ML19326B313

AO 50-313/74-01:on 740526,emergency Diesel Generator K4B Synchronized Through Breaker 152-408 & Tripped by Actuation of anti-motoring Relay.Caused by Incorrect tolerances.Anti- Motoring Relay Holding Coil Setting on K4B Adjusted

ML19326B313
Person / Time
Site:	Arkansas Nuclear
Issue date:	06/05/1974
From:	Cavanaugh W ARKANSAS POWER & LIGHT CO.
To:
Shared Package
ML19326B312	List: ML19326B311 ML19326B313 ML19326B314
References
NUDOCS 8004150700
Download: ML19326B313 (2)

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O's e Abnormal Occurrence Report No. 50-313/74-1 Report Date: June 5, 1974 Occurrence Date: May 26, 1974 Facility: Arlansas Nuclear One-Unit 1 Identification of Occurrence:

Emergency Diesel Generator Failure Conditions Prior to Occurrence:

Plant shutdown; preparation for initial fuel loading in progress.

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Description of Occurrence:

During routine surveillance testing at 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br /> on May 26, 1974, emergency diesel generator K4B was synchronized through breaker 152-408 and tripped by actuation of the anti-motoring relay. The lockout relay was reset and the diesel restarted at which time it trippe'd by actuation of the overspeed relay.

Emergency diesel generator K4A had been successfully tested prior to this occurrence.

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Designation of Apparent Cause of Occurrence:

Incorrect tolerances.

Analysis of Occurrence:

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An investigation undertaken on K4B revealed that the governor was not s responding properly, thus causing the unit to overspeed. Emergency diesel generator K4A governor was tested at this time and responded properly. 4 i

4 During this investigation it was determined that the anti-metoring relay was not operating properly. The anti-motoring relay holding coil setting was close enough to produce a false trip from contact bounce by sealing

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in on voltage alone.

'Ihe emergency diesel generators were not required to be operable for the plant conditions at the time of this occurrence. Thus, no limiting condi- '

tions for operation or' safety limits were exceeded. The discovery of this condition during routine surveillance activities indicates the effectiveness

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of surveillance activities .n ensuring reliability of plant systems and equipment.

At no time during this occurrence was the integrity of the redundant diesel generator K4A compromised. Consequently, even if this event had occurred p during power operation, sufficient capability would have been available to

{ j bring the plant to a safe shutdown condition in a timely manner without V hazard to public health and safety.

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( Abnormal Occurrence Report No. 50-313/74-1 Page 2

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Corrective Action:

! Re anti-motoring relay holding coil setting on K48 was adjusted per General Electric manual gel-33891 (Section on Maintenance and Calibration),

such that it will trip on current and voltage, thus giving a valid trip.

f. The unit was loaded and the synchronizing breaker (152-408) opened to j verify that the anti-motoring relay did not falsely actuate and thereby trip the lockout relay. His test was conducted three times with proper

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response.

The anti-motoring relay on K4A was also adjusted and K4A was tested to assure the prevention of a similar occurrence.

The K4B governor (flodel ifoodward UG8) sensitivity was adjusted per vendor -

recom.nendations. After adjustments were completed, K4B was fully loaded, tripped and restarted three times with proper unit response. No adjust-ments were made during the test.

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He overspeed trip setting on K4A and K4B will be increased from 980 rpm to between 990 and 1C05 rpm per vendor recommendation found in instruction book " Electro-Motive 645E4 Engine llanual".

Failure Data:

r One previous failure has occurred on emergency diesel gneerr. tor K4A as -

reported on September 10, 1973. That incident involved the failure of an isolation potential transfomer located in the diesel generator excitation control cubicle which caused the voltage regulator to malfunction, thus tripping the Engineered Safegucrd Bus feeder breaker.

The .5N0-1 emergency diesel generators utilize General Motors Electro- 3 Motive Model No. '0-645E4 Engines.

Reviewed by: $4 '/ , Z / <s .. -[ // Date: / 'l - ['/

afety Revie 'ttee /,

Reviewed by:

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Manager, Nuclear Servicep

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Reviewed by: @< 4 </< , [ Date: 6 - / 7/

/ Director, Power P,roduction -

Approved by: h/ <

< , Senior Vice President Date: [~'I-2 -

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