05000346/LER-1979-088-03, /03L-0:on 790807,supply Breaker for Essential Unit Substation Bus F1 Tripped de-energizing Bus.Caused by Electrical Fault in Baat Room Heater,Instituting Operation of Neutral Overcurrent Device

/03L-0:on 790807,supply Breaker for Essential Unit Substation Bus F1 Tripped de-energizing Bus.Caused by Electrical Fault in Baat Room Heater,Instituting Operation of Neutral Overcurrent Device

ML19207C054
Person / Time
Site:	Davis Besse
Issue date:	08/30/1979
From:	Naylor R TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19207C042	List: 05000346/LER-1979-088, Forwards LER 79-088/03L-0 05000346/LER-1979-088-03, /03L-0:on 790807,supply Breaker for Essential Unit Substation Bus F1 Tripped de-energizing Bus.Caused by Electrical Fault in Baat Room Heater,Instituting Operation of Neutral Overcurrent Device
References
33-79-102, LER-79-088-03L, LER-79-88-3L, NUDOCS 7909060377
Download: ML19207C054 (3)

LER-1979-088, /03L-0:on 790807,supply Breaker for Essential Unit Substation Bus F1 Tripped de-energizing Bus.Caused by Electrical Fault in Baat Room Heater,Instituting Operation of Neutral Overcurrent Device

Event date:
Report date:
3461979088R03 - NRC Website

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U. S. NUCLEAR REGULATORY COMMISSION NRC FORM 366 (7-77)

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On 8/5/79, at 0015 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> the supply breaker for essential unit substation bus "Fl" l

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While selectively reloading the bus to determine the location of the fault, l

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l the supply breaker acain tripped on overcurrent at 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br /> when the breaker supplv-j l ing the Boric Acid Addition Tank (BAAT) room heaters was reclosed. There was no danger.

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o a lThe redundant essential bus "E1" was operable.

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i i Statement. After re-entering the Action Statement at 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br />, the bus was re-1, [ 2 l l energized at 0625 hours0.00723 days <br />0.174 hours <br />0.00103 weeks <br />2.378125e-4 months <br /> on August 5, 1979, removing the unit from the Action Statement 4 l The problem with the BAAT room besters will be corrected under Maintenance Work Order l i 3 [il4l]79-2734. Ground fault protection on the individual 480 VAC MCCs will be installed.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POUER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-lC2 DATE OF EVENT: August 5, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Overcurrent fault tripping on the neutral of essen-tial unit substation bus "Fl" The unit was in Mode 1, with Power (MWT) = 2772, Conditions Prior to Occurrence:

and Load (Gross MWE) = 914 Description of Occurrence: On August 5, 1979, at 0015 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> essential unit substation bus "Fl" supply breaker tripped, de-energizing "Fl" bus.

This placed the unit in the Action Statement of Technical Specification 3.8.2.1 which requires all essential AC electrical busses operable in Modes 1, 2, 3, and 4.

The Action Statement requires the inoperable bus be re-energized within eight Sours or the unit be in hot standby within the next six hours.

"F1" bus uas stripped and re-energized at 0030 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />, removing the unit from the Action Statement.

The bus was selectively reloaded to determine the source of the f ault.

At 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br /> when operations personnel reclosed the boric acid addition tank (BAAT) room heaters supply breaker BR1315 on MCCF13, the c"ercurrent trip recurred.

This again placed the unit in the Action Statement of Technical Specification 3.8.2.1.

Bus "Fl" was re-energized at 0625 hours0.00723 days <br />0.174 hours <br />0.00103 weeks <br />2.378125e-4 months <br /> removing the unit f rom the Action Statement.

The breaker to the BAAT room heater, BF1315, was left de-energized and was tagged to prevent operation of the breaker until the fault was repaired.

Designation of Anparent Cause of Occurrence:

The cause of this occurrence was an electrical f ault in the BAAT room heater which caused tF neutral overcurrent device to operate and trip the supply breaker to "Fl" bus, de t rgizing "Fl" bus.

This occurred because there is no ground fault protection on the 480 V AC motor control centers (MCC). Any ground fault on the low voltage side of the unit substation will cause the neutral overcurrent device to actuate and trip the substation supply breaker. This condition was previously identified as a potential problem and Faci-lity Change Request (FCR)79-223 was written on June 24, 1979. This FCR would install ground fault protection at the MCC supply breakers to prevent loss of a substation due to a ground on downstream loads.

Analysis cf Occurrence:

There was no danger to the health and safety of the public or to station personnel.

The redundant essential bus "El" was operable throughout the occurrence.

"Fl" bus was de-energized for a period of 15 minutes at 0015 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> and for 5 minutes at 0620 hours0.00718 days <br />0.172 hours <br />0.00103 weeks <br />2.3591e-4 months <br />.

LER #79-088 cet.: ("? ^

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFORMATION FOR LER NP-33-79-102

Corrective Action

On August 5, 1979, Maintenance Uork Order (MWO) 79-2734 was written to correct the problem with the BAAT room beaters.

Supplemental work orders were issued to inspect and test the supply breakers to F13 and the BAAT room heaters to assure proper operation. The breakers tested properly and no defi-ciencies were f ound.

Installation of ground fault protection on the feeder breakers to individual 480 V AC MCCs will be accomplished per FCR 79-223.

This FCR is presently in the design engineering stage and is scheduled to be completed during the March 1980 refueling outage.

There have been two previously reported occurrences of essential Failure Data:

busses tripoing because of ground f aults; see Licensee Event Reports NP-33-77-48 and NP-33-79-13.

LER #79-088

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