ML19309A363
| ML19309A363 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/04/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19309A359 | List: |
| References | |
| NUDOCS 8003270819 | |
| Download: ML19309A363 (3) | |
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llh ABNORMAL OCCURRENCE REPORT DOCKET No. 50-312-74-1 I
Report Date:
September 4, 1974 Occurrence Date:
August 29, 1974 Time:
1830 Facility:
Rancho Seco Nuclear Generating Station, Unit No. 1, Clay Station, California i
Identification of Occurrence:
Diesel-Generator "B" did not start and attain proper voltage as required by Surve111anca Testing.
i Conditions Prior to Occurrence:
The plant was at refueling shutdown conditions and completing control rod drive coupling.
Description of Occurrence:
1 During the conduct of the monthly Surveillance Test of the "B" Diesel Generator, the diesel engine failed to start on the first three attempts.
i When the engine did start on the fourth attempt, the generator failed to attain proper voltage.
Prior to conducting the test, an operator was stationed locally at the generator. When the control room operator pushed the "B" Diesel 2
start button the engine cranked for 10 seconds and having failed to start, went into lockout automatically as der'gned. Star' ting air was allcwed to return to 200 psig and the lockout was rese The control room then attempted to start the engine two more times.
In each case, after cranking for 10 seconds, the diesel went to lockout. The operator then de-energized and re-energized the D.C. control power concluding that a relay may be malfunctioning. A fourth attempt to start the diesel was successful; however, the generator failed to attain the proper voltage j
and there was no RPM indication. The engine was then shut down pending a technical
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analysis to determine the cause.
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Corrective Action Taken:
A detailed dnspection of the relay tachometer revealed that the-problem was. due to 'a loose connection inside the relay tachometer. All the connections I'
inside the tachometer are soldered. The unit was removed from the control circuitry j
i for-a bench check and test.
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t-v During the bench test it was noted that by moving the relay tachometer unit, improper operation could be initiated.
It was also determined that a D.C. voltage high temperature dropping resistor raised the internal temperature of the relay tachometer assembly to approximately 160*F.
All solder connections were resoldered and the resistor moved outside the assembly. The unit was reinstalled. The diesel was then tested and functioned satisfactorily.
4 Designation of Apparent Cause: Component Failure i
Analysis of Occurrence:
The Diesel Generator did not produce voltage due to the failure I
of the relay tachometer which controls the initial energization of the generator field winding.
The control logic for initially energizing the Diesel Generator field during a startup is as follows:
1.
The Diesel Generator start pushbutton is depressed.
2.
The engine begins to accelerate.
3.
The relay tachometer senses when the generator speed is above 400 RPM and closes a contact which energizes f ~sg the gcuerator field winding.
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As the generator accelerates to its rated speed of j
900 RPM, the voltage regulator controls the generator voltage at approximately 4160 volts, the normal operating voltage.
The failure that occurred during the Surveillance Test prevented the relay tachemeter logic from closing the'400 RPM contact. Therefore, the field-windings were not energized and the generator did not produce any voltage.
No apparent cause for the diesel failing to start was found.
Following repair of the relay tachometer, the diesel was started daily August 31 through September 3, 1974. On each attempt the "B" Diesel Engine started on the initial cranking period.
l Equipment I.D.:
The Diesel Generator is a Bruce, C.M. Diesel, Type G886B' rated at 2750 KW.
The tachometer made by Dynalco Corporation, Type RT2450 with a frequency range of 0 to 5300 Hertz.
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f Action Required to Prevent a Peoccurrence:
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i All solder joints in the relay tachot eter were resoldered and the high' temperature resistor moved outside of the tachometer housing. This same modification will be made to the "A" Diesel Generator.
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Failure Data:
This is the first failure of the relay tachometer since the operating license was issued.
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