RBG-31520, Special Rept:On 890823,diesel Generator Tripped Due to High Vibration Signal from Turbocharger Vibration Trip Switch. Possibly Caused by Leakage of Air Around O-rings in Shuttle Valve of Trip Switch.Switch Taken Out of Svc

Special Rept:On 890823,diesel Generator Tripped Due to High Vibration Signal from Turbocharger Vibration Trip Switch. Possibly Caused by Leakage of Air Around O-rings in Shuttle Valve of Trip Switch.Switch Taken Out of Svc

ML20247P028
Person / Time
Site:	River Bend
Issue date:	09/15/1989
From:	Booker J GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-31520, NUDOCS 8909260372
Download: ML20247P028 (6)

Text

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m e cr ea e x. s.:~ .oc ers, September 15, 1989 RBG- 31520 File Nos. G9.5, G9.25.1.4 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Gentlemen:

River Bend Station - Unit 1 Docket No. 50-458 Enclosed is Gulf States Utilities Company's Special Report concerning an invalid failure of the Division I diesel generator at River Bend Station. This report is being submitted pursuant to River Bend Station Technical Specification 4.8.1.1.3 and 6.9.2.

Sincerely, 9.F.&s, J. E. Booker Manager-River Bend Oversight River Bend Nuclear Group f0 Y

JEB/TFP/RGW/ M/KRK/ch cc: U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Resident Inspector Post Office Box 1051 St. Francisville, LA 70775 h

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i l SPECIAL REPORT At 2148 on 8/23/89 while performing surveillance testing on the Division I diesel generator (DG), an invalid failure occurred due to a trip from high turbocharger vibration. In accordance with Regulatory Guide 1.108 the following information is provided:

l Diesel Generator Unit Designation and Number: Division I, IEGS*EGIA Cause of Failure:

At 2148 on 8/23/89, while performing Surveillance Test Procedure (STP)-309-0201, " Diesel Generator Division I Operability Test" to demonstrate the operability of the Division I DG, the DG tripped due to a high vibration signal from the turbocharger vibration trip switch. The DG had been started at 2117, the output breaker was closed at 2122 and the DG was then loaded to 3100 KW (100% load). This trip is categorized as an invalid failure in accordance with Regulatory Guide 1.108 Position C.2.e.(2) since vibration readings taken during the next diesel run, which commenced at 0147 on 8/24/89, were not higher than baseline readings taken during the first two operating cycles (fuel cycles). Also, since vibration trips are automatically bypassed in the emergency operating mode of the DG, the actuation of this trip device would not have shut down the unit or rendered it inoperable had it been operating in response to an actual emergency.

The vibration switch which initiated the trip had been installed immediately before the operability run, and had been calibrated during a short duration engine run especially for that purpose. This short run was necessa ry since the switch is set to trip at a prescribed setting above a background level of normal diesel operation at 100% load. The new switch installation was a follow-up action to a previous vibration trip where the switch was found to be defective following retest, (reference letter RBG-31090 dated 6/15/89).

Past station maintenance records for the diesels were reviewed. Numerous instances were found where new switches were defective or became defective after a short operating life. Other utilities which use Enterprise diesel engines with Calcon E4600A vibration switches were consulted and it was reported by those who bench tested the new switches before installation that 50% or more failed. Design Engineering's preliminary conclusion is that the vibration trip was spurious in nature, caused by a defective trip switch.

The mode of failure may be due to leakage of air around the 0-rings in the shuttle valve of the trip switch.

The vibration trip switch was taken out of service, and procedure STP-309-0201 was successfully reperformed. The vibration switch mounted on the engine block remained operative, and will continue to provide protection for the diesel engine. Design Engineering evaluated return of the DG to operable status with the turbocharger vibration switch bypassed, and determined this condition to be acceptable because the vibration switch is automatically bypassed in the emergency operating mode.

Page 1 of 2

l ..

. . 1 With the turbocharger vibration trip manually bypassed, the following parameters will be monitored when the diesel is run:

1. Turbocharger oil pressure

2. Combustion air pressure

3. Turbocharger vibration levels and support integrity

4. Turbocharger noise level for any unusual sounds If any unusual conditions are noted on any of these four parameters, the operators i' ave been instructed to shut down the DG if it is not operating in the emergency mode.

Corrective Action:

Replacement of the vibration switch is scheduled for the next diesel generator outage. Replacement will include bench testing of the switch to determine its functional reliability prior to installation. Design Engineering has provided Maintenance with a test procedure which exactly duplicates the operation of the vibration switch during engine start, vibration lockout, safety shutdown system activation, vibration trip, and reset.

Current Surveillance Intervals: Division I: Monthly Division II: Monthly Division III: Weekly Test Intervals Conform to Technical Specifications: Yes Failures for Division I: 0 valid failures in previous 20 valid tests 0 valid failures in previous 100 valid tests Failures for Division II: 0 valid failures in previous 20 valid tests 4 valid failures in previous 89 valid tests +

Failures for Division III: 2 valid failures in previous 20 valid tests 2 valid failures in previous 96 valid tests *

• I00 valid tests have not been completed on this division.

Number of Valid Failures in Previous 100 Valid Tests of all Diesel Generators at River Bend Station: 2 i

Page 2 of 2

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.;j 4, .ww, GULF STATES UTILITIES COMPANY man w.nw ,a :u c a , ,.,w,.

, ,  :> - .., ,y, September 15,.1989 RBG- 31520 File Nes. G9.5. C9.25.1.4 l U. S. Nuclear Regulatory Commission -

i Document Control Desk ~

Washington, D.C. 20555 l-l Gentlemen

River Bend Station - Unit 1 Decket No. 50-458 Enclosed is Gulf States Utilities Company's Special Report concerning an invalid failure of the Division I' diesel generator  :-

at River Bend Station. This report is being submitted pursuant .

to River Bend Station Technical Specification 4.8.1.1.3 and 6.9.2.

Sincerely,

, f . h-c U. E. Booker Manager-P.iver Bend Oversight River Bend Nuclear Group 9-&'

/

f JEB/TFP/RGW/4HM/KRK/ch i

I cc: U. S. Nuclear Regulatory Commission l Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Resident Inspector Post' Office Box 1051 f St. Francisville, LA 70775  !

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g. ,

SPECIAL REPORT At 2148 on 8/23/89 while performing surveillance testing on the Division I diesel generator (DG), an invalid failure occurred due to a trip from high turbocharger vibration. In accordance with Regulatory Guide 1.108 the following information is provided:

Diesel Generator Unit Designation and Number: Division I, IEGS*EGIA Cause of Failure:

-- At 2148 on 8/23/89, while performing Surveillance Test Procedure (STP)-309-0201, " Diesel Generator Division I Operability Test" to demonstrate the operability of the Division I DG, the DG tripped due to a high vibration signal from the turbocharger vibration trip switch. The DG had been started at 2117, the output breaker was closed at 2122 and the DG was then leaded to 3100 KW (100% load). This trip is categorized as an invalid failure in accordance with Regulatory Guide 1.108 Position C.2.e.(2) since vibration readings taken during the next diesel run, which commenced at 0147 on 8/24/89, were not higher-than baseline readings taken during the first two l

operating cycles (fuel cycles). Also, since vibration trips are L

automatically bypassed in the emergency operating mode of the DG, the actuation of this trip device would not have shut down the unit or rendered it inoperable had it been operating in response to an actual emergency. .

~

The vibration switch which initiated the trip had been installed immediately before the operability run, and had been calibrated during a short duration engine run especially for that purpose. This short run was necessary since the switch is set to trip at a prescribed setting above a background level of normal diesel operation at 100% load. The new switch installation was a follow-up action to a previous vibration trip where the switch was found to l be defective following retest, (reference letter RBG-31090 dated 6/15/89).

1 Past station maintenance records for the diesels were reviewed. Numerous

-instances were found where new switches were defective or became defective after a short operating life. Other utilities which use Enterprise diesel engines with Calecn E4600A vibration switches were consulted and it was reported by those who bench tested the new switches before installation that 50% or more failed. Design Engineering's preliminary conclusion is that the vibration trip was spurious in nature, caused by a defective trip switch.

The mode of failure may be due to leakage of air around the 0-rings in the shuttle valve of the trip switch.

The vibration trip switch was taken out of service, and procedure STP-309-0201 was successfully reperformed. The vibration switch mounted on the engine block remained operative, and will continue to provide protection for the diesel engine. Design Engineering evaluated return of the DG to operable sta tus with the turbocharger vibration switch bypassed, and determined this condition to be acceptable because the vibration switch is j automatically bypassed in the emergency operating mode. '

l l

Page 1 of 2 1

+-

i

(

With the turbocharger vibration trip manually bypassed, the f?llowing parameters will be monitored when the diesel is run:

1. Turbocharger oil pressure

2. Combustion air pressure

3. Turbocharger vibration levels and support integrity 4

4. Turbocharger noise level for any unusual sounds I If any unusual conditions are noted on any of these four parameters, the operators have been instructed to shut down'the DG if it is not operating in the emergency mode.

Corrective Action:

Replacement of the vibration switch is scheduled for the next diesel generator outage. Replacement will include bench testing of the switch to determine its functional reliability prior to installation. Design Engineering has provided Maintenance with a test procedure which exactly duplicates the operation of the vibration switch during engine start, vibration lockout, safety shutdown system activation, vibration trip, and reset.

Current Surveillance Intervals: Division I: Monthly Division II: Monthly ,

Division III: Weekly Test Intervals Conform to Technical Specifications: Yes Failures for Division I: 0 valid failures in previous 20 valid tests 0 valid failures in previous 100 salid tests Failures for Division II: 0 valid failures in previous 20 valid tests 4 valid failures in previous 89' valid tests

• Failures for Division III: 2 valid failures in previous 20 valid tests 2 valid failures in previous 96 valid tests *

• I00 valid tests have not been completed on this division.

Number of Valid Fai'ures in Previous 100 Valid Tests of all Diesel Generators at River Bend Station: 2 Page 2 of 2

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