ML19210A195

Abnormal Occurrence 50-289/75-25:on 750721,failure of Diesel Generator a Frequency Relay to Actuate,Threatening Nonperformance of Diesel Generator.Cause Presently Unknown

ML19210A195
Person / Time
Site:	Three Mile Island
Issue date:	07/31/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
Shared Package
ML19210A196	List: ML19210A195 ML19210A199
References
GQL-1333, NUDOCS 7910240916
Download: ML19210A195 (4)

Text

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NF -.STRIBUTION FOR PART 50 dor . MATERI AL (TEMPOR ARY FORM) s CONTROL NO: 27 FILE: INCIDE:7T REPCRT FI'.L

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FROM: Reading, Penna. DATE OF DOC DATE REC'D LTR TWX RPT OTHER

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CLASS UNCLASS PROPINFO INPUT NO CYS REC'D DOCKET NO:

CC: 1 53-250 DESCRIPTION:

• ENCLOSURES:

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Dear Sir:

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• tj- ^>4 Docket No. 50-239 6 Operating License No. DPR-50 In accordance with the Technical Specificaticns of our Three Mile Island Nuclear Station Unit 1 (TMI-1), we are reporting the following abnormal occurrence.

(1) Repcrt Number: A0 50-289/75-25 (2a) Repcrt Date: July 31, 1975 (2b) Occurrence Date: July 21, 1975 (3) Facility: Three Mile Island Nuclear Statien Unit 1 (h) Identification of Occurrence:

Title:

Failure cf a frequency relay for the "A" Diesel Generator to actuate.

Type: An abnormal occurrence as defined by the Technical Specificatiens, paragraph 1.8d, in that failure of the "A" Diesel Generater frequency relay to actuate ecnstituted a failure of cne cc=ponent of an engireered safety feature that threatened to cause the Diesel Generater to be incapable of performing its intended functions.

(5) Co:.ditions Prior to occurrence:

Pcver: Core: 99 ".

Elect. 832 'Ge (gros s )

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- .- <. :. s RC Flev: 137 x 10 lb/hr RC Press: 2160 psig T A76 204 . . ,

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RC Te=p.. 579 F PRZR Level: 220 inches PRZR Terp.: 6550F (6) Descripticn of Occurrence:

On July 21 the A diesel generater vss started and Icaded for rcutine testing. It was noted by visual inspecticn that cne of the three frequency relays (81-3) was not picked up. The other tvc frequency relays associated with the A diesel generator were pi:ked up. It is believed that the generator was cperating at 60 cycles /seccnd at the ti=e the relays were observed. The relays are set to pick up Et >>

cycles /seccnd.

The three frequency relays serve as an interleck that allows the breaker to close when the diesel generator is up to speed. The relays are ccnnected in a two out of three logic so that failure of one relay does nct prevent the breaker frem closing.

The suspect relay was re=oved frem service and the setting was checked en the bench. A replace =ent relay vss tested and installed in the cabinet. The diesel generator was started and all three frequency relays were verified as having picked up when the generator was up to speed.

A bench test of the suspect relay revealed that the relay operated at 59 2 cycles per second. The internal connecticns were checked. One ecnnection was tightened slightly; hcVever, tightening the connection did not change the pick up value significantly and the connecticn was considered satisfactory.

The relay was set to 59.0 cycles per second and put back in the sa=e position en the A diesel generator. The diesel was cperated and it was verified that the relay picked up when the diesel was up to speed.

(T) Designation of Apparent Cause of Occurrence:

The apparent cause cf this cccurrence is not kncvn but possible causes are:

a. It has not been definitely established that the Diesel was operating at 60 cycles /sec. at the time that the frequency Relay was ob s e rved.

b. Setting drift =ay have contributed to the failure in that the setting had drifted frc= 59 cycles per second to 59.2 cycles per second. This should not have kept the relay fren being picked up at 60.0 cycles per seccnd.

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c. Dust er dirt may have caused the f ailure by becc=ing lodged in the bearings for the induction disk. The dirt, if present, may have become dislodged when the relay ves re=oved frc= the cabinet for testing.

(8) Analysis of Occurrence:

It has been determined that failure of the 81-3

• alt / did net represent a threat to the health and safety of the public, in that:

a. The 1A diesel generator was cperable as 2 cf the 3 frequency relays operated properly alleving the breaker to close.

b. The 3 diesel generator was operable and one diesel generater is sufficient to supply necessary safety related equipment in the event of loss off site pcVer.

(9) Corrective Actions:

In addition to the i=nediate corrective actions listed above icng tern corrective actions are as follows:

The relay cabinets for both diesel generators vill be cleaned to reduce the possibility of dirt getting into the relays. The remaining 2 frequency relays for the A diesel generater vill be cleaned and checked to assure that they are calibrated and operating prcperly. In addition, the voltage of the signal to the frequency relay will be checked to assure that adequate voltage is present to cperate the relays.

The existing surveillance procedures for maintenance and calibratien of the relays vill be reviewed to assure that the precedures are adequate.

The Plant Operations Review Cc==ittee and Statien Superintendent have reviewed and approved the above corrective actions and have taken steps to ensure cc=pletion of the yet to be ec=pleted long tern corrective actions.

(10) Failure Data:

Westinghouse CF-1 Frequency Relay Style 291 E995410 Similar Occurrences: Ncne Sincerely, e ,e j4]{ ))6 9

h ># U R. C. A9nold Vice President RCA :CZS :tas ec: Office of Inspection and Inforcement, Region 1