ML20062E658

/01T-0 on 781106:turbine Runback Resulted from Safeguards Bus Tie Breaker Trip.Westinghouse Model CV-7 Undervoltage Relay on Tie Breaker Tripped Causing Breaker to Open.No Line Voltage Surges Detected

ML20062E658
Person / Time
Site:	Point Beach
Issue date:	11/17/1978
From:	Burstein S WISCONSIN ELECTRIC POWER CO.
To:
References
LER-78-016-01T, LER-78-16-1T, NUDOCS 7812110189
Download: ML20062E658 (2)

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U.S. NUCLEAR REGULAT C N NRC h0ZM 3d (7 77)

LICENSEE EVENT REPORT g g @, ,4 L D 'urROLstOCiel l l l l l l@ (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION l 0 l 8i 9l l W LICENSEEl I l PCODE l B l H l 1 l@l 0 l 0 l LICENSE 14 15

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CON'T I0l1l 7 8 SOORC 60 l L }@l 0DOCKET 61 l 5 NUM8ER l 0 l 0 l 0 68l 2 59l 6 I6EVENT l@lDATE1l 110 l 6 I 7 REPORT 74 75 l 8 l@lDATE 1 l 1l 80 1 l 7 l 7 l 8 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h Io l2l lDuring normal operation at 1643 hours0.019 days <br />0.456 hours <br />0.00272 weeks <br />6.251615e-4 months <br />, 11-6-78, a turbine runback re- l i o ,3, gsulted from a safeguards bus tie breaker trip. One pressurizer heater j This, along with i o i4, gbackup group was lost when the tie breaker tripped.

l g gthe control rods automatically stepping in and reducing reactor power l 10 ts i I during the turbine runback resulted in reactor coolant system pressure I

ibrlefly dropping to 2193 psia. T.S. 15.3.1.A.4.A.2 states that pressurel i o ig i imay not drop below 2220 psia when normal < perating pressure is 2250 psiat

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35 36 J7 40 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS lijo;lA Westiaghouse Model CV-7 undervoltage relay on the tie breaker tricoed l ii iiil causing the breaker to open. Careful examination of the undervoltace 1 i ,g grelay, tie breaker, af fected bus , and other protection relays disclosed I i,i3i jno abnormalities. No line voltage surges were detected. The breaker I i,i,ilwas closed, and normal operation was resumed. 80 I

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78121101ft

ATTACHMENT TO LER NO. 78-016/0lT-0 Wisconsin Electric Power Company Point Beach Nuclear Plant Unit 1 Docket No. 50-266 During normal full power operation (495 MWe) at 1643 hours0.019 days <br />0.456 hours <br />0.00272 weeks <br />6.251615e-4 months <br /> on November 6, 1978, the tie breaker (lA52-57) between lA03 and 1A05 4160 V engineered safeguards buses tripped.

This resulted in a turbine runback due to loss of DC power to the control rod position indication (RPI) cabinets. The runback was stopped at 440 MWe when the 3D emergency Diesel generator automatically phased onto the 1A05 bus following the bus's undervoltage condition and power was restored to the RPI cabinets. One pressurizer heater backup group

( (0.2 MWe) was lost when the tie breaker tripped. This, along with the control rods automatically stepping in and reducing reactor power during the turbine runback, resulted in reactor coolant system pressure briefly dropping to a low of 2193 psia at 1647 hours0.0191 days <br />0.458 hours <br />0.00272 weeks <br />6.266835e-4 months <br />. Limiting Condition for Operation, Technical Specification 15.3.1.A.4.A.2 states that pressure may not drop below 2220 psia when normal operacing pressure is 2250 psia.

Plant conditions were returned to normal and the unit was returned to full power by 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br />.

Subsequent to the event the breaker was carefully examined for defects but none were found. A check of the affected bus and other protection relays disclosed no abnormalities. Monitoring of the 345 KV system at the time l of the incident did not disclose any undue voltage surges.

t It is therefore presumed that the opening of tie breaker lA52-57 precipitated this event; however, a determination cannot be made based upon available evidence as to why this breaker spuriously tripped at that time.

Per normal plant practice a ccpy of this Licensee Event Report will be routed to operating personnel to inform them of this unexplained breaker operation. -

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