ML20195H829

Final Deficiency Rept CP-87-93 Re Motor Control Ctr Starter Coils.Initially Reported on 870903.Design Basis Documents Issued to Provide Criteria for Correct Calculation of Circuit Voltage Drops Under Worst Case Operating Conditions

ML20195H829
Person / Time
Site:	Comanche Peak
Issue date:	01/11/1988
From:	Counsil W TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
CP-87-93, TXX-88074, NUDOCS 8801200362
Download: ML20195H829 (2)

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=M P Log # TXX-88074  ;

._ C Fi1e # 10110 r = 908.3 1UELECTRIC

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IO*,hS$,U,,, January 11, 1988 ,

U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION DOCKET NOS. 50-445 AND 50-446

, MCC STARTER C0ILS i

SDAR: CP-87-93 (FINAL REPORT)  ;

Gentlemen:

On September 3,1987, we verbally notified your Mr. H. S. Phillips of a deficiency involving MCC starter coils. Our last interim report was logged l TXX-6788, dated October 5,1987. We are reporting this issue under the i provisions of 10CFR50.55(e). The required information follows.

l DESCRIPTION Calculation 16345-EE(B)-007-XXX-13H determined that eleven MCC starter coils l may not pick-up due to excessive circuit length, should the voltage at the MCC bus fall to the design value of 422V. This condition would occur when the existing station start-up transformers are at worst case loading concurrent with minimum voltage on the 138kV system. This condition is limited to the control circuits for the exhaust fans located in the control room, electrical area on elevation 852 f t. - 6 in, and the battery rooms. This deficiency is due to the failure of the responsible design organization to correctly calculate the worst case MCC voltages.

SAFETY IMPLICATIONS Shou'd the MCC bus voltage fall to the design minimum of 422V, the affected safety circuits and coils may not be capable of energizing the associated  :

safety components.

This condition represents a significant final design deficiency su. that the design does not conform to the criteria stated in the FSAR.

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TXX-88074  :

January 11. 1988 Page 2 of 2 CORRECTIVE ACTION The loading condition on the existing station start-u) transformers was

identified as a reportable issue on SDAR CP-87-91. T11s condition produced overloaded transformers and voltage problems on the electrical system. The corrective action for SDAR CP-87-91 was to add two additional transformers. ,

With the addition of the new start-up transformers,'the voltages at the MCC .

busses will be raised to a minimum of 435V thus correcting the deficiency of '

starter coil pick-up. Therefore, no additional corrective action is required beyond the corrective action that was implemented for and reported under  :

SDAR CP-87-91.

Design Basis Documents have been issued to provide criteria for the correct calculation of circuit voltage drops under worst case operating conditions to prevent the recurrence of this deficiency.  :

Very truly yours, ,

frA&nf

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W. G. Counsil WJH/grr *

, c- Mr. R. D. Hartin, Region IV Resident Inspectors, CPSES (3) l L

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