ML20127G466
| ML20127G466 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 04/24/1973 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9211160611 | |
| Download: ML20127G466 (1) | |
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yvL NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401 I.N/
April 24, 1973 s-X S-
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ih Mr. J. F. O' Leary, Director
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Directorate of Licensing
'n United States Atomic Energy Commission
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Dear Mr. O' Leary:
FDNTICELLO NUCLEAR GENERATING PIXf Ibcket No. 50-263 License No. DPR-22 Improper Closure of No.12 Diesel Generator Breaker A condition occurred at the hbaticello Nuclear Generating Plant which we are reporting to your office in accordance with Section 6.6.C of the Technical Specifications, of Provisional Operating License DPR-22.
On hbrch 30, 1973, during station switching operations an automatic start of both emergency diesel generators was properly initiated when the No. 15 emergency bus nomal supply breaker was opened. However, the No. 12 diesel generator breaker then closed automatically to the No. 16 emergency bus while the bus was energized from the nomal station auxiliary source. Closure of the diesel generator breaker should have been prevented while the bus was energized.
Investigation revealed that the No.12 diesel generator breaker closing pemissive relay was being held in the picked up condition due to interference between the relay nameplate and cover. This pemitted closure of the breaker as soon as the diesel generator reached nomal speed and voltage following an automatic start.
Four relays of this type (General Electric Model 12HGA14BD7) are installed in the
'Ihe name? ates on these relays were found to be 2 inches wide as compared l
plant.
to 1 3/4" for ot1er model HGA relays which have the same size covers. We are awaiting M ormation as to whether the larger nameplate is in accordance with design.
The nameplates for the four relays are being modified to eliminate interference with the cover and window type covers are being installed to pemit visual verifi-cation of proper relay condition.
,q Yours very truly, Q
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L 0 bbyer, PE Director of Nuclear Support Servi -
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"q y cc: B H Grier G Charnoff Minnesota Pollution Control Agency, ATrN:
K. Dzugan