ML20084M255

Suppl to AO 3-73-2:on 730319,during Test,Component Cooling Water Pump Motor 3A Failed to Automatically Start.Caused by Set of Contacts in Emergency Load Sequencer Relay Welded Together in Closed Position.New Closing Coil Installed

ML20084M255
Person / Time
Site:	Turkey Point
Issue date:	08/31/1973
From:	Schmidt W FLORIDA POWER & LIGHT CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084M254	List: ML20084M251 ML20084M255 ML20084M263 ML20084M275
References
AO-3-73-2, NUDOCS 8306020068
Download: ML20084M255 (4)

Text

P o. BOX 3100 M1AMI, FLORIDA 33101

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.m TJl l FLORIDA POWER & UGHT COMPANY-August 31,'1973 .

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Mr. John F. O' Leary, Director 6 ,/ ,

Directorate of Licensing _

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TURKEY POINT UNIT NO. 3 Em 6;( Y DOCKET NUMBER 50-250 /

SUPPLE!ENT TO ABNOR'.tAL OCCURRENCE NO. 3-73-2 cn FAILURE OF NO. 3A COMPONENT COOLING WATER PUMP WIOR TO AUlG!ATICALLY START

Dear Mr. O' Leary:

I. INTRODUCTION On March 19, 1973, Abnormal Occurrence Report No. 3-73-2, which concerned the failure of No. 3A Component Cooling Water Pump Motor to automatically start, was submitted in accordance with Technical Specification 6.6.2.a for Turkey Point Unit No. 3, Operating License No. DPR-31. s This supplemental report presents the results and evaluation of test's performed to provide assurance that the cause of the failure of No.

3A Component Cooling Water Pump to. automatically start was determined and corrected.

II. PROBLB1 AND INVESTIGATIVE ACTICN ,,

BACKGROUND:

During the performance of a functional test which intentionally de- -

energized both No. 3A and 3B, 4160 volt buses, No. 3A Component Cooling Water Pump Motor failed to automatically start. Investigation by plant personnel revealed that a set of contacts in the emergency load sequencer relay were " welded" together in the closed position.

An interlock feature associated with No. 3A Component Cooling Water Pump Motor circuit breaker closing circuit, prevented this circuit breaker from closing as long as these relay contacts were " welded" together in the closed position. This resulted in the failure of No.

3A Component Cooling Water Pump Motor to automatically start during the functional test involving the loss of voltage to both Nos. 3A and 3B, 4160 volt buses. -

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Mr.JohnF.O'15ary August 31, 1973 TEST MElliOD AND RESULTS:

1. The circuit involving the " welded" relay contacts was changed to use a spare set of contacts in the same emergency load sequencer relay. No. 3A Component Cooling Water Pump bbtor circuit breaker was then tested and perfonned satisfactorily.

This test demonstrated that the cause of the failure of No. 3A Compor.cnt Cooling Water Pump Motor to automatically start was caused by the " welded" contacts in the emergency load sequencer relay. _

2. A Spare circuit breaker of the same type as No. 3A Component Cooling Water Pump hbtor circuit breaker was placed in the installed 4160 volt circuit breaker test stand. A test circuit was established to operate the breaker in the test stand using a spare set of contacts in the emergency load sequencer relay.

The Spare breaker was closed and opened about 100 times while using the test circuit and observing the performance of the relay contacts. Visual inspection of the relay contacts at the con-clusion of the test showed no signs of arcing, overheating, or other abnormalities.

3. No. 3A Component Cooling Water Pump bbtor breaker was then tested under the identical test conditions described above. After about five cycles of circuit breaker operation, the relay contacts were observed to be arcing or flashing over. While continuing to test this breaker, the tips of the relay contacts showed signs of signi-ficant overheating. This test was concluded when the relay contacts

" welded" closed and the circuit breaker would not operate. This same test was rerun using another spare set of relay contacts and identical results were obtained. This second set of relay contacts

" welded" closed and the breaker would not operate.

A review and evaluation of both of the above tests concluded that components within the No. 3A Component Cooling Water Pump Motor circuit breaker were causing the emergency load sequencer relay contacts to be " welded" closed.

4. An investigation was made of the components installed in the closing circuit of No. 3A Component Cooling Water Ptunp Motor circuit breaker i

during the test which caused the " welding" of emergency load sequencer relay 34Y/3A3b contacts. This inspection revealed no indications of problems with the limit switches, connections, or indications of over-heating. Accordingly, the installed circuit breaker closing coil was renoved and replaced with a new closing coil. No. 3A Component Cooling Water Pump circuit breaker was tested under the idential test conditions described above. Visual observation of the relay during about 100

ycles of operation showed no signs of arcing, overheating or other abnormalities. Review and evaluation of the results of this test ton-cluded that the closing coil was the component which caused the emergency

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' Mr. Johil F. O Leary August 31, 1973 load sequencer relay contacts to be " welded" together in the closed position. .

5. The closing coil, which was removed from No. 3A Component Cool-ing Water Pump bbtor circuit breaker, was meggered and the insulation was found to be satisfactory. The resistance of this closing coil was then measured and compared with the resis-tance of a new closing coil. This comparison showed that the resistance of this closing coil was within expected tolerances. ^

This closing coil was then disassembled for a visual inspection for any abnormal conditions. The varnish insulation was found to be satisfactory and no abnormalities were found.

Although a review of results of inspections of the closing coil indicated no significant differences between measured values of electrical characteristics of the closing coil and those of a new closing coil, evaluation of the results of performance tests with the closing coil and a new closing coil concluded that the closing coil was breaking down under load and became defective during operation of the circuit breaker. This was demonstrated during repeated operation of the circuit breaker which resulted

'in excessive current flow in the closing coil circuit and the emergency load sequencer relay contacts were welded together.

s III. DISCUSSION A review and analysis of the results of these tests, inspections, and checks perfomed on the emergency load sequencer relay and the circuit

-breakers concluded that the failure of No. 3A Component Cooling Water Pump bbtor to automatically start was caused by the emergency load sequencer relay contacts being welded together in the closed position.

Additional tests showed that the components installed within the No. 3A Component Cooling Water Pump hbtor circuit breaker closing circuit caused arcing, overheating and welding of the relay contacts. Removal and re-placement of the installed closing coil with a new closing coil in the No. 3A Component Cooling Water Pump bbtor circuit breaker eliminated the problem of arcing, overheating and welding of the emergency load sequencer relay contacts.

IV. CORRECTIVE ACTION TO PREVENT RECURRENCE Installation of a new closing coil in the No. 3A Component Cooling Water Pump bbtor circuit breaker has corrected the problen of arcing, overheating and welding relay contacts associated with emergency load sequencer relay 34Y/3A3b. This was demonstrated by operating this breaker through about 100 cycles with no visual indications of arcing.,

overheating or damage to relay contacts.

%J Mr. John F. O' Leary August 31, 1973 V. CONLLUSIONS

a. A review and evaluation of test results presented above concluded that the failure of No. 3A Component Cooling Water Pump bbtor.to automatically start was caused by emergency load sequencer relay contacts being welded together in the closed position.

b. Tests demonstrated that the components installed within the No.

3A Component Cooling Water Pump bbtor circuit breaker caused arcing, overheating and welding of the relay contacts in the emergency load sequencer relay, and were unique to No. 3A Component Cooling Water

• Pump bbtor circuit breaker.

c. Although a review and evaluation of the results of inspections and electrical tests of the closing coil installed in the 3A Component Cooling Water Pump motor circuit breaker did not indicate any signi-ficant defects in the closing coil, it was conciuded that the closing coil was breaking down under load and caused excessive current flow in the closing coil circuits during operation of the circuit breaker.

d. Review of operation and maintenance records for Unit Nos. 3 and 4 revealed that a similar incident involving No. 3A Component Cooling Water Pump motor breaker occurred on August 17, 1972. In view of the analysis and evaluation presented above, it may now be concluded that this failure of No. 3A Component Cooling Water Pump motor breaker ,

to close was caused by emergency load sequencer relay contacts being welded together as a result of excessive current flow in the closing coil circuits during operation of the circuit breaker.

e. Installation of a new closing coil in No. 3A Component Cooling Water Pump motor circuit breaker closing circuit corrected the problem of arcing, overheating and welding of emergency load sequencer relay contacts. This corrective action should prevent the recurrence of this and similar incidents. .

Very truly yours,

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e. D. Schmidt Director of Power Resources ADS /JKH/DNJ/VTC/m1w cc: Mr. Nonnan C. hbseley, Director Region II, Directorate of Regulatory Operations U.S. Atomic Energy Commis A n Suite 818, 230 Peachtree Street, N.W.

Atlanta, Georgia 30303 O

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