05000245/LER-1978-021-03, /03L-0:on 780914,gas Turbine Tripped While Output Voltage Being Adjusted.Caused by Faulty Gas Generator Speed Switch 3A in Electronic Controls

/03L-0:on 780914,gas Turbine Tripped While Output Voltage Being Adjusted.Caused by Faulty Gas Generator Speed Switch 3A in Electronic Controls

ML20147F628
Person / Time
Site:	Millstone
Issue date:	10/12/1978
From:	Young R NORTHEAST UTILITIES
To:
Shared Package
ML20147F625	List: 05000245/LER-1978-021, Forwards LER 78-021/03L-0 05000245/LER-1978-021-03, /03L-0:on 780914,gas Turbine Tripped While Output Voltage Being Adjusted.Caused by Faulty Gas Generator Speed Switch 3A in Electronic Controls
References
LER-78-021-03L, LER-78-21-3L, NUDOCS 7810200072
Download: ML20147F628 (1)

LER-1978-021, /03L-0:on 780914,gas Turbine Tripped While Output Voltage Being Adjusted.Caused by Faulty Gas Generator Speed Switch 3A in Electronic Controls

Event date:
Report date:
2451978021R03 - NRC Website

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3 60 6l DOCKE' JUMBER 68 69 EVEf4T DATg 74 75 R E POR T D AT E 80 EyENT DESCnlPTioN AND POOS ABLC (,NSEoVENCES h [O_L2J l On September 14, 1978, at 2 l 00 ho~u rs. thil.e Retforclin.g ro u t i no c urvn i l l a nf n. tha li g l gas turbine tripped.uile the output voltage was__beina adiustad.

The gas turbine 1

[O i.tj l was removed from service and the required surveillances were begun (T.S 4.5.F.M.

Oi3j [ While testing the Core Spray System, a leaking flange gasket was detected on Core

'll IO Ic i i Spray 'A' System.

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.CAUSE DCSCRIPTION AND CORRECTIVE ACTIONS h [i [ o j [ Investigation revealed that the trip was caused by a faulty aas aenerator soeed I'

li li ] [ switch 3A, in an electronic control.

The electronic control waJ replaced and the I

[ q 7) { gas turbine was tested and declared operable Sept. 16,1978 at 2215 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.428075e-4 months <br />.

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Attachment to LER 78-21/3L Northeast Nuclear Energy Company Millstone Nuclear Power Station, Unit 1 Provisional License Number DPR-21 Docket Number 50-245 j

IDENTIFICATION OF OCCURRENCE:

The gas turbine generator output breaker inadvertently tripped during surveillance.

CONDITIONS PRIOR TO OCCURRENCE:

j Prior to the occurrence, the unit was operating at a steady state

'l power level of 100 percent.

DESCRIPTION OF OCCURRENCE:

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On September 14,1978, at 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />, while performing routine surveillance, the gas turbine tripped while the output voltage was being adjusted.

Investigation at the gas turbine local control panel revealed an " exciter trouble / power loss" and a " gas generator overspeed alarm."

The gas turbine generator was removed from service and the required surveillance for Automatic Pressure Relief Subsystem, low pressure cooling and a containment cooling was started in accordance with' Technical Specification 4.5.F.3.

While testing the Core Spray System a leaking flange gasket was detected on the Core Spray "A" System.

APPARENT CAUSE OF OCCURRENCE:

1 An investigation was initiated which revealed that the gas turbine trip was caused by a faulty gas generator speed switch.

Limit j

3A, overspeed was found to have a decreasing trip point as the circuitry temperature increase'd.

All other speed limits including the 3B overspded circuit, functioned properly.

ANALYSIS OF OCCURRENCE:

The gas turbine is 01.1 of two emergency power supplies that are utilized for Engineered Safeguard Systems.

The loss of the gas turbine we..uld mean the loss of the feedwater Coolant Injection System, one loop of the low pressure Coolant Injection System and one loop of the Core Spray System. The entire spectrum of accidents has been analyzed with respect to, the loss of either power supply and has been found acceptable.

At the time of the occurrence, during which the gas turbine was inoperable, the other emergency power supply was operable.

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Attachment to LER'78-21/3L - Page 2

, i CORRECT!VE ACTION:

After the inspection of the electronic control associated with the gas generator speed switch,.it was decided to replace the electronic control containing the. limit 3A switch.

The spare electronic control was installed and, tested satisfactorily.

The

- gas turbin'e was tested, returned to service, and declared operational at 2215 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.428075e-4 months <br />, September ~16,1978.

The electronic control that was replaced was manufactured by the l

- Reliance Electric Company, Model No. 927-01-031.

All speed switches will be tested for temperature e.ffect and improved ventilation will be provided.

Additionally, the previously

- j mentioned core-spray leaking flange gaske* was replaced with a flexitallic gasket.

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