ML19347C940

Interim Deficiency Rept Re Defective 480V Switchgear Trip Units,Initially Reported on 801126.Problem W/Power Shields Has Been Corrected.Investigation of IAW 504 & multi-amp Tests Is in Progress.Final Rept Will Be Provided by 810330

ML19347C940
Person / Time
Site:	Summer
Issue date:	03/06/1981
From:	Nichols T SOUTH CAROLINA ELECTRIC & GAS CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8103100362
Download: ML19347C940 (4)

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March 6, 1981 j{

h<! $f 3*M y a, lA g:.0 +Cd Mr. James P. O'Reilly, Director e,$.

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U. S. Nuclear Regulatory Commission

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Region II, Suite 3100 101 Marietta Street, N. W. .! E Atlanta, Georgia 30303 9n' act: Virgil C. Sum =er Nuclear Station Docket No. 50/395 Potential Substantial Safety Hazard Interim Report Nuclear Eng. File 3.1051

Dear Mr. O'Reilly:

On November 26, 1980, Mr. Bob McFarland of NRC Region II was notified of a potential substantial safety hazard on the subject: Defective 480 Volt Switch-gear Trip' Units. The report was made by Mr. J. A. Wactor.

Two' interim reports on this subject was made by letter to you dated December-23, 1980, and January 30, 1981. Enclosed is a report that gives an update on .the work that has been done, but we still have some unresolved concerns.

We expect to have a resolution and a final report by Macch 30, 1981.

Very truly yours

", o G T. C. Nichols, Jr.

.TB:TCN:glb Enclosure ec: V.' C. Summer J. B. Knotts, Jr.

'G. H. Fischer J. L. Skolds

'T. C. Nichols,-Jr. B. A. Bursey

.0.'W.-Dixon, Jr. 0. S. Bradham

• C..A. Price ~ -Document Management Branch D. A. Nauman. (55e/21/LER Only)

W. : A. . Williams ,-:Jr. I&E (Washington)

R..B. Clary. ISEG A. R. Koon-A.~A. Smith PRS

.NPCF/Whitaker f

~H. N..Cyrus. File j l.l.

J3108100 3

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O Review of Defective 480 Volt Switchgear Trip Unit

. Two power shields (#32385 and #34049) in~ associated ITE, breakers'where found i to f ail' while in service. A power shield is a three phase solid state, over current trip device designed for low-voltage power system protection against damage caused by over load and short circuit conditions.

I Power shield #32385 was in breaker XEN-233 associated with fuel handing

. exhaust fan on 480 volt safety related bus. The power shield #32385 passed tests on the IAW 504 equipment tester and the primary current multi-amp tester but when incorporate in the switchgear which feeds the fuel handing exhaust fan, the breaker would trip when the fan was started. The breaker was given a new power

' shield series #44242 and the breaker operated properly.

Electrical maintenance and Nuclear Engineering determined that the power shield #32385 was defective, but are not.sure why it passed the earlier IAW 504

' tests' equipment test and the multi-amp test?

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b Power shield #34049 was associated with.non essential 480 bus LAS feeding 4

Lsecurity building air condition.

t

!' The IAW 504 test equipment tests the power shield for proper operation. It

~

,does.not test the' actual breaker. The multi-amp tester is used to tests the

' breaker with its associated power-shield. -The breaker is taken out of the switchgear and brought: to the lab for testing. The multi-amp tester supplies ihe currents to the breaker to determine if the breaker will trip at the proper set posits. .Although.the multi-amp. tests are at the correct currents, the The breaker in service fvoltage of: the multi-amp : tests are only 3 or 6 volts..

l actually sees 480 . volts. Thus the breaker sees higher voltages than that

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fdelivered by the' multi-amp tester.

L 5

O Factory Repairs and Findings ITE (Could) sales representative, Mr. Bob Watson, visited V. C. Summer Plant on November 12, 1980. V. C. Summer Plant Technical Support Engineering, QA and Electrical Maintenance personnel met with Mr. Watson and explained :he problem addressed in NCN #055. Mr. w'atson said that they had not encountered this problem before (Power Shield checking good IAW 504 tests equipment and Multi-Amp test equipment, but tripping when put on line with a load that was not drawing trip magnitude current). Mr. Watson was given a copy of EMP-405.2 to send to ITE design engineers for re-evaluation to insure that our procedures for testing these circuit breakers are adequate. He also will have them in-vestigate this situation to determine what could cause this problem and what action can be taken to preclude a re-occurrence.

There has been no re-occurrence of this problem, and since it happened some time ago, it appears that this problem was isolated to these two power shields (serici nos. 32385 and 34049). Said power shields uere returned to the factory.

ITE reported that when the power shields were examined at ITE factory, one power shield unit has a loose connection. The unit'appearr.J to have been drop-

. ped or received a severe impact. Physical misuse was apparent. The other unit appeared to be in good condition. Light corrosion was found on one contacc.

There were no other damages to the unit. The units were repaired, tested and returned to V. C. Summer Plant.

V. C. Summer Electrical Maintenance Tests After the two power shields were returned back to V. C. Summer Plant, elec-trical maintenance performed their own tests on the two units.

Power shield #32385 was. tested on the IAW 504 tester and passed the test.

This power shield was taken to the warehouse for a spare power shield.

O Power shield #34049 was tested with both the IAW 504 tester on the power shield and then the multi-amp test on the breaker. Both test were successful.

The' breaker with its associated power shield was closed on the 75 horsepower machine shop lathe with no problems. These test support the ITE's findings that the ur.it has been repaired.

Investigation Result ITE design engineer evaluated the V. C. Su=mer test procedure, EMP-405.2 and determined that the procedure for testing these power shields and circuit

-breakers are adequate.

Nuclear Engineering realized that since the multi-amp tester only uses 3 or 6 volts and not 480 volts, the tests do not simulate the in-service conditions lof the breaker. For example, a problem could exist where the 4SO volts with its associated current would cause electric field breakdown within the breaker.

However, the lower 6 volts and its associated current would not cause electric field breakdown because it-does not supply the higher voltage.

ITE" factory has found and corrected the problem with the power shields and there has been no re-occurrence of this problem, and since no other similar

' problem has occurred, it appears that the problem was isolated to these two power shields.

Nuclear Engineering does not have~an exact answer why the power shields and breaker pissed both tests but ! failed when the breaker was put into service.

1 SCE&G Nuclear Engineering will continue the investigatioa to take a closer look at,both the IAN 304 test'and the multi-amp test to determine if any possible problem e'xist,

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