ML19324B137

LER 89-023-00:on 890922,turbine Trip Occurred on Loss of Power to Four Main Turbine Auto Stop Solenoids.Caused by Failure of Capacitor on Dc to Dc Converter Board in nonsafety-related Inverter.Inverter repaired.W/891023 Ltr

ML19324B137
Person / Time
Site:	South Texas
Issue date:	10/23/1989
From:	Ayala C, Chewning R HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-023, LER-89-23, ST-HL-AE-3270, NUDOCS 8911010105
Download: ML19324B137 (5)

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P.O. Box 1700 lloustosi, Texas 77001 (713) 228 9211 l

October 23, 1989 ST-HL- AE- 3270 File No.: G26 10CFR50.73 U. S. Nuclear Regulatory Commission

Attention: Document Control Desk Washington, DC 20555

! South Texas Project Electric Generating Station Unit 2 Docket No. STN 50-499 Licensee Event Report 89-023 Regarding a Reactor Trip Due to a Turbine Trip Caused by an Inverter Failure Pursuant to 10CFR50.73, Houston Lighting & Power (HL&P) submits the

, attached Licensee Event Report 89-023 regarding a reactor trip due to a turbine trip caused by an inverter failure. This event did not have any adverse impact on the health and safety of the public.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at ($12) 972-8628.

& l R. W. Chewning ,e/ ~

Vice President Nuclear Operations RWC/BEM/eg Attachments LER 89-023, South Texas, Unit 2 l:

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lloudon t.ighting k Power Company i ST-FL-AE 3270 File No.: G26 Page 2 ,

cci Regional Administrator, Region IV Rufus S. Scott .

Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company (

Arlington, TX 76011 P. O. Box 1700 Houston, TX 77001  !

George Dick, Project Manager U. S. Nuclear Regulatory Commission INPO j Washington, DC 20555 Records Center '

1100 circle 75 Parkway l Jack E. Bess Atlanta, GA 30339-3064 Senior Resident Inspector-Unit I c/o U. S. Nuclear Regulatory Commission Dr. Joseph H. Hendrie P. O. Box 910 50 Bellport Lane Bay City, TX 77414 Be11 port, NY 11713 ,

J. I. Tapia D. K. Lacker i Senior Resident Inspector-Unit 2 Bureau of Radiation Control i c/o U. S. Nuclear Regulatory Commission Texas Department of Health '

P. O. Bon 910 1100 West 49th Street Bay City, TX.77414 Austin, TX 78756-3189  ;

J. R. Newnan, Esquire r Newman & Holtzinger, P.C.

1615 L Street, N.W.

Washington, DC 20036 R. L. Range /R. P. Verret Centra! Power & Light Company -

P. O. Box 2121 Corpus Christi, TX 78403 c

R. John Hiner (2 copies)

Chief Operating Officer City of Austin Electric Utility ,

721 Barton Springs Road Austin, TX 78704 R. J. Costello/M. T. Hardt City Public Service Board P. O. Box 1771 San Antonio, TX 78296 Revised 06/16/89 NL.DISR4

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l On September 22. 1989 U it 2 was in Mode 1 at 94 percent power. At 0201 L

hours a turbine trip occurred on loss of power to the four main turbine auto j L stop solenoids. The reactor tripped on the turbine trip. A main feedwater isolation and auxiliary feedwater actuation occurred on low average Reactor j

' Coolant System temperature as expected. The unit was stabilized in Mode 3 i

with no unexpected post-trip transients. The cause of this event was failure l of a non safety-related inverter which interrupted power to the main turbine  :

l auto stop solenoids. A contributing cause was that the design did not provide for the single feilure of a power feed. The inverter has been repaired and returned to service. The power feed design has been changed to add an additional power source.

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f DESCRIPTION OF OCCURRENCE:

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On September 22, 1989, Unit 2 was in Mode 1 at 941 percent power. At 0201 hours0.00233 days <br />0.0558 hours <br />3.323413e-4 weeks <br />7.64805e-5 months <br />, a turbine trip occurred on loss of power to the four main turbine auto  !

stop solenoids. The reactor tripped on the turbine trip. A main feedwater  ;

isolation and auxiliary feedwater actuation occurred on low average Reactor l

Coolant System temperature as expected. The control room operators closed the Hain. Steam Isolation Valves to prevent excessive cooldown. The unit was stabilized in Mode 3 with no unexpected post-trip transients.

The Main Turbine Emergency Trip Cabinet contains the auto stop solenoids which vent turbine trip fluid to initiate a turbine shutdown. These solenoids are  !

normally powered by an inverter through an automatic transfer switch. In the  ;

event of an inverter failure, the automatic transfer switch shifts the power supply to an alternate source: however, this is a break-before-make transf er ,

which results in a momentary loss of power. The transfer does not take place I quickly enough to prevent a turbine trip.

CAUSE OF EVENT:

The cause of this event was the f ailure of a capacitor on the DC to DC converter board in the non eafety-related inverter. A contributing factor was that redundant power feeds were not supplied to the Main Turbine Emergency Trip Cabinet.

ANALYSIS OF EVENT:

Reactor trip and Engineered Safety Features actuation is reportable pursuant to 10CFR50.73(a)(2)(iv). The plant was brought to a stable condition in Mode 3 with no unexpected post-trip transients. No safety injection actuation occurred as a result of this event.

CORRECTIVE ACTION:

The following corrective actions are being taken as a result of this event:

1. The inverter has been repaired and returned to service.

2. The design of the power feeds to the Main Turbine Emergency Trip Cabinet has been changed to add an independant source of power. In the cvent of the loss of power from either source, a turbine trip will not occur.

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.The inverter is a 25 KVA. single phase. 120 volt AC unit manufactured by Elgar Corporation. The model number is INV 253-1-105, i

There have been two previous events reported regarding the failure of this ,

same model of inverter

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LER 88-021 (Unit 1) reported an inverter failure which caused numerous l ESF actuations. )

LER 89-020 (Unit 2) reported an inverter failure which cause the simultaneous tripping of three steam generator feedwater pumps resulting i in a manual reactor trip.

A study has been initiated to address the reliability of the secondary plant 2 in response to the recent Unit 2 trips. This study includes the turbine trip controls.

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