ML20085N308

Ro:On 700915,125-volt Dc Battery Charger Tripped Several Times.Caused by Const Wiring Error That Connected 115-volt Ac to 125-volt Dc at Limit Switch Which Blew Control Circuit Board.Board Replaced

ML20085N308
Person / Time
Site:	Dresden
Issue date:	10/14/1970
From:	Hoyt H COMMONWEALTH EDISON CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8311100355
Download: ML20085N308 (2)

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x{y Morris, Illinois 60450 October 14, 1970 g~L ,... ,^ $I Dr. Peter A. Morris Division of Reactor Licensing

'd.S. Atomic Energy Cotuission SUP, JECT: Licenae i>PR-19 Dresden Nuclear Power Station Unit 2, Section 6.6.C.1 of the Technical Specifications.

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, [', - This is to report a condition relating to the operation of the

,7- station in which the Unit 3 l?5 V DC battery was found to be discharged and the 125V DC battery charger inoperable while the plant was at 600 MWe. The battery and battery charger were required to be operable by Section 3.9B of the technical specifications.

Problem and Initial Action Oa the 12 m - 8:am shift of September 15, 1970, the Unit .3 125V DC battery charg'er tripped several< times. Investigation revealed that the charger was pro-ducing maximum amperage and subsequently tripping on thermal overload. Further investigation revealed what appeared to be a cyclic ground on the Unit 3 125 V DC system.

g Efforts to locate the cause of the trouble were unsuccessful and by 8:00 V

• am September 15, 1970, it was determined that the battery was discharged and that

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the battery charger would no longer proJuce proper voltage. The unit 3 125 V DC battery and battery charge were decipared inoperable at this time. Continued reactor operation was allwed by Section 3.9.3.3 of the Technical Specifications.

The Unit 2 reserve 125 V DC bus was transferred to be supplied from the Unit 2 battery and the 2/3 125 V DC battery charger was placed on the Uni M .

battery to begin recharging it.

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i Investigation and Corrective Action i

I A thorough investigation revuled a Unit 3 construction wiring error that connected 115Vg\

d to the 125 y Du at a ll it switch. This was corrected intnedin tely. 7 i It la believed that the AC signal caused the battery discharge by three rnethods:

a. Blocking the battery chargeroutput.

b. Ticing the battery positive (+) and negative (-) buse: together through the AC syatetas transformer.

l c. Creating a higher than normal driving voltage for normal DC loads.

Trouble ahooting of the batter: :barger revealed a blown control cir-cult board. This was replaced and the Unit 3 125V DC battery charger tested satisfactorily on September 17, 1970. ' ' ~

The Unit ;1 125 V DC battery reached fully charged station on September

_ l 19, 1970. At this time the Unit 3 125 V DC battery and battery charger uas de- l clared operable and the battery system returned to normal lineup.

Th is incident has been reviewed by the Station Review Boardand it was I concluded that the initial action and corrective actions were proper.

i Very truly yours, i

- lllV,0l)% i  :

11. K. Iloy r Superintendent i

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