NOC-AE-000222, Special Rept:On 980614,nonvalid Failure of Standby Diesel Generator Occurred.Caused by Inadequate Procedure.Failed Potential Transformer Was replaced,B-train 4.16 Kv ESF Switchgear Was Reenergized & Procedure Was Revised

Special Rept:On 980614,nonvalid Failure of Standby Diesel Generator Occurred.Caused by Inadequate Procedure.Failed Potential Transformer Was replaced,B-train 4.16 Kv ESF Switchgear Was Reenergized & Procedure Was Revised

ML20236P557
Person / Time
Site:	South Texas
Issue date:	07/09/1998
From:	Parkey G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NOC-AE-000222, NOC-AE-222, NUDOCS 9807170019
Download: ML20236P557 (5)

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l July 9, 1998 NOC-AE-000222 File No.: G02 l 10CFR50 STI: 30659124 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project ,

Unit 1 Docket No. STN 50-498 4 Special Report Regarding a Nonvalid Failure of Slandby Diesel Generator 12 on June 14.1998 Pursuant to South Texas Project Technical Specifications 4.8.1.1.3 and 6.9.2, the STP Nuclear Operating Company submits the attached Special Report regarding nonvalid failure of Standby Diesel Generator 12 on June 14,1998.

If you have any questions on this matter, please contact Mr. K. J. Taplett at (512) 972-8416 or me at (512) 972-7800.

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G. L. Parkey Plant Manager, Unit 1 KJT/

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Attachment:

Special Report Regarding a Nonvalid Failure of Standby Diesel Generator 12 on June 14,1998 9807170019 980709 PDR ADOCK 05000498 6 PDR c:\wpinl\nrc-wkWep-980222. doc

l NOC-AE-000222 File No.: G02 Page 2 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'c Street, Suite 700 Arlington, TX 76011-8064 San Antonio, TX 78205-3692 Thomas W. Alexion Institute of Nuclear Power Project Manager, Mail Code 13113 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 ofIIealth l 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 llouston Lighting & Power Co.

l 1800 M. Street, N.W. P. O. Box 1700 l 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, D.C. 20555-0001 721 Barton Springs Road Austin,TX 78704

, Attachment NOC-AE-000222 File No.: G02 Page 1 of 3 v

Special Report Regarding a Nonvalid Failure of Standby Diesel Generator 12 on June 14,1998 Description of Event:

On June 14,1998 at 2148 hours0.0249 days <br />0.597 hours <br />0.00355 weeks <br />8.17314e-4 months <br />, Standby Diesel Generator 12 was started to reenergize the B-train 4.16 kV Engineered Safety Features Switchgear. The Standby Diesel Generator was started to restore power to the B-train switchgear because the normal power supply had been isolated due to a potential transfonner failure in the switchgear. After a successful Standby Diesel Generator 12 start and output breaker closure reenergizing the B-train 4.16 kV Engineered Safety Features Switchgear, the supply breakers to the 480 VAC load centers ElB1 and ElB2 could not be closed. The unavailability of the 480V load centers prevented supplying Standby Diesel Generator 12 with cooling water. Standby Diesel Generator #12 was secured to prevent overheating. After Standby Diesel Generator 12 was secured, the supply breakers to the 480 VAC load centers ElB1 and ElB2 were able to be closed.

The B-train 4.16 kV Engineered Safety Features Switchgear had been deenergized earlier in response to smoke issuing from the switchgear. The smoke was due to an internal fault in a potential transformer. When the switchgear was deenergized, the load sequencer responded as designed. However Standby Diesel Generator 12 did not start because it had been placed in Pull-To-Stop to allow de-energization of the switchgear. The other B-train 4.16 kV Engineered Safety Features loads were placed in Pull-To-Lock per operating procedures. With the faulty potential transformer isolated, Standby Diescl Generator 12 was taken out of Pull-To-Stop which allowed it to start from the previous load sequencer start signal. When the diesel generator output breaker closed, the load sequencer started its timing functions and closed the timed maintained contacts used for loading the switetgear. However, since the control switch for each load was in Pull-To-Lock, no loads energized. As designed, the start signals from the load sequencer remained applied to all components, including the supply breakers to the 480 VAC load centers ElBI and ElB2.

An attempt was made to load the switchgear manually. When the control switches for the supply breakers to the 480 VAC load centers ElB1 and ElB2 were taken from the Pull-To-Lock to the CLOSE position, the switches passed through the TRIP position. This applied a trip signal to the supply breakers. With a start signal from the load sequencer and a trip signal generated by the  ;

handswitch manipulation, a breaker anti-pump feature associated with the 480 VAC load center l feeder breakers prevented the breakers from closing. The load sequencer and breaker controls operated as designed for this sequence of events.

caw /ml\nrc-wk\srep-98\0222. doc

. i C Attachment NOC-AE-000222 File No.: G02

. Page 2 of 3 Following the replacement of the failed potential transformer, power was restored to the B-train 4.16 kV Engineered Safety Features Switchgear from the normal power supply. The Standby l

Diesel Generator 12 was unavailable to perform its safety function for approximately 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> and 28 minttes.

Cause of Event:

The cause of this event was due to an inadequate procedure because of a lack of knowledge on how the 480 VAC circuit breakers behaved in the circumstances described in this event. The procedure for loss of a 4.16KV bus provided instructions for restoration of the bus which were not compatible with plant design.

Event Analysis:

The B-train 480V load center supply breaker control circuitry operated as designed for the l condition described in this report. It was determined that the B-train 480V load center supply ,

breakers would have shut to energize their loads in response to an emergency condition from a l l normal Engineered Safety Features standby condition. Since the diesel generator, load sequencer, and supply breaker controls operated as designed and no equipment malfunctions occurred, the South Texas Project considers this event as a nonvalid failure attributed to operating error per position c.2.e. (2) of Regulatory Guide 1.108, dated August 1,1977," Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants".

This event had no impact on testing frequency of Standby Diesel Generator 12 since it was classified as a nonvalid failure. The testing fn:quency will remain at 31 days per the South Texas ;

Project Technical Specifications. For Standby Diesel Generator 12, there have been no Valid l Failures in the last 20 Valid Tests and three Valid Failures in the last 100 Valid Tests.

Corrective Actions:

1. The failed potential transformer was replaced.

2. The B-train 4.16 kV Engineered Safety Features Switchgear was reenergized from i the normal offsite power supply.

3. Procedure OPOPO4-AE-0001 " LOSS OF ANY 13.8KV OR 4.16KV BUS" will be revised by September 1998.

c:\wp\nl\nrc-wkwep 98W222. doc

Attachment NOC-AE-000222 File No.: G02

. Page 3 of 3 AdliitionalInformation:

Planned actions related to this event are:

. Submission of a proposal to the Plant Change Committee to improve the control switch circuitry design.

• Submission of a proposal to the Operations Curriculum Review Committee to incluue the lessons learned from this event in the operator training program, e Review the generic implications of this event in accordance with the corrective action program.

7 The Standby Diesel Generator 12 is a Cooper-Bessemer model KSV-20 engine rated at 5500 KW.

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