ST-HL-AE-5393, Special Rept:On 960130,standby DG 11 Valid Failure Caused by Failed op-amp IC Chip on Preposition Board.Voltage Regulator & Preposition Board Replaced

Special Rept:On 960130,standby DG 11 Valid Failure Caused by Failed op-amp IC Chip on Preposition Board.Voltage Regulator & Preposition Board Replaced

ML20117K586
Person / Time
Site:	South Texas
Issue date:	06/06/1996
From:	Myers L HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-5393, NUDOCS 9606110387
Download: ML20117K586 (5)

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Th6 Light c o mp a ny llouston Lighting & Power out h Texas Pmject Ecctric Genuating Station P.O. Box 289 Wadmonh, Texas 77483 June 6, 1996 ST-HL-AE-5393 File No.: G02 10CFR50 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 South Texas Project Unit 1 i

. Docket No. STN 50-498  !

Revision to Special Report Regarding i

Standbv Diesel Generator 11 Valid Faihgg Pursuant to the South Texas Project Technical Specifications 4.8.1.1.3 and 6.9.2, the South Texas Project submits the atteched revision to Special Report regarding a Standby Diesel Generator 1i valid failure which occurred on January 30,1996. Titis revision includes the results of the failure analysis report.

1 If you should have any questions on this matter, please contact Mr. S.M. Head at (512) 972 7136 or myself at (512) 972-7239.

l L.W. Myers Plant Manager, Unit 1 9606110387 960606 '

PDP ADOCK 05000498 S PDit MKJ/mj

Attachment:

Revision to Special Report Regarding Standby Diesel Generator 11 Valid Failure p/

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Monton Lighting & Power Company ST-HL-AE-5393 South Texas Project Electric Generating Station File No.: G02 Page 2 Leonard J. Callan Rufus S. Scott Regional Administrator, Region IV Associate General Counsel U. S. Nuclear Regulatory Commission Houston Lighting & Power Company 611 Ryan Plaza Drive, Suite 400 P. O. Box 61067 Arlington, TX ' 76011-8064 Houston, TX 77208 1 Thomas W. Alexion Institute of Nuclear Power l 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 Dr. Joseph M. Hendrie  ;

Sr. Resident Inspector 50 Bellport Lane I c/o U. S. Nuclear Regulatory Comm. Bellport, NY 11713 P. O. Box 910 )

Bay City, TX 77404-0910 Richard A. Ratliff l Bureau of Radiation Control )

J. R. Newman, Esquire Texas Department of Health  ;

Morgan, Lewis & Bockius 1100 West 49th Street 1800 M Street, N.W. Austin, TX 78756-3189 Washington, DC 20036-5869 U. S. Nuclear Regulatory Comm.

M. T. Hardt/W. C. Gunst Attn: Document Control Desk City Public Service Washington, D. C. 20555-0001 P. O. Box 1771 San Antonio, TX 78296 ,

J. C. Lanier/M. B. Lee J. R. Egan, Esquire City of Austin Egan & Associates, P.C.

Electric Utility Department 2300 N Street, N.W.

721 Barton Springs Road Washington, D.C. 20037 Austin, TX 78704 Central Power and Light Company J. W. Beck ATTN: G. E. Vaughn/C. A. Johnson Little Harbor Consultants, Inc.

P. O. Box 289, Mail Code: N5012 44 Nichols Road Wadsworth, TX 77483 Cohassett, MA 02025-1166

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l l l Attachment i ST-HL-AE-5393 l Page 1 of 3  !

. South Texas Project Unit 1 l Docket No. STN 50-498 Special Report Regarding 1 Standby Diesel Generator 11 Valid Failure I i

l DESCRIPTION OF EVENT l

l On January 30,1996, at 1811 hours0.021 days <br />0.503 hours <br />0.00299 weeks <br />6.890855e-4 months <br />, while Unit I was in Mode 1, Standby Diesel Generator 1I was started for performance of a Standby Diesel Generator Operability l

[ test surveillance following maintenance activities. Voltage increased to 4600 VAC, I exceeding the expected emergency mode setting of 4160 VAC. The diesel was released from the emergency mode to allow for manual control. The operator j attempted to lower the voltage with no success, and subsequently secured the diesel. j Static checks performed on the voltage sensing network, the field flash circuit, and the voltage regulator circuit did not reveal an immediate cause for the apparent loss of '

voltage control. A comprehensive test plan was developed which included installation ,

of recorders for monitoring specific parameters. A malfunctioning voltage regulator I l module was indicated as the most probable cause of the problem, and was replaced. A test run was then performed. To support this test, justification for limited no-load operation at 4600 VAC for data collection was obtained through Design Engineering in coordination with the vendor, NEI Peebles Inc.

j On January 31,1996, at 1458 hours0.0169 days <br />0.405 hours <br />0.00241 weeks <br />5.54769e-4 months <br />, Standby Diesel Generator 11 was started in the emergency mode for testing purposes. Voltage indication exceeded 5250 VAC both in i

the control room and at the local panel meters. The diesel was immediately secured.

The troubleshooting team reconvened to evaluate the recorder traces captured during the start and determine the best course of action for repair. Analysis of the symptoms indicated that the instantaneous preposition board was the next most probable cause.

The instantaneous preposition board was then replaced.

On January 31,1996, at 2059 hours0.0238 days <br />0.572 hours <br />0.0034 weeks <br />7.834495e-4 months <br />, Standby Diesel Generator 11 was started in the test mode for testing purposes. Voltage built to the expected level for the new regulator and preposition beard. Adjustments were made satisfactorily to the regulator and the preposition board to bring voltage to design levels. Two subsequent emergency mode starts and a surveillance test were performed with satisfactory voltage response.

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Attachment ST-HL-AE-5393 Page 2 of 3 DESCRIPTION OF EVENT: (continued) l The removed voltage regulator module and preposition board were sent to the vendor for root cause determination. The vendor determined that the op-amp IC chip on the preposition board was faulty. No cause could be determined for the chip failure. A l secondary anomaly was noted on the voltage regulator module with intermittent wiper contact resistance on the Voltage Range Adjust Potentiometer, 'R4'. This secondary condition was determined to not be related to the failure of the preposition board. The vendor has determined that the preposition board was responsible for both start failures during this event.

CAUSE OF EVENT

h The cause of this event has been determined to be a failed op-amp IC chip on the j preposition board.

ANALYSIS OF EVENT:

4 This event was classified as a Valid Failure. With the mode of failure demonstrated during the maintenance run, the diesel would not have been able to perform its safety related function if challenged.

f CORRECTIVE ACTIONS:

l. Troubleshooting of Standby Diesel Generator 11 was conducted, which resulted in the replacement of the voltage regulator and the preposition board.

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2. The failed voltage regulator and preposition board were sent offsite for failure

analysis, i

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T Attachment ST-HL-AE-5393 Page 3 of 3 ADDITIONAL INFORMATION:

The instantaneous preposition circuit is a discrete board consisting of five resistors, a j potentiometer, an operational amplifier, and a relay. Its function is W allow use of an I adjustable voltage reference for test-mode parallel operation, rnd an instantaneous set I voltage reference for emergency mode operation, l i

An upgrade to the preposition board has been made available from NEI Peebles.

Improvements to the board include replacement of the board mounted relay with a i

solid-state equivalent, and replacement of the op-amp with an updated chip. Plans are currently underway to coordinate replacement of all existing preposition boards with the upgraded models.

An upgrade to the voltage regulator module has also been made available from NEl i Peebles in response to industry problems with the original R4 potentiometer, and a recent Part 21 issued against the component. Currently, spare modules on site and at 1

the vendor facilities are being upgraded. Plans are underway to coordinate the

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upgrade and replacement of all voltage regulator modules installed on site.

l l l Standby Diesel Generator 11 has a previous Valid Failure classification that was attributed to a failure of the preposition board (reference Special Report ST-HL-AE-4604). On September 19,1993, Standby Diesel Generator 1I was started in the

, emergency mode for surveillance testing, and generator voltage built to only 2900 VAC. Subsequent troubleshooting isolated the preposition board as the root cause, l l The preposition board was replaced and the diesel was tested satisfactorily and

returned to service. Failure analysis conducted by the vendor confirmed that the faulty component was the preposition board op-amp. There have been no valid failures from

preposition board malfunctions experienced on other Standby Diesel Generators at the South Texas Project. 1 Previous to this Valid Failure, there had been no Valid Failures in the past 20 valid  ;

tests, and 3 failures in the past 100 valid tests for Standby Diesel Generator 11.

l Therefore, the testing frequency of Standby Diesel Generator 11 continues to be monthly.  ;

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