ML20086C042

Interim Deficiency Rept Re Automatic Transfer of 4-kV Outside Feed.Initially Reported on 760512.Caused by Design Error.Circuitry for Automatic Bus Transfer Redesigned to Eliminate Possibility of Transfer

ML20086C042
Person / Time
Site:	Salem
Issue date:	06/02/1976
From:	Schwalje E Public Service Enterprise Group
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20086C040	List: ML20086C042
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8311220541
Download: ML20086C042 (4)

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Public Service Electric and Gas Company 80 Park Place Newark, NJ. 07101 Phone 201/022-7000

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June 2, 1976 Mr. Jame s P. O ' Reilly , Director U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region 1 631 Park Avenuc King of Prussia, Pennsylvania 19406 .

Dear Mr. O'Reilly:

AUTOMATIC TRANSFER OF 4KV OUTSIDE FE,ED UO. 1 AUD 2 UNITS -

SA LEM UUCLEAR GENERATING STATION On May 12, 1976 a verbal report was made to Region 1, Office of Inspection and Enforcement advising that an unsatisfactory condition was discovered in the relay logic asacciated with the automatic transfer of vital feeds during the loss of external power. This report was in accordance with the provisions of 10CFR50.55(e).

The following is a detailed analysis and report on the subject:

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DESCRIPTIOU OF DEFICIEUCY The vital bus infeed breaker interlocks were described to the NRC in response to their question 8.6. This response stated, the conditions which must exist in order to transfer a vital bus from its normal source to the alternate source. In the course of reviewing settings for the relays which initi'tiate bus transfer and those which provide undervoltage signals to the Safeguards Emergency Controls System, a condition was dis-covered which could result in a requirement for operator action to assure that vital bus loads would sequence onto the bus.

The design criteria require fully automatic action to initiata bus transfer, to provide " blackout" si6nals to the SEC system, and to proceed with vital bus load sequencing.

AUALYSIS OF SAPETY IMPLICATIONS The condition which was discovered is described below and shown on the attached control schematic.

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.( AN ALYSIS OF SAFETY IMPLICATIONS (Continued)

The design for vital bus transfer incorporates three relays de signated 27-11, 27- 12 and 83- 1. The "27" relays monitor l

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voltage on the secondary side of Mos. 11 and 12 station power transformers respectively, and the 83-1 relay monitors vital bus voltage. If an undervoltage condition were to occur, the 83-1 relay acts to initiate a bus transfer to the transformer which has not lost voltage (as determined by the "27" relays.)

This attempt to transfer is allowed prior to another relay operation which sends a vital bus undervoltage signal to all three SEC units. The relay used for that purpose is designated 27-1 and is properly coordinated with the 83-1 relay to assure that a transfer is attempted before a blackout signal is generated.

During a postulated blackout or LOCA coincident with a blackout, the design is such that the attempted transfer would not occur and the 27-1 relay would initiate a blackout signal in the SEC i units. The SEC, in turn, vould maintain a 5 second trip signal to both bus breakers which supply normal offsite' power to the bus from the station power transformers. Since the diesel-generator breaker would be closed in another 5 seconds,.a 5 second period exists during uhich a bus transfer could occur if en unlikely restoration of outside power to one station power

( transformer were to occur.

l If one of the station power transformers were to be re-energized in this specific 5 second interval,,the bus breaker would close to energize the vital bus. Such a breaker closure would then prevent closure of the die sel-generator breaker and the sequen-cing of safety loads onto the bus. This would occur on all three vital buses and would result in a loss of all bus load sequencing.

The sequencing could be restored if the operator were to. trip any breaker which closed because of~the automatic transfer;cir-cuits or if the 13KV breaker supplying power -to the - transformer were tripped. This action would allow the die sel-gene rator breaker to close and the load sequence to continue.

Even though the conditions which will activate the transfer circuits and subsequent reclosing of.an offsite power source within this 5 second period are considered to be highly unlikely,

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it would require operator action in order to continue with the automatic loading sequence.. This is unacceptable and not in accordance with'our commitment.

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CORRECTIVE ACTION _ ..

The circuitry for automatic bus transfer has been redecignedLb climinate the pocsibility of a transfer any time the 27-l' relhys ,

indicate that diescl-generator loading chould be initiated. . The

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attached control schematics chow that the 27-1 relay will lock-out the automatic transfer capability when. required to do so and A -

provide adequate protection against the unacceptable condition described above.

The hardware and wiring changcc will bc completed by July 15, 19'76.

Should you require additional information our enginesrs will be available to discuss the details with you. ~

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Very truly yours, - .w kE. N. Schwn'je

. dwcd Manager of Quality Assurance-( Engineering'and Construction e-Department Dr. Ernest Volgenau m- _

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