ML20118D185

Special Rept:On 920904,invalid Failure of DG 1A Occurred Due to Vibration Trip Sensor Setting Problem.Caused by Inadequacy of Mounting Configuration.Left Front Turbocharger Vibration Switch Adjusted to Less Senstitive Setting

ML20118D185
Person / Time
Site:	Catawba
Issue date:	10/01/1992
From:	Tuckman M DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9210090380
Download: ML20118D185 (3)

Text

. .

ll 1

'^ . imke nmv Company . V$ hinun Carmrba Nw:kar &neratwn ikpartment 17cr hesident A uG Cotswrd Rued (M3)MIJ205 0!ftre brk SC29745 (503)MiJ426 fu

- DUK$ POWER .

October 1,1992 U. S. Nuclear Regulatory Commission

' ATrN: Document Control Desk Washington, DC 20555

Subject:

- Catawba Nuclear Station, Unit 1 Docket No. 50-413 Special Report Invalid Failure of Diesel Generator I A Pursuant to Technical Specification 4.8.1.1.3 and 6.9,2, find attached a Special Report ,

concerning the Unit 1 Diesel Generator A (DG 1A) invalid failure that occurred on September 4,1992.

Very truly yours, be S' W w M. S. Tuckman CRUSRDGI A10.192 Attachment xc: S. D. Ebneter Regional Administrator, Region II W. T. Orders -

Senior Resident Inspector R. E. Martin, ONRR 680.04.2 9210090300 921001 1 i PDR ADDCK 05000413 .

,8

• S PDR v

f

}l

- . ~

v .

-i 4

SPECIAL REPORT CATAWBA NUCLEAR STATION DIESEL GENERATOR 1 A INVALID FAILURES DUE TO VIBRATION TRIP SENSOR SLTI'ING PROBLEM l

l An invalid failure of Diesel Generator (DG) 1 A occurred on September 4,1992 due to a l

left front turbocharger vibration trip. This was caused by difnculties in setting the newly.

installed vibration sensors. This failure occurred during Unit l's_-1EOC6 refueling outage while the unit was in Mode 5. The failure occurred during Operation's Operability Periodic Test (PT) following maintenance on the engine. DG 1 A was on a monthly testing frequency prior to entering the outage. There have been 0 valid failures in the last 20 valid tests and 0 valid failures in the last 100 valid tests. DG 1A remains on a monthly .

operability test schedule in accordance with Technical Specification 4.8.1.1.2 Table 4.8-1.

There is no unavailability time associated with these failures since the Technical Specifications only require one DG during Mode 5. Since DG 1B was operable, DG 1 A was not required.

Modification number CN-lll49 was performed dering IEOC6 outage to replace the non-emergency pneumatic trip instrumentation with electronic trip instrumentation. As part of this modification, the four pneun'atic vibration sensors were replaced with Robert Shaw l'

Model 366 Vibraswitches. Two of these switches are mounted on the engine and t..e other two are mounted on the turbochargers. On August 10, 1992, following the initial installation of ti.cse vibration swi'ches on DG 1 A, problems were encountered during the setting of these switches that resulted in two invalid failures. The problem seen at that time was excessive vibration at the turbocha ger sensors due to the inadequacy of the mounting configuration. An exempt change was initiated to take DG 1 A out of service at a later time in the outage and reconfigure the mounting bracket so that the plate was smaller and not l susceptible to resonant vibration frequencies. DG 1 A was taken out of service on l

September 3,1992 to perform this work. Following the completion of -his work, the DG was run at rull load to set the switches. All the switches were set to trip at 0.5 g's above the normal vibration level The engine was run for several more minutes without any problems and then was shutdown. Operation's then restarted (start 956) the DG for the Openbility Irr and the engine ran fine for approximately 45 minutes. It was at that point, at -1633 hours or. September 4,1992, that the engine tripped on high vibration. No abnormal vibration was seen on the engine at that time. Instrumentation and Electrical Group personnel were called in to investigate the cause of the trip and discovered that the left front turbocharger vibration switch had actuated. The switch was adjusted to a less =

sensitive setting. The proper function of the switch was tested by pinging an area adjacent to the switch an cerifying it tripped as required. The operability PT was repeated without any problems and the engine was declared operable.

No vibration related problems have been seen since then. Ambient vibration levels are j expected to be higher on the turbocharger than on the engine block due to the nature of the turbocharger mounting. Therefore, the turbocharger sensor setting needs to be less sensitive than the engine block sensor setting.

l l

L-

t The vibration trips for the DGs are part of the non-emergency circuitry. On an emergency

- start signal due to a LOCA or Blackout, these trips would be bypassed and the engine would continue to run.

-i Li 2._

i