ML19338E617
| ML19338E617 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 09/26/1980 |
| From: | Parker W DUKE POWER CO. |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, SD-369-80-16, SD-370-80-11, NUDOCS 8010030459 | |
| Download: ML19338E617 (3) | |
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i DUKE Powen COMPANY Powen Burtoir.-
422 Sourn Cisuucts Srazer, C :Aug. orts, N. C. asa4a w.m o.
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September 26, 1980 ACE PetteOrgt 7tatPeeO*.g. Aega 704 S f tene Phoowctiog 373 4C83 Mr. James P. O'Reilly, Director U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 Re: McGuire Nuclear Station Units 1 and 2 Docket No. 50-369 and 50-370
Dear Mr. O'Reilly:
Pursuant to 10CFR 50.55e please find attached Significant Deficiency Report SD 369/80-16, 370/80-11.
V ry'truly yours,
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/.Ah b w..._ d William O. Parker, Jr. CI 1.JB: ses Attachment cc: Director Mr. Tom Donat, NRC Inspector Office of-Inspection & Enforcement McGuire Nuclear Station U. S. Nuclear Regulatory pommission Washington, D. C.
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a DUKE POWER COMPANY MCGUIRE NUCLEAR STATION Repo,rt Number: SD 369/8C-16, 370/80-11 Report Date: September 26, 1980 Facilities: McGuire Nuclear Station, Units 1 and 2 Identification of 'eficiency:
Potential Transformers / Cables D
Connected to Diesel Generators Overvoltage During Ground Faults Description of Deficiency:
On August 28, 1980, J. R. Wells and W. J. Foley reported by telephone the follow-ing deficiency to Mr. John Rausch of the NRC, Atlanta.
the 4.16KV Essential Power System at McGuire is designed to operate continuously with a single phase-to-ground fault on the system when being powered by the diesel generator (DG). Since the DG is high resistance grounded, the voltage with respect to ground on the two unfaulted phases could rirL to line-to-line valucs should a phase-to-ground fault occur. This system utilizes phase-to-ground and Y-Y connected PT's with the neutral on the primary solidly grounded. Since the PT's are solidly grounded, the phase-to-ground PT's connected to the two unfaulted phases could then have up to line-to-line voltage impressed across them. However, the PT's and some equipment in the secondary circuits are not rated for phase-to-phase voltage.
At McGuire, SKV phase-to-phase rated cables are used between the generator and the regulator. These cables must be rated for 4160 volts phase-to-ground, i.e.
a minimum rating of 7200 volts phase-to-phase. The requirement that these components be rated for continuous operation with 4160 volts phase-to-ground was overlooked in the initial design.
Analysis of Safety Implications:
During continued operation of the DG with a ground fault, the resultant over-voltage on the two unfaulted phases with respect to ground (4160 volts) could cause insulation breakdown on the DG 1ead cables and the 4.16KV system metering and monitoring PT's.
The fuses protecting the PT's would probably isolate the PT's f rom the overvoltage, resulting in loss of voltage indication on the 4.16KV Essential Power System.
It should be noted that once the DG is started automatically via the DG sequencer, there is no manual control capability until the sequencer is reset. The only manual function available in this mode is the emergency stop button.
Insulation breakdown on the DG 1ead cables could cause a differential protective relay trip of the DG.
Corrective Action:
All phase-to-ground and wye connected PT's on the 4.16KV system will be replaced with phase-to-phase and open-delta connected PT's.
As a result of the PT's connection changing from wye to open-delta, several voltage and frequency transducers, voltmeter selector switc;ies, and the DG watthour meters will have to be replaced also. All equipment has been ordered, and this work is expected to be completed by December 1,1980 cns McGuire Unit I and before initial fuel loading on McGuire Unit 2.
The DG lead cables will be replaced with cable having an 8KV insulation rating, therefore giving insulation of 4.62KV line-to-ground on the cables. The replace-ment cables are onsite, and this work is expected to be completed by December 1, 1980 on McGuire Unit 1 and before initial fuel loading on McGuire Unit 2.
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