ML20235P892

Special Rept 89-01:on 890119,smoke Observed Coming from Diesel Generator Regulator Power Transformer Cabinet.Caused by Open Output Fuses from Exciter Power Potential Transformer.Transformer Meggered

ML20235P892
Person / Time
Site:	Callaway
Issue date:	02/21/1989
From:	Blosser J UNION ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
89-01, 89-1, ULNRC-1917, NUDOCS 8903020410
Download: ML20235P892 (4)

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Etscraic 7 February 21, 1989 L <

' Callaway Plant -

U. S. Nuclear Regulatory Cctamission .

'j Document Control Desk '

{! Washington, DC ~ .20555 i

t ULNRC-1917 i

Gentlemen:

DOCKET NUMBER 50 -83 CALLAWAY PLANT tv.T 1 FACILITY OPERATING LICENSE NPF-30 SPECIAL REPORT 89-01 INVALID FAILURE OF DIESEL GENERATOR

'B' DURING TROUBLESHOOTING WHEN 'A' PHASE EXCITER POWER TRANSFORMER HEATED DUE TO BLOWN FUSES l The enclosed Special Report is submitted pursuant to ,

l Technical Specification 4.8.1.1.3 concerning the invalid failure of i Diesel Generator 'B' due to the heating of 'A' phase power potential transformer during troubleshooting. This was due to blown fuses on 'B' and 'C' phases of the transformer.

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. D. Blosser 8903020410999hhjgg Manager, Callaway Plant

{DR ADOCK 05o PDC. 'b oO TPS/MKD:jih Enclosure cc: Distribution attached I

/ if MaHog Aattmsu P.O. Box 62Q Fution, MO 65251 [l j

cc distribution for ULNRC 1917 Mr. A. Bert Davis Mr. Thomas Alexion (2 copies)

Regional Administrator Office of Nuclear Peactor Regulation U.S. Nuclear Regulatory Commission U. S. Nuclear Regulatory Commission Region III Mail Stop 13-E-21 799 Roosevelt Road Washington, D.C. 20555 Glen Ellyn, IL 60137 American Nuclear Insurers Mr. O. Maynard c/o Dottie Sherman, Library Wolf Creek Nuclear Operating Corp.

The Exchange Suite 245 P. O. Box 411 270 Farmington Avenue Burlington, KS 66839 Farmington, CT 06032 Mr. Merlin Williams Manager, Electric Department Supt. of Regulatory Quality &

Missouri Public Service Commission Administrative Services P. O. Box 360 Wolf Creek Nuclear Operating Corp.

Jefferson City, MO 65102 P. O. Box 411 j

Burlington, KS 66839 Institute of Nuclear Power Operations Mr. R. W. DeFayette Suite 1500 Chief, Project Section 3A 1100 Circle 75 Parkway U.S. Nuclear Regulatory Commission Atlanta, GA 30339 Region III 799 Roosevelt Road NRC Resident Inspector Glen Ellyn, IL 60137 D. F. Schnell (400)

G. L. Randolph R. P. Wendling (470)

J. V. Laux A. C. Passwater/D. E. Shafer/D. J. Walker (470)

G. A. Hughes Z170.05 (QA Record)

Z403R (Z170.09 Commercial Record)

M. S. Evans M. E. Taylor H. Wuertenbnecher, Jr. (100)

S. L. Auston (470)(NSRB)

S. J. Bellers/D. R. Oelrichs E210.01 Z40ULNRC A160.761 N. Date (Sandra Auston) (470)

J SPECIAL REPORT 89-01 INVALID FAILURE OF DIESEL GENERATOR 'B' DURING TROUBLESHOOTING-WHEN 'A' PHASE EXC, ITER POWER TRANSFORMER HEATED DUE TO BLOWN' FUSES On 1/19/89, Emergency diesel generator (D/G) 'B' was secured during troubleshooting when smoke was observed coming from the D/G regulator power transformer cabinet. This was an invalid failure which is reported per Technical Specification (T/S) 4.8.1.1.3.

^l A one-hour load rua, required by T/S 4.8.1.1.2.a.5, had been

- successfully completed at 0516 CST. With the D/G still loaded, .

j troubleshooting was undertaken to correct an apparent problem with the '

voltage regulator null meter. A licensed operator attempted to null the meter by raising the manual (base) voltage adjuster while. the automatic (voltage) adjuster was in control. Because the exciter power potential transformer (PPT) 'C' phase fuse had previously, unknowingly blown, the meter would not null and the base adjuster affected the generator output.. The '

effect was seen as an increase in field current and an increase in lagging Kilovolt Amperes Reactive (KVAR's). The generator load reached 6.2 megawatt (MW) at a 0.7 power factor (PF) which corresponds to 8857KVA lagging (this is below the generator 30 minute rating of 9300 KVA). During the' time the operator was troubleshooting the null meter, it is suspected that the exciter PPT 'B' phase fuse failed.

After. discussion between the utility system engineer and the licensed shift supervisor, it was decided to continue troubleshooting with the D/G ,

unloaded. When unloading was halted at 800 KW to stabilize the PF betweer 0.89 and 0.92, smoke was observed coming from the D/G local regulator pot transformer cabinet. The D/G was immediately secured at approximately 0600.

1 Upon investigation, plant personnel discovered the output fuses from the exciter PPT 'C' and 'B' phases were open. The resulting load on PPT 'A' phase, with increased harmonic heating, had caused the PPT to reach l approximately 150*C. This heating caused.a section of clear plastic insulation on the lead to the primary coil of the 'A' phase PPT to melt.

Smoke came from this melted plastic insulation which was installed by the manufacturer to space lead wires.

A visual exmination of the PPT showed a small amount of discoloration on-the top of the 'A' phase primary winding. An engineering evaluation has determined that the 'A' phase coil was not damaged. The 'B' and 'C' phase coils showed no damage.

f' The PPT was meggered. All readings were acceptable. A transformer l turns ratio test indicated no turn to turn insulation damage. The 'C' and

'B' phase PPT fuses were replaced. D/G 'B' was re-started. PPT secondary currents'and temperature were monitored. The manual voltage adjuster was exercised up and down and the null meter responded as expected. A one-hour load test of the D/G was successfully completed. i L

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The 'C' phase PPT fuse is suspected to have blown prior to 1/19/89. An engineering evaluation has affirmed the operability of the D/G with one fuse blown. A review of records shows that the second fuse did not blow until this troubleshooting. The cause of the fuse failures is unknown. A preventive maintenance work request will be evaluated to check the fuses on a routine periodic frequency. The operability of D/G 'A' was also evaluated; its PPT phase fuses were found to be operating normally.

Prior to this event, the D/G had been declared inoperable at 0245 on 1/18/89 to permit preventive maintenance. The D/G 'B' was declared operable at 1831 on 1/20/89. The D/G was unavailable for two days and 15.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />.

T/S 3.8.1.1 action statements were satisfied. Since this failure occurred during troubleshooting and not during a valid test, the surveillance test interval of T/S Table 4.8-1 is not affected. This position is consistent with Regulatory Guide 1.108C.2.e(7).

The starting history of the 'B' D/G as of this report date is summarized as follows:

No. of Failures No. of Failures No. of Valid Tests During Valid Tests During Invalid Tests 69 0 2#

1. Reference Special Report 85-05 Surveillance tests are currently performed at least once per 31 days for the 'B' D/G. This is in conformance with the schedule of T/S Table 4.8-1 which requires a test interval of not more than 31 days if the number of failures in the last 20 valid tests is one or less or the number of failures in the last 100 valid tests is four or less.

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