ML20085M607

RO 50-267/75/13:on 750911,fan Start Relay for 480-volt Tansformer 1B Failed.Caused by Component Failure & Design Flaw.Relays Replaced W/Better Application & Relay Logic Circuitry Reversed Requiring Deenergized Relay

ML20085M607
Person / Time
Site:	Fort Saint Vrain
Issue date:	10/09/1975
From:	Hillyard H, Lambert D, Swart F PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085M605	List: ML20085M602 ML20085M607
References
RO-50-267-75-13, NUDOCS 8311090048
Download: ML20085M607 (3)

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ls REPORT DATE: October 9,1975 UNUSUAL EVENT 75/13 Page 1 of 3 OCCURRENCE DATE: September 11, 1975 FORT ST. VRAIN NUCLEAR GE'NERATING STATION ~

PUBLIC SERVICE COMPANY OF COLORADO . $

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P.O. Box 361 PLATTEVILLE, COLORADO 80651 ep'4

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REPORT No. 50-267/75/13

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IDENTIFICATION OF

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OCCURRENCE: '# ~

Failure ,of the fan start relay for 480 V Transformer 1B. This is identified l as an Unusual Event per Section 7.6 paragraph of the Technical Specifications.

CONDITIONS PRIOR ,

_TO OCCURRENCE: Steady State Power Rotitine Shutdown

, Hot Shutdown Routine Load Change Cald Shutdown X Other (specify)

Refueling Shutdown ' None specified because conditions varied and did not contribute to Routine Startup the failure The major plant parameters at the time of the evhnt were as follows:

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Power RTR

• FMt;h ELECT *

• FMe Secondary Coolant Pressure

• psig Temperature *

'F Flow *

1. /hr.

Primary Coolant Pressure

• psig Temperature- *

• F Core Inlet

• F Core Outlet Flow *

'#/hr. ~

• Not listed since they have no bearing on problem.

8311090048 751013 PDR ADOCK 05000267 S

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UNUSUAL EVENT 75/13 Page 2 o f 3 DESCRIPTION OF OCCURRENCE:

On 8/27/75, it was reported by the plant operating personnel that 480 V -

transformer 1B cooling fans failed to start, either automatically on high temperature, or by manual operation of fan start hand switch. Operations personnel determined by local indication that the cooling fans were necessary in order to continue operation with the existing transformer load requirements. In order to prevent damage due to overheating, it was necessary to replace the fan start relay on an emargency basis. The fans returned to-normal operation with replacement of the relay.

APPARENT CAUSE OF OCCURRENCE: X Design Unusual Service Cond. '

Including Environ.

Manufacture X Component Failure Installation /Const. Other (specify)

Operator Procedure ANALYSIS OF .

OCCURRENCE: ,

A search of essential 480 V transformer maintenance records was conducted. From this search it was noted that a history existed of . trouble with this particular con trol.

On September 11, 1975, an analysis an'd test 'of the fan control schere was c'ompleted.

The results of this study was that the control scheme was unsatisfactory in three respects: , ,

1) Wa type relay used to actuate the cooling fans had a tendency to h'ang up with slight cljanges in orientation.

2) ne start circuit relay logic was undesireable in that it was necessary to energize the relay to start the fans.

3) Failure of the fans to start on high transformer temperature was .not alarmed in the control room.

CORRECTIVE -

ACTION:

For the five n'ir cooled 480 V transformers (3 essential and 2 non essential):

1) ne unsuitable relays will be replaced with a better application.

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, .. ... . a . _ . . x, . . . . . , . . . . _ . . .'d e4e UNUSUAL EVENT 75/13

,. Page 3 of 3

2) 'Ihe relay logic circuitry will be reversed so that it requires a

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de-energized relay to start the cooling ' fans. -

3) An alarm on high temperature will be installed in the control room.

4) The local handswitches will be rewired to bypass the fan start relay and start the fans directly.

'1hese corrective actions have already been completed for 480 V Transformfer 1B.

FAILURE DATA /SDfILAR REPORTED OCCURRENCES 1 ,

None PROGRAFBfATIC UIPACT: ,

None CODE DIPACT:

Nonc -

Submitted By: td. A Harvey W.[billyar( Jr.

Technical Services Supervisor Reviewed By: g4 .

Duane L. Lambert [

Supervisor, Denver Plant, Electricians ,

Approved By: , ; ., _y , $ , _. .

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F[ederic E. Swart Superintendent, Nuclear Production J

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