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REUASLE ELECTRICITY FOR MAINE SINCE 127?

|EDISON DRIVE . AUGUSTA. MAINE 04330 . (207) 622 4868

March 31, 1989MN-89-42 GDH-89-118

Director of Nuclear Reactor RegulationUnited States Nuclear Regulatory Comm13sionWashington, D. C. 20555

Attention: Mr. Richard H. Wessman, Project Director I-3Division of Reactor Projects I/II

References: (a) License No. DPR-36 (Docket No. 50-309)

Subject: Maine Yankee Offsite Power

Gentlemen:

The purpose of this letter is to transmit the design report for therecently installed 115 kV Capacitor Bank at Maine Yankee and to clarify ourposition regarding enhancements to the plant's offsite power system.

The enclosed "115 kV Capacitor Bank Design Report" summarizes the designbasis, capabilities and planned periodic testing for the capacitor bank thatwas installed during the 1988 refueling outage to ensure the continuedreliability of the plant's off-site power supply. He have reviewed theinstallation of the capacitor bank and evaluated the results of functionaltesting. As a result, we have concluded that the capacitor bank is fullyoperational.

Central Maine Power (CHP) based the 30.6 MVAR sizing of the capacitor bankon load studies which evaluated the Surowiec line voltage with the worst casedynamic load of 55 MVA at Maine Yankee and the steady state lead of 43.45 MVAat Bath and Topsham substations. The 43.45 MVA assumed the 1988/89 ForcastedHinter Peak Load and Section 207 Mason out of service. CMP also performed afive year base case model (1993/94 Forecasted Hinter Peak Load) whichprojected the Surowiec line load of 42.69 MVA at Bath and Topshamsubstations. The decrease in Suroweic line load is predicated on load beingsupplied by additional hydroelectric generttion planned for this area. Thesestudies by CMP indicate that the capacitor bank will provide adequate voltagesupport of the Surowiec line for at least the next five years.

Although we believe the offsite power system design meets all applicableregulatory requirements, we have previously indicated our intention to makefurther enhancements to the offsite power system in order to resolve concernsexpressed by NRC staff. Maine Yankee is prepared to install a redundanttransformer in parallel to the existing X-14 transformer. This transformer,sized to carry design station loads without the existing X-14 transformer,should improve the reliability of offsite power and assure the adequacy of thevoltage on the 115 kV line even without the capacitor bank.

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United States Nuclear Regulatory Commission Page TwoAttention: Mr. Richard H. Hessman HN-89-42

Maine Yankee is evaluating a second enhancement to the electromechanicalrelays in the auto bus transfer logic. Should our evaluation prove thatreplacement of the electromechanical relays would improve the timely transferof station loads to offsite power in the event of fast clearing electricalfaults similar to the August,1988 main transformer fault, then the relayswill be replaced.

He are proceeding with the design of the redundant transformer andevaluation of improvements to the auto bus transfer system. He would like toimplement the eventual improvements by the end of the spring, 1990 refuelingoutage. However, prior to installing these changes, we request NRCconcurrence that these enhancements will fully resolve NRC's concernsregarding Maine Yankee's offsite power system.

Very truly yours,

MAINE YANKEE

})8 hvG. D. Whittier, ManagerNuclear Engineering and Licensing

GDH:BJP

Enclosure

c: Mr. Hilliam T. RussellMr. Patrick M. SearsMr. Cornelius F. Holden

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