ML20054F846

Ro:On 820605,one of Two Undervoltage Relays Which Monitor Reserve Auxiliary Transformer Tripped,Causing Load Shedding of Essential Busses 1 & 2.Caused by Procedural Inadequacy

ML20054F846
Person / Time
Site:	Fort Saint Vrain
Issue date:	06/09/1982
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Kuzmycz G NRC
References
PPC-82-1175, NUDOCS 8206180002
Download: ML20054F846 (3)

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),id , d 16805 Weld County Road 191/2, Platteville, Colorado 80651-9298 wraa a June 9,1982 Fort St. Vrain Unit No. 1 PPC-82-1175 fir. George Kuzmycz Nuclear Regulatory Conmission 7920 Norfolk Avenue Bethesda, Maryland 20034

Dear Mr. Kuzmycz:

As per your request, attached is information concerning the manual t, cram taken June 5,1982, due to an undervoltage relay trip in the plant elec-trical system.

If you have any further questions, please contact Ed Hill.

Very truly yours ,

~ WkM Y /%

Don Warembourg Manager, Nuclear Production DW/cls Attachment l

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On June 5, at 1550 hours0.0179 days <br />0.431 hours <br />0.00256 weeks <br />5.89775e-4 months <br />, with the reactor at approximately 13% power, one of two undervoltage relays, which monitor two phases of the 4KV side of

- the reserve auxiliary transformer, tripped, causing load shedding of the 480V essential busses 1, 2, and 3. Both undervoltage relays have to trip to cause the 4KV feed breaker to trip, thus, it remained closed and 4KV power equipment ("B" boiler feedpump, A and B condensate pumps, A and B circulator pumps), except the 480V busses, remained operating / operable.

The purpose of the relays is to detect low voltage from the 4KV (i.e. ,

4 loss of electrical power or phase loss) coincidental with a turbine trip

and shed the load from the 480V busses in order to ensure the diesel generators close in on a dead bus.

The reactor operator manually scrammed the reactor, and the diesel gener-ator units A and B automatically started and closed in to the dead 480V busses. l A diesel generator set picked un 480V bus 1 and 2 as it was

the first up-to-speed and IB diesel generator set picked up bus 3. The programmed automatic sequencer for the diesel generators started un es-sential equipment as designed, and no problems were encountered. The buffer / bearing water upset tripped three of four helium circulators and 1

resulted in a small amount of activity being released to the Reactor a Building; however, MPC limits were not exceeded. Activity levels had

decayed to background levels by 2240 hours0.0259 days <br />0.622 hours <br />0.0037 weeks <br />8.5232e-4 months <br />.

1 Recovery actions were started immediately, and the 480V busses and diesel generator units were paralleled to the 4KV at 1810 hours0.0209 days <br />0.503 hours <br />0.00299 weeks <br />6.88705e-4 months <br />. The elec-trical system was restored to normal at 2030 hours0.0235 days <br />0.564 hours <br />0.00336 weeks <br />7.72415e-4 months <br /> and plant recovery operations continued as expected. Subsequent investigation revealed a PFC relay department procedural inadequacy in calibrating the relay in q ues tion. A followup report will be submitted per the reoorting re-quirements of Fort St. Vrain Technical Specification AC 7.5.2(b)3.

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