ML19254D782

Discusses Review of Acceptability of Station Electric Distribution Sys.Worst Case Combination of Steady State & Transient Loading Will Not Cause Spurious Operation of Undervoltage Protection or Extend Acceleration Times

ML19254D782
Person / Time
Site:	Prairie Island
Issue date:	10/26/1979
From:	Mayer L NORTHERN STATES POWER CO.
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 7910300142
Download: ML19254D782 (2)

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• MSP NORTHERN STATES POWER COMPANY MIN N E A PO Lis. MIN N E SOTA 5 5409 October 26,19 /9 Director of Nuclear Reactor Regulation U S Nuclear Regulatory Commission Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Adequacy oJ Station Electric Distribution Systems Voltages In a letter dated August 8, 1979 from William Gammill, Acting Assistant Director for Operating Reactors Projects, Division of Operating Reactors, USNRC, we were requested to review the acceptability of the station electric distribution systems with regard to both (1) potential overloading due to transfers of loads, and (2) potential starting transient problems. The recent event at the Arkansas Nuclear One site prompted this request.

In our letter dated September 20, 1976 we submitted the results of an analysis of safeguards bus voltages under worst case conditions. This analysis indicated that under maximum transformer load with the minimum expected grid voltage the essential 4 kV bus voltage would be no lower than 3.82 kV. The setpoint for the undervoltage protection devices installed as required by the NRC's June 3, 1977 letter was chosen to be >88% (3.66 kV).

This setting provides the minimum acceptable voltage on the safeguards busses.

A preliminary analysis of motor starting capability under transient conditions was provided to the NRC in our letter dated September 12, 1979. This was an analysis of the worst case 480V bus. We believe there will be no difficulty in starting safety related notors under all conditions of expected grid voltage and bus loading. A detailed analysis of transformer loading and bus voltage under all potential grid and loading conditions is now in progress.

Based on the above considerations ve believe the worst case combination of steady-state and transient loading at Prairie Island will not cause spurious operation of the undervoltage protection or unacceptably extend acceleration times for our emergency loads.

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October 26, 1979 Page In addition, our review to date indicates there is no potential for violation of GDC-17 of Appendix A to 10 CFR Part 50, due to system deficiencies. A review of the potential for transformer overloading and the detailed voltage analysis required by Mr Gammill's August 8,1979 letter have not been completed, however. These analyses, with tests to verify the results, cannot be completed in less than six months. We are proceeding with this work and will forward the results to the Commission Staff when they are available.

Please contact us if you have any questions related to the information we have provided or our schedule for completing the analyses requested in Mr Gammill's August 8, 1979 letter.

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L 0 Mayer, PE Manager of Nuclear Support Se rvices LOM/DKM/jh cc J G Keppler ,. , , ,

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