chanced to renove power from Y1 before replacing the transfer switch.

Failure Data: No previous similar events have occurred.

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