ML20082C216
| ML20082C216 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 03/31/1995 |
| From: | Boyce R PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9504060231 | |
| Download: ML20082C216 (3) | |
Text
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Robert CL Boyes ~
.Ptant Manager 5-M Urnerick Generating Station rK ;
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PECO ENERGY g=";TergLn
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PO Box 2300 -
Sanatoga, PA 19464M20.
a 215 3271200 Ext,2000 a
4 March 31, 1995 Docket Nos. 50-352
@0-353 License Nos. NPF-39 NPF-85 U.
S. Nuclear. Regulatory Commission Attn ~ Document Control Desk Washington, DC 20555
Subject:
Limerick Generating Station, Units 1 and 2 Information.Regarding Malfunction or Degradation of Agastat Relays on the Onsite 4 kV AC Safeguard Power System During the third refueling outage for Limerick Generating Station Unit 2, two (2) Agastat relays malfunctioned and a third was found'to be degraded during surveillance testing of the onsite 4 kV AC safeguard power system.
The relays are designed to de-energize on a. loss of. power to the associated 4-kV division and initiate logic to start.the corresponding emergency. diesel ~
generator and other safety functions.
Although'the three (3) conditions were determined to be not' reportable, it was concluded
.that the information should be shared with the NRC and the industry due to the potential safety significance of these conditions.
The attachment to this letter provides.the results of the investigation into the cause and corrective actions for.
these conditions.
If you have any questions or require any additional information, please contact us.
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'DBN:cah Attachment cc:
T. T. Martin, Administrator, USNRC, Region I N. S. Perry, USNRC Senior Resident Inspector, LGS Ny@\\
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9504060231,950331.
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-Page 1-of 2 Docket Nos.-50-352 50-353
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s Limerick Generating Station
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on or Degradation of Agastat Relays on The Onsite'4 kV AC-Safeguard Power System During the third refueling outage for. Limerick Generating Station (LGS) Unit 2, conducted during February, 1995,tsurveillance-testing was performed on the four (4) Unit 2 onsite 4-kV AC-safeguard power divisions.
These tests arefrequired by the Technical Specifications and include a simulated Losslof Offsite Power (LOOP) condition on each individual safeguard bus to test the dead bus relays and. associated circuits.
The dead bus relays monitor the 4 kV bus voltage and de-energize on a loss of power, closing contacts to energize DC powered auxiliary relays.
The-auxiliary relays start the associated Emergency Diesel Generator a
(EDG) and. initiate a load shed.
During the outage testing,;two (2) of the four (4) dead bus relays failed to properly function and the associated EDG did not start on a simulated LOOP condition.
Also, a third relay was found-to be degraded'duringJa 1
preventive maintenance inspection that was performed prior to the LOOP tests.
These relays are manufactured by Agastat, model.
number EGPI.
The three (3) relays'were immediately replaced and the tests were then performed satisfactorily.
The failure analysis of the first two (2) relays. identified that-the relays malfunctioned due to oxidation of-the relay contacts causing high contact resistance when the relay de-energized.
These relays are normally energized and the contacts associated with the auxiliary relays are maintained open.
These contacts-are seldom closed and as a result, oxidation was able to develop, even through the relay has a cover and is located in a switchgear enclosure in a mild environment.
The only previous similar failure at LGS occurred on'the Unit 2 D22 EDG in' March of 1993.
The failure analysis of the third relay identified a-degraded relay coil that is unrelated to the contact oxidation failure F
mode.
This relay was replaced as a conservative measure.
-There have been no previous similar relay coil concerns identified at i
LGS.
To. ensure that the four (4) Unit 1 dead bus relays were functional, the relays were replaced with new relays on March 9, 1995.
Each of~the removed relays was then tested in a. laboratory simulating field conditions and each relay functioned properly.
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t Attachment Page 2 of 2 Docket Nos. 50-352 50-353 To ensure that the eight (8) dead bus relays installed in the Unit 1 and Unit 2 EDGs continue to be capable of functioning, each relay will be tested on an accelerated schedule (currently once every six (6) weeks) to avoid the build up of oxidation on the contacts.
Additional information gathered during the investigation identified that the three (3) relays were manufactured in 1987, in three (3) different weeks over a fifteen (15) week span.
A review of the seventy eight (78) related industry events reported on the Nuclear Network identified ten (10) relay failures related to normally energized Agastat relays.
None of the industry failures were associated with the identical application as LGS.
These relay conditions have been added to the LGS relay performance monitoring program.
An analysis is being performed to determine the appropriate testing frequency of the dead bus relays and if any additional corrective actions are warranted.
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