ST-HL-AE-5182, Special Rept:On 950823,valid Failure of Sdg 12 Occurred Due to Misalignment of Reset Coil Contacts Resulting in Intermittent Failure of K1 relay.K1 Relay in Sdg 12 Replaced

Special Rept:On 950823,valid Failure of Sdg 12 Occurred Due to Misalignment of Reset Coil Contacts Resulting in Intermittent Failure of K1 relay.K1 Relay in Sdg 12 Replaced

ML20092L639
Person / Time
Site:	South Texas
Issue date:	09/21/1995
From:	Myers L HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-5182, NUDOCS 9509280073
Download: ML20092L639 (4)

Text

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"The Light c o mp a ny outh Texas Project Dectric Generating Station P. O. hm 289 Mworth, Texas 77483 Houston Lighting & Power September 21, 1995 ST-HL-AE-5182 File No.: G02 10CFR50.36(c)(5)

U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 ,

South Texas Project Electric Generating Station Unit 1 Docket No. STN 50498 Special Report Regarding a Valid Failure of Standby Diesel Generator #12 on August 23.1995 Pursuant to the South Texas Project Electric Generating Station Technical Specifications 4.8.1.1.3 and 6.9.2, the South Texas Project submits the attached Special Report regarding the August 23,1995, valid failure of Standby Diesel Generator #12.

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

L.W. Mye s Plant Manager, Unit 1 MKJ/lf

Attachment:

Special Report Regarding Standby Diesel Generator #12 Valid Failure

.) c n n ,s NVUNAd SREP-95\5182 /

Project Manarer on Behalf of the Parthipants in the South Texas Project I 9509280073 950921 I PDR ADOCK 05000498 S PDR

i-i .

Houston Lighting & Power Company ST-HL-AE-5182

- South Texas Project Electric Generating Station - File No.: G02 Page 2 c: 1

Leonard J. Callan Rufus S. Scott  ;

Regional Administrator, Region IV Associate General Counsel )

U. S. Nuclear Regulatory Commission Houston Lighting & Power Company l 611 Ryan Plaza Drive, Suite 400 P. O. Box 61067 j Arlington, TX 76011-8064 .

Houston, TX 77208 Thomas W. Alexion Institute of Nuclear Power j Project Manager Operations - Records Center U. S. Nuclear Regulatory Commission 700 Galleria Parkway Washington, DC 20555-0001 13H15 Atlanta, GA 30339-5957  :

.  : David P. Loveless Dr. Joseph M. Hendrie

- Sr, Resident Inspector 50 Bellport Lane

c/o U. S. Nuclear Regulatory Comm. Bellport, NY l1713 ,

P. O. Box 910 Bay City, TX 77404-0910 Richard A. Ratliff 4

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 i

> U. S. Nuclear Regulatory Comm.

K. J. Fiedler/M. T. Hardt Atto: Document Control Desk City Public Service Washington, D. C. 20555-0001 ]

, P. O. Box 1771 l

!. San Antonio, TX 78296 l J. C. Lanier/M. B. Lee J. R. Egan, Esquire l l City of Austin Egan & Associates, P.C. l Electric Utility Department 2300 N Street, N.W. j

!. 721 Barton Springs Road Washington, D.C. 20037 Austin, TX 78704 p Central Power and Ligk Company J. W. Beck A*ITN: G. E. Vaughn/C. A. Johnson Little Harbor Consultantu, Inc.

P. O. Box 289, Mail Code: N5012 44 Nichols Road Wadsworth, TX 77483 Cohassett, MA 02025-1166 1

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. Attachment ,

ST-HL-AE-5182 '

Page 1 of 2 South Texas Project Electric Generating Station

] Unit 1

' Docket No. STN 50-498 i Special Report Regarding a Valid Failure of j Standby Diesel Generator #12 on August 23.1995 i

DESCRIPTION OF EVENT

i On August 23,1995, Unit I was in Mode 1, at 100% power. During the performance

.of an operability test, Standby Diesel Generator #12 failed to obtain normal voltage and frequency during an emergency-mode start. The engine came up to rated speed, however, there was no indication of generator output voltage.

1 The electro-magnetic K1 device is normally latched in the standby state and requires

! an operate signal to actuate the reset coil, unlatching the K1 to allow for voltage regulator

operation. A lack of this signal, or failure of the reset coil to function will result in the K1 not changing state.

l With the engine running, a visual inspection revealed that the K1 relay was still in the i latched condition. During this inspection, the system engineer tapped on the K1 relay and the attached reset coil case. Shortly after, the generator developed normal output voltage and the K1 was noted to have changed state. The engine was subsequently secured and removed from service. The diesel start attempt was classified as a valid failure, and Standby Diesel

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Generator #12 was declared inoperable.

The Kl relay was replaced and further circuit functional testing was performed with field flash power disabled. Total circuit function was verified through repeated cycles.

Following restoration, the diesel satisfactorily completed a post-maintenance test and subsequent surveillance.

Inspection of the malfunctioning Kl relay revealed pitting and signs of arcing on the i reset coil contacts. The contacts appeared to be misaligned as evidenced by the visual point of contact being on the extreme edges of the contact material and the free side-to-side movement of the movable contact. The mechanical action and auxiliary contacts of the relay i were checked with no abnormalities noted. Other components and connections of the field circuit were checked with no significant anomalie The relay was reassembled, and

electrically cycled several times on the bench with nu malfunctions. The appearance and misalignment of the contacts, and the operation of the device after tapping on the case strongly indicate an intermittent failure of the K1 relay.

Attachment

. ST-HL-AE-5182 Page 2 of 2 CAUSE OF EVENT:

The cause of this event is attributed to the misalignment of the reset coil contacts resulting in an intermittent failure of the K1 relay.

ANALYSIS OF EVENT:

Failure of the K1 relay to operate during the diesel start attempt from emergency-mode resulted in the inability of Standby Diesel Generator #12 to generate output voltage. Standby Diesel Generator #12 was not capable of performing its design function, and as such, Standby Diesel Generator #12 was inoperable. This failure to meet the requirements of Technical Specifications resulted in the start attempt being classified as a Valid Failure.

CORRECTIVE ACTIONS;

1. The K1 relay in Standby Diesel Generator #12 was replaced.

2. The investigation will be finalized addressing the root cause of Standby Diesel Generator #12 Valid Failure.

3. Additional corrective actions, including a vendor developed upgrade of the K1 relay will be evaluated as part of the root cause analysis.

ADDITIONAL INFORMATION:

There have been two valid failures in the last 20 valid tests of Standby Diesel Generator #12. The number of valid failures in the last 100 valid tests is four. Standby Diesel Generator #12 is on increased testing frequency as required by Technical Specifications.