ML20084E051

AO 50-237/75-20:on 750405,diesel Generator Failed to Field Flash When Started.Caused by Shorted Capacitor.Capacitor Replaced

ML20084E051
Person / Time
Site:	Dresden
Issue date:	04/15/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
255-75, 4274, AO-50-237-75-20, NUDOCS 8304130570
Download: ML20084E051 (2)

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BBS Ltr. #255-75 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 -

April 15, 1975 J

Mr. James G. Keppler, Regional Director '

Directorate of Regulatory Operation-Itegion III U. S. Nuclear Regulatory Comission 799 Roccovelt Road Glen Ellyn, Illinois 60137

SUBJECT:

REPORT OF ABNORMAL OCCURRENCE PER SECTION 6.6.A 0F THE TEEHNICAL SPECIFICATIONS '

UNIT 2 DIESEL GENERATOR FIELD FATTID TO FLASH

References:

1) Regulatory Guide 1.16 Rev. 1 Ap endix A

2) Notification of Region III of U. S. Nuclear Regulatory Commission Telephone: P. Johnson, 1520 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.7836e-4 months <br /> on April 7, 1975 Telegram: J. Koppler, April 7,1975

3) Drawing Numbers 12E-2336 & 12E-2350A

4) Letter from B. B. Stephenson to J. Keppler, Report Number

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50-237/1975-18 n

Report Number: 50-237/1975-20 Report Date: April 15, 1975 -

Occurrence Date April 5, 1975 Facility: Dresden Nuclear Power Station, Morris, Illinois IDENPIFICATION OF OCCURRENCE The unit 2 diesel generator failed to field flash when started after a routine monthly inspection, which represents a condition which could have preyented the performance of the. intended safety function of an engineered safety feature system.

CONDITIONS PRIOR TO OCCURRENCE Unit 2 was in the cold shutdown mode during an extended refueling outage. The unit 2 diesel generator was being returned to service following a monthly inspection.

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cpH SENT REGION,.

April 15, 1975 Mr., ,

James O. -Kepp5r o DESCRIPPION OF OCCURRE'CE

• 0n pril 5, 1975 at approximately 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br />, the Unit 2 diesel generator was *

- started but did not come up to voltage.

DESIGNATION OF APPARMP CAUSE OF OCCURRDICE (Component Failure)

.c The apparent cause for f'ailure has been determined to be a shorted capacitor.

The capacitor paralled the relay that flashes the field. The short lowered the voltage across the relay to a point at which the contacts closed intennittently.

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ANAIXSIS OF OCCURR mCE The health and safety of the public were not in Jeopardy due to this occurrence.

Unit 2 was in a refueling outage and no work was being done that had potential for draining the core. The Unit 2/3 diesel generator was available to act as a backup if necessary.

CORRECTIVE ACTION ,

Following the initial failure, several additional starts were made to locate the source of the problem. The trouble was traced to the Vs relay where abnormal readings were found. The circuit board containing the field flashing circuitry was taken to the shop where further testing indicated the capacitor to be faulty.

The capacitor was replaced and another identical capacitor in the circuit checked innedia tely.

t FAIIIRE DATA A similar incident occurred on the Unit 2 diesel generator on March 19, 1975 (Report Number 50-237/1975-18). The source of trouble, at that time, was thought to be dirty external contacts on the Vs relay. The corrective action (r;ee the above mentioned letter) to add contact inspection to the diesel surveil-lance schedule will be dropped, since the difficulty was found to be in the capacitor.

The diesel generator was purchased from Western Engine Company and manufactured by Electro-Motive Division, General Motors Corporation. It is rated at 2500 kw, 4160 V and 900 RFA. The capacitor is an 8 microfarad, 150. volt electrolytic capacitor manufactured by Aerovox. .

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