ML19319C124

Deficiency Rept Re GE 480 Volt AK-3A-25 & 505 Breakers: Magnetic Trip Solenoids Failed Trip Test,Power Sensor Time Delays Out of Tolerance & Operational Failures.Supplementing 771003 Interim Deficiency Rept

ML19319C124
Person / Time
Site:	Davis Besse
Issue date:	03/14/1975
From:	Roe L TOLEDO EDISON CO.
To:
References
NUDOCS 8001310484
Download: ML19319C124 (2)

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s TOLEDO EDISON LOWELL E. ROE Docket No. 50-346 [],'[,"g'.*l,l2

.\tarch 14,1975

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Dr. Donald F. Knuth, Director Office of Inspection & Enforcement U.S. Nuclear Regulatory Commission Washington, D. C. 20055

Dear Dr. Knuth:

This letter is submitted in accordance with 10 CFR t' art 50.55 as a consummation on the Interim Report dated October 3,1974 regarding the apparent deficiency related to Davis-Besse Nuclear Power Station No.1 Unit General Electric 480 volt type AK-3A-25 and type AK-3A-50S breakers.

Description of the Deficiency The 480 volt air circuit breakers supplied by the General Electric Company for installation at the Applicant's Davis-Besse Nuclear Power Station Unit No. I were reported to be in apparent nonconformance with expected performance data published by the manufacturer based on on-site testing performed by the Applicant. The basic test equipment and overcurrent tripping curves were furnished by General Electric. The deficiencies noted were:

1. Alagnetic trip solenoids failed to trip when energized by trip signal from test set.

2. Power sensor time delays out of tolerance.

3. Niinor operational failures.

Corrective Action Taken The Applicant directed the General Electric Company to review, analyze and correct all deliciencies with these breakers. Eleven logic units, which were apparently defective, were returned to Q.E. The analyses and corrective actions taken were:

1. h!agnetic trip solenoids failed to trip when using the General Electric test set during on-site testing due to low energy output of test set (discharge of a capacitor) coupled with a slight binding of trip solenoids. A retest at the factory,

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ising fault current for power sourcc, as would be encountered in service, I produced no failures of the trip solenoids. General Electric, to ensure greater rehability, replaced all trip solenoids which had been in question and initiated

" Field Service Advise" (073-SPD-207.8) dated 9/12/74 to their personnel, and additional inspection checks at the factory. The additional inspection checks and gage checks have been effective as no additional problems have been encountered upon the Applicant's re-test of the replacement units. No failures to trip would have occurred if these breakers had been placed in sersice.

. 2. The long time delay concern in 4 of the logic units retu ned was attributable to the accuracy of the power sensor test set used in field test compared to the factory lab equipment. As the result of the Applicant's field tes'; feedback, the factory test has been revised to use higher tripping currents thsn previously used as part of their time delay performance test and the factory set point adjustment band has been narrowed from 23-27 seconds to 23-25 seconds. The apparent widening of band width in the instruction manual (GEK 7301E) for test set use, is only an incorporation of a margin to account for test set accuracy.

No failures to trip would have occurred if these breakers had been placed in service.

3. The minor operational problems in 4 of the power sensor units consisted of a faulty diode, an oversized tap stud, and two poor soldering connections. General Electric replaced the faulty diode and stud and complete sensor units which had soldering problems. Additional control measures have been taken by General Electric in processing control points for logic units and pre-shipment inspection and testing. Three of these breakers could have had failures to trip.

4. Three of the logic units returned were not defective and tripping difficulties 4 (on test set) are attributed to the Magnetic Trip Solenoids covered in number I above.

Safety implications Based on the above, we conclude there are no generic failures of the logie units or trip solenoids supplied by General Electric.

! While the breakers in question were purchased to quality requirements necessary for nuclear safety related t.auipment, none of the questionable breakers were being used in association with engineered safety features equipment. In their balance of plant applications, all 480 volt air circuit breakers have backup protection provided by their associated upstream breakers in case of breaker failure to trip.

The thoroughness and stringency of the Applicant's on-site testing was able to easily establish potential equipment problems prior to placing of equipment in service. Thus, the efety of the plant and public were not jeopardized.

Yours very tr.? ,

J wr e/1-2 cc: J. G. Keppler, Regional Director Office of Inspection & Enforcement Region III

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