ML20059E736

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Special Rept:On 931203,three Invalid Failures of Diesel Generator 1B Occurred Due to High Vibration Engine Trip. Corrective Maint Performed on Generator Splash Guard Louvers
ML20059E736
Person / Time
Site: Catawba Duke Energy icon.png
Issue date: 01/04/1994
From: Rehn D
DUKE POWER CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9401120209
Download: ML20059E736 (3)


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January 4, 1994 l

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Nuclear Regulatory Commission ATTN:

Document Control Desk Washington, DC 20555 i

Subject:

Catawba Nuclear Station, Unit 1 Docket No. 50-413 Special Report Invalid Failures of Diesel Generator 1B 3

Pursuant to Technical Specification 4.8.1.1.3 and 6.9.2, find attached a Special Report concerning the Unit 1 Diesel Generat.or (DG 1B) invalid failures which occurred on December 3, 1993.

l Very truly 3ours,

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g DL Rehn KEN \\DGlB1203.93 i

Attachment xc:

SD Ebneter Regional Administrator, Region II RJ Freudenberger Senior Resident Inspector RE Martin, ONRR c

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4 SPECIAL REPORT CATAWBA NUCLEAR STATION DOCKET NO. 50-413 DIESEL CENERATOR IB INVALID FAILURES DUE TO HIGH VIBRATION ENGINE TRIPS i

PIP 1-C93-1054 l

Three invalid failures of Diesel Generator 1B (DG 1B) occurred on December l

3, 1993 due to high vibration engine trip.

This is a non-emergency trip which is bypaused on an emergency start; therefore, the failure is classified as an invalid failure. Unit 1 was in Mode 6 (refueling) for the 1EOC7 ref ueling outage at the time these f ailures occurred. There have been O valid f ailures in the last 20 valid tests 'and 0 valid failures in the last l

100 valid tests.

DG 1B remains on a monthly operability test schedule in accordance with Technical Specification (TS) 4.8.1.1.2 Table 4.8-1.

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1s 32.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> unavailability time associated with these failures.

On December 3, 1993, DG 1B was manually started at 1322 (Start #1034) and fully loaded using PT/1/A/4350/028 (Diesel Generator IB Operability Test) following corrective maintenance which had been performed on the generator splash guard louvers.

Approximately 30 minutes into the run, the engine l

tripped on high vibration on the left bank turbocharger. This failure was t

classified as an invalid failure.

Prior to the engine trip, the generator load was observed to varying from 5750KW to 5400KW.

I Instrument and Electrical (IAE) de-activated the high vibration trip'and readjusted the setpoint to allow slightly greater vibration per work order 93087560-01. DG 1B was manually restarted at 1740 (Start #1035) and loaded, per OP/1/A/6350/02 (Diesel Generator Operation) following this adjustment.

l After an approximate 20 minute run, IAE re-activated the high vibration

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trip.

Approximately 30 minutes into the run, the load swing pattern began-again and the engine tripped on high vibration. This f ailure was classified j

as an invalid failure.

f IAE again de-activated the high vibration trip signal.

DG 1D was started again at 1928 (Start #1036) and loaded per OP/1/A/6350/02.

The load swing pattern was again observed about 30 minutes into the run.

The engine was then manually shutdown. This failure was classified as an invalid failure.

l The high vibration trip signals were de-activated for the entirety of this third run.

'l Component Engineering (CES) and Mechanical Maintenance (M/M) personnel e

examined the blower end of the turbocharger by removing the expansion joint i

under work order 93087560-02.

It was observed that the blower end of the shaft was able to be wobbled by hand.

Based on this observation, the CES engineer decided the turbocharger was experiencing excessive bearing wear and should be replaced. The suspect turbocharger was removed from the DG 1B engine, and a rebuilt turbocharger was installed on the engine.

On December 5,

1993, DG 1B was manually started at 0659 (Start #1037) and

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run loaded for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> per OP/A/1/6350/02 with no vibration trips.

During this 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> run, the M/M crew monitored the engine and observed load swings.

In each case, the load would drif t slowly down to 5300-5400KW, then slowing climb back to 5750KW, then drift back down.

This behavior continued from t=30 min to t=60 min.

During the second hour of this run, the behavior was not evident. During this run and also during the runs on December 3,

1993, all other Cylinder parameters Were acceptable and no unusual engine conditions other than the vibration trip were noted, j

i Root cause analysis on the turbocharger is still in progress.

A representative ~ f rom the turbocharger manuf acturer, Elliott Company, observed the disassembly of the suspect turbocharger at Catawba on December 8, 1993.

The turbocharger's journal bearing clearances were satisfactory as was the axial thrust bearings.

There~were no signs of unusual or abnormal wear.

- The rotor assembly in its entirety has been sent to Elliott Company.for an evaluation of. its balance condition. Representatives of Duke Power Company will observe this testing.

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l-SPECIAL REPORT I

CATAWilA NUCLEAR STATION DOCKET NO. 50-413 4

DIESEL GENERATOR IB INVALID FAILURES f

DUE TO IIIGli VIBRATION ENGINE TRIPS PIP l-C93-1054

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The preliminary conclusion drawn by CES is that the load swings suf ficiently shook the engine to cause the high vibration trip. Whether there was a pre-6 I

existing condition in the turbocharger which exacerbated this problem may be det. ermined by the manuf acturer's evaluation.

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Programmatic changes in the short-term will be to increase the vibration monitoring frequency to monthly on DG 1B; and to investigate the wobble issue by inspecting the blower end of the turbochargers at the completion of -

their monthly run.

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on December 5,

1993, DG 1B was started at 1124 (Start #1038) per

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PT/1/A/4350/028. This start attempt was declared a valid success and DG 1B was declared operable at 1430.

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