ML20064H168

/03L-0 on 780629:during Steady State Oper Motor Control Ctr 893 Lost Voltage Because B Uninterruptible Pwr Supply (UP5) Tripped Due to Blown Inverter Leg Fuse.Failed Components Replaced & Operability Test Performed

ML20064H168
Person / Time
Site:	Vermont Yankee
Issue date:	07/25/1978
From:	Conway W VERMONT YANKEE NUCLEAR POWER CORP.
To:
Shared Package
ML20064H162	List: ML20064H160 ML20064H168
References
LER-78-019-03L, LER-78-19-3L, NUDOCS 7812180194
Download: ML20064H168 (2)

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, EVE'IT DESCRIPTICN AND PR03A31.E CONSEOUI'TCES During steady state operation, Control Room personnel reported a loss of voltage to Motor Control Cancer 393. This MCC powers the "3" l LPCI injection valves and the "3" recirculation system discharge and '

discharge bypass valves. Upon imrestigation, it was found that the "3" Uninterruptible Power Supply (UPS) had tripped because of a blown inverter leg fuse. This condition is contrary to the requirements of Technical Specifications Section 3.10.3.4. During maintenance, alter-nate testing in accordance with Tecnnical Specifications Section 4.5.A.4 vas initiated and completed. In addition, the alternate power supply

, (maintenance feeder) was energited to provide power to MCC 893. The total elapsed time period for the loss of operability of the UPS-13 unit was approximately 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />. During this time period, the redundant _"A" UPS System, both core spray subsystems, the containment cooling subsys-tems, the "A" LPCI subsystem and both diesel generators were operable.

Based upon the preceding equipment availability, it is concluded that there were no adverse consequences to the public healen or safety as a result of this event. Similar events were reported as RO 76-34/3L and RO 78-12/3L.

CAUSE DESCRIPTION AND COPSICTI7E ACTIONS An Exide Power System, 250 K7A Uninterruptible Power Supply, had tripped because of a blown inverter leg fuse (2A1972). Troubleshooting

( of the unit determined that the cause of the fuse failure was attribu-( ~

table to the malfunctioning of a 2A13A4 gate interface logic module and a 2A13A15 AC protection logic module. The corrective action for this e event was to replace failed components in kind and perform satisfactory operability testing.

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