NOC-AE-000119, Special Rept:On 980307 & 10,non-valid Failures of Standby Generator 13 Occurred.Caused by out-of-calibration Reverse Power Relay Inadequate Work Procedures Used to Calibrate Relay.Procedures Revised

Special Rept:On 980307 & 10,non-valid Failures of Standby Generator 13 Occurred.Caused by out-of-calibration Reverse Power Relay Inadequate Work Procedures Used to Calibrate Relay.Procedures Revised

ML20216A967
Person / Time
Site:	South Texas
Issue date:	04/06/1998
From:	Parkey G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NOC-AE-000119, NOC-AE-119, NUDOCS 9804130338
Download: ML20216A967 (5)

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April 6,1998 NOC-AE-000119 File No.: G02 l 10CFR50 I

U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Unit 1

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Docket No. STN 50.-498  !

Special Report Regarding a Non-Valid Failure of Standby Diesel Generator 13 on March 7.1998 and a Valid Failure on March 10.1998 l Pursuant to South Texas Project Technical Specifications 4.8.1.1.3 and 6.9.2, the South Texas Project submits the attached Special Repon regarding a non-valid failure of Standby Diesel Generator 13 on March 7,1998 and a valid failure on March 10,1998. The corrective actions in the attachment are the licensing commitments in this report.

If you should have any questions on this matter, please contact either Mr. S. M. Head at (312) 972-7136 or me at (512) 972-7800.

I G. L. Parkey I

. . Plant Manager, 3 l "WJ Unit 1 i

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9804130338 980310 PDR ADOCK 05000498 l S

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Attachment:

Special Report Regarding a Non-Valid Failure of Standby Diesel Generator 13 on March 7,1998 and a Valid Failure on March 10,1998 I

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ST-NOC-AE-000119 File No.: G02 Page 2 l Ellis W. Merschoff Jon C. Wood Regional Administrator, Region IV Matthews & Branscomb U. S. Nuclear Regulatory Commission One Alamo Center 611 Ryan Plaza Drive, Suite 400 106 S. St. Mary's Street, Suite 700 Arlington, TX 76011-8064 San Antonio, TX 78205-3692 Thomas W. Alexion Institute ofNuclear Power Project Manager, Mail Code 13H3 Operations - Records Center U. S. Nuclear Regulatory Commission 700 Galleria Parkway Washington, DC 20555-0001 Atlanta, GA 30339-5957 David P. Loveless Richard A. Ratliff Sr. Resident Inspector Bureau of Radiation Control c/o U. S. Nuclear Regulatory Commission Texas Department of Health P. O. Box 910 1100 West 49th Street Bay City, TX 77404-0910 Austin, TX 78756-3189 J. R. Newman, Esquire D. G. Tees /R. L. Balcom Morgan, Lewis & Bockius Houston Lighting & Power Co.

1800 M. Street, N.W. P. O. Box 1700 Washington, DC 20036-5869 Houston,TX 77251 M. T. Hardt/W. C. Gunst Central Power and Light Company City Public Service ATTN: G. E. Vaughn/C. A. Johnson P. O. Box 1771 P. O. Box 289, Mail Code: N5012 San Antonio,TX 78296 Wadsworth,TX 77483 A. Ramirez/C. M. Canady U.S. Nuclear Regulatory Commission City of Austin Attention: Document Control Desk Electric Utility Department Washington, DC 20555-0001 721 Barton Springs Road Austin,TX 78704

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' NOC-AE-000119 j Page 1 of 3 '

Attachment Special Report Regarding a Non-Valid Failure of Standby Diesel Generator 13 on March 7,1998 and a Valid Failure on March 10,1998 l

Description Of Events On March 7,1998, Standby Diesel Generator 13 was being run for a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> surveillance test.

While loaded at 110% as required by the test, the output breaker tripped open. Indication of the trip was a transformer reverse power condition. The associated 67/50D reverse power relay is for transformer protection and functions to prevent excessive current flow from the diesel through the 4 transformer and back to the grid. Troubleshooting determined that reverse power relay 67/50D

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was out of calibration (setpoint was approximately 700A instead of the required 1008A). The  ;

relay was recalibrated and Standby Diesel Generator 13 successfully completed its 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run on March 10,1998.

The investigation regarding the out of calibration reverse power relay determined the most probable cause was improper isolation of the relay during the calibration activity. This relay was last calibrated in September 1997. It was found that information regarding the method to l effectively isolate the relay was not translated into work documents. '

I The 67/50D relay is used to trip open the diesel generator output breaker on excessive current l from the 4160 ElC Emergency Safety Features (ESF) bus to the ESF transformer (13.8kV to 4160VAC) to protect the transformer. During standby diesel generator emergency operation for a loss of offsite power or a loss of offsite power with safety injection condition, the normal supply breaker from the ESF transformer to the 4160VAC bus is automatically stripped prior to the l standby diesel generator closing onto the 4160VAC bus. Since the transformer is disconnected during standby diesel generator emergency operation, there is no current flow for the 67/50D device to detect in this condition. Even with the low miscalibration for this device, it would not trip open the standby diesel generator output breaker during emergency operation. The trip that occurred with Standby Diesel Generator 13 during testing on March 7,1998 would not have occurred during the emergency mode of operation. The South Texas Project conforms to Revision 1 of Nuclear Regulatory Commission Regulatory Guide 1.108, " Periodic Testing of Diesel Generator Units used as Onsite Electric Power Systems at Nuclear Power Plants". Per position C.2.e.(2) of that guide, this occurrence is classified as a Non-Valid Test and Non-Valid l Failure because the output breaker trip can be attributed to malfunction of equipment that is not operative in the emergency operating mode. Therefore, there is no impact on surveillance testing frequency requirements.

Standby Diesel Generator 13 was inoperable for approximately 32 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br /> following the reverse power relay problem.

eAwpW\nrc-ap\srep-92W10119 doc S11: 30578284

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, , Attachment NOC-AE-000119 Page 2 of 3 On March 10,1998, Standby Diesel Genera m n as started for an 18 month fast restart surveillance following the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run surveillana wenty seconds after a successful emergency mode start, the diesel generator tripped on low-low lube oil pressure. Standby Diesel Generator 13 was declared inoperable. The source of the trip was traced to the turbocharger low-low lube i

oil pressure switches. These switches failed to reset from a tripped condition in the required time following the Standby Diesel Generator 13 hot restart, even though actual turbocharger lube oil pressure was developed normally during the start. The switches were checked for correct calibration and were found to be set satisfactorily. The oil removed fram the sensing line for the turbocharger lube oil pressure switches during troubleshooting was filtered and several small pieces of gasket material were found. It was also discovered that the normal calibration process

j. leaves a small amount of trapped air in the sensing line. It is believed that the foreign material L slowed the rate at which the lube oil could compress the air trapped in the sensing line, effectively l

delaying the sensed nil pressure increase on a diesel start (sensed oil pressure was satisfactory in steady-state operation). Sensed oil pressure must achieve normal operating pressure in less than 20 seconds following a start to avoid a trip on low-low lube oil pressure.

It could not be determined when the foreign gasket material could have entered the sensing line, l but it is believed this occurred some time in the distant past. Station improvements in foreign

! material exclusion practices in recent years should preclude this condition from occurring in the j future. In addition, planned procedure changes to require displacing stagnant lube oil from the l sensing lines during future pressum switch calibrations will assist in maintaining the lube oil free

t. of foreign material.

l The turbocharger lube oil prat.ure sensing line was flushed and then vented utilizing standby lube

oil pressure to purge air from the sensing line. Foitowing this, a loaded run surveillance and the  ;

l hot restart test were satisfactorily completed on March 13,1998. l l

The turbocharger low-low lube oil pressure switches function in the emergency mode to protect

! the diesel generator from catastrophic failure should the lube oil system not achieve or maintain sufficient oil pressure following an emergency start signal. While the actual lube oil pressure was l

satisfactory throughout engine operation during this event, the spurious low-low lube oil pressure trip due to the undesired time delay in the pressure sensing line prevented the standby diesel generator from performing its design function on the initial hot restart test. For this reason, this event was classified as a Valid Failum.

Including this Valid Failure, Standby Diesel Generator 13 has had two 1/alid Failures in the last 20 I Valid Tests, two Valid Failures in the last 50 Valid Tests, and three Valid Failures in the last 100 Valid Tests. Since two Valid Failures in the past 20 Valid Tests exceeds the Technical Specification trigger value, testing frequency has been increased from monthly to at least once per seven days.

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Attachment NOC-AE-000119 Page 3 of 3

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Standby Diesel Generator 13 was inoperable for approximately 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br /> following the turbocharger low-low lubd oil pressure sensing condition.

Cause Of Events t

l The most probable cause of the Standby Diesel Generator output breaker trip due to an out-of-calibration reverse power relay was inadequate work procedures used to calibrate the relay. )

! The cause of the Standby Diesel Generator 13 low-low lube oil pressure trip was foreign material L in the turbochargerlube oil pressure switches sensing line with a contributing cause being air in ,

l the sensing line. I Corrective Actions l

1. The Standby Diesel Generator 13 67/50D relay was recalibrated and the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> surveillance run was successfully completed.

2. Standby Diesel Generators 11 and 12 were started and loaded successfully to demonstrate no common mode failure mechanism existed.

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3. The 67/50D relays for the other standby diesel generators in both Units were visually  ;

verified to have the appropriate dial setting for the correct setpoint. 1 i

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i The turbocharger low-low lobe oil pressure switch sensing line was flushed and then - '

vented to minimize entrapped air. - Following this, a loaded run surveillance and a hot restant test were successfully performed.

5. Actions to prevent condition recurrence are:

i e Procedures for calibrating the reverse power relay will be revised by June 1998.  !

• The diesel turbocharger low-low pressure trip calibration procedure will be revised by July 1998 to include displacing stagnate lube oil and identifying the proper location for purging air from the sensing lines following calibration.

AdditionalInformation The Standby Diesel Generator is a Cooper-Bessemer model KSV-20 engine rated at 5500 KW, cAwp%hnrc-apwep-98\000119. doc STl; 30578284