ML20028G643

RO-83-01:on 821214,diesel Generator 2B-B Tripped on Differential Overcurrent.On 821216,diesel Generator 2B-B Started But Failed to Exceed 2,000-volt Output.On 821219, Diesel Generator 1B-B Leaked Oil from Tee Fitting

ML20028G643
Person / Time
Site:	Sequoyah
Issue date:	02/09/1983
From:	Green H TENNESSEE VALLEY AUTHORITY
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
R-830209, RO-83-01, RO-83-1, NUDOCS 8302170182
Download: ML20028G643 (3)

Text

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w TENNESSEE VALLEY AU'THORITY CH ATTANOOGA. TENNESSEE 374o1 1750 Chestnut Street Tower II February 9, 1983 Mr. James P. O'Reilly, Director j U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement

'g ' 3 $

Region II T 101 Marietta Street, Suite 3100 .,

Atlanta, Georgia 30303- -

Dear Mr. O'Reilly:

.c-TENNESSEE VALLEY AUTHORITY - SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2*-

SPECIAL REPORT NO. 83-01

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The enclosed special report provides details concerning diesel generator '

problems occurring during surveillance-testing.

Very truly yours, TENNESSEE VALLEY AUTHORITY ih .

j....Greeft Jirector of Nuclear Power Enclosure cc (Enclosure):

Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Records Center Institute of Nuclear Power Operations Suite 1500 1100 circle 75 Parkway Atlanta, Georgia 30339 NRC Inspector, Sequoyah d@CIAL COP.VJ2

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8302170182 830209 7 -# d1 PDR ADOCK 05000327 S PDR An Equal Opportunity Employer m.

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• SEQUOYAH, NUCLEAR PLANT SPECIAL REPORT 83-01 The following events occurred with units 1 and 2 in mode 5.

-1. On December 14,1982, (at 0036C) diesel generator '(D/G) 2B-B was started for its 24-hour run which is' required by surveillance requirement 4.8.1.1.2.d.8. At 1447C on December 14, 1982, D/G 2B-B tripped on differential overcurrent. Following the trip, smoke was spotted coming from the back of the exciter panel. The initial inspection of the exciter high-voltage panel revealed several burned internal control cables, a damaged saturation transformer, and extensive carbon deposits along with other signs indicating phase-to-phase and phase-to-ground arcing. The initial cause of the fault was attributed to control cable insulation degradation which led to the eventual failure. The routing of several of the control cables placed them in direct contact with an opposing phase bus. Once the cable insulation degraded to the point of failure, a phase-to phase fault was created. Corona around the control cable is a suspected cause for the insulation degradation. To prevent future failures of this type, the control cables were rerouted so they would not come in contact with the phase bus. All of the damaged cable along with'the saturation transformer were replaced.

On December 16, 1982, during troubleshooting following installation to the spare saturation transformer, D/G 2B-B was started but failed to exceed 3000 volts output. Investigation revealed a shorted diode in the field rectifier circuit and a broken solder joint on the

" jones plug" to the actuator motor on the 2B1 engine. The solder joint was repaired, the diode was replaced, and the diesel was verified operable. At 1728C on December 16, 1982, D/G 2B-B was again started

~for its 24-hour run and appeared to be operating correctly. At 2228C D/G 2B-B tripped on differential overcurrent due to the failure of the new saturation transformer. The control cabling was not damaged with this failure. Extensive troubleshooting and testing failed to locate any cause for the failure. This failure appeared to have been caused by an internal short in the transformer. With no spare transformers in stock, new transformers had to be fabricated by the manufacturer with a delivery date of December 24, 1982.

On December 22, 1982, the saturation trcasformer from D/G 1B-B was placed on D/G 2B-B and the 24-hour run was initiated on D/G 2B-B. This time the test ran successfully with no problems. On December 24, 1982, the saturation transformer was removed from D/G 2B-B and placed back on D/G 1B-B. D/G 1B-B was then tested to verify operability.

l On December 25, 1982, the new saturation transformers were received from the manufacturer and installed on D/G 2B-B. At 1530C on December 25,1982, D/G 2B-B was started, loaded to 4.4 MW and run for

one hour. The D/G was declared operable at 1636C on December 25, 1982.

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No future corrective action is planned for this event.

2. At 1603C on December 19, 1982, after completing 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> on its 24-hour r"un, D/G 1B-B started leaking oil from a tee fitting on the new lube oil system which was installed during the refueling outage. The D/G was shut down and the oil leak was repaired. The leak was caused by bad threads on a -inch stainless pipe at the tee fitting. After repairs, the D/G was restarted on a new 24-hour run. This was completed with no further problems.

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