TXX-6669, Final Deficiency Rept CP-87-20 Re Cracked Porcelain Connectors on 6.9 Kv Transformers.Initially Reported on 870617.Nonconformance Rept 86-0142 Documents Problem & Subsequent Correspondence W/Transformer Vendor,Westinghouse

Final Deficiency Rept CP-87-20 Re Cracked Porcelain Connectors on 6.9 Kv Transformers.Initially Reported on 870617.Nonconformance Rept 86-0142 Documents Problem & Subsequent Correspondence W/Transformer Vendor,Westinghouse

ML20238B646
Person / Time
Site:	Comanche Peak
Issue date:	08/27/1987
From:	Counsil W, Woodlan D TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
CP-87-20, TXX-6669, NUDOCS 8709010326
Download: ML20238B646 (3)

Text

. _ - _ - _ _

., . :s

- er.i ll ll:' '::ll:~ Log # TXX-6669 L ~ File # 10110 E E 908.3 1UELECTRIC WWiam G. Counsil t w mne n e er" *

• August 27, 1987 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, D.C. 20555 -

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)

DOCKET NOS. 50-445 AND 50-446 CRACKED PROCELAIN CONNECTORS ON 6.9KV TRANSFORMERS SDAR: CP-87-20 (FINAL REPORT)

Gentlemen:

On June 17, 1987, we verbally notified your Mr. H. S. Phillips of a deficiency involving cracked procelain connectors on 6.9KV transformers. An interim report was logged TXX-6576, dated July 17, 1987. We have concluded that this deficiency is reportable under the provisions of 10CFR50.55(e) and the required information follows.

DESCRIPTION OF PROBLEM During inspection of 6.9KV transformers, cracking was identified in the precelain bus connectors. Procelain bus support insulators in transformer cpl-EPTRET-01 were discovered to have loose bolts on Phases B and C, and  ;

damaged procelain on the Phase A insulator. Honconformance Report 86-0142 '

documents the problem and subsequent correspondence with the transformer vendor, Westinghouse.

The transformer vendor, Westinghouse Electric Corporation, recommends a maximum torque value of 20 foot pounds + 1 foot pound be used because ,

overtorquing of the bolts could possibly cause insulator damage. However, during a field modification of the transformer (CP1-EPTRET-01) conducted in March, 1980, instructions were provided to retorque the insulator bolts to 40 foot pounds. The excessive torque resulted in the cracked insulator and the l loose bolts (determined to be caused by stripped threads from overtorquing).

This deficiency is a significant deviation from performance specifications which requires extensive evaluation and repair to assure that the system and l components will perform their intended safety function l 8709010326 870827 PDR ADOCK 05000445 g S PDR O

400 Nonh Olive Street LB 81 Dallas. Texas 75201 g

TXX-6669 August 27, 1987 Page 2 SAFETY IMPLICATIONS Using a conservative approach considering the worst case scenario, cracks in the procelain bus support insulators and loose mounting bolts could, over the life of the transformer, result in short circuits rendering the transformer and connected 480V Class 1E switchgear inoperative. Failure of the bus support insulators during a seismic event, or an electrical short circuit caused by the damaged insulator could prevent the transformer from supplying the Class 1E 480V switchgear loads. Therefore, this condition, were it to have remained uncorrected, could have adversely affected the safety of plant operations.

CORRECTIVE ACTIONS Investigations into the issue of excessive torque has resulted in the identification of four construction travelers which specified the erroneous torque value (40 ft. lbs.). These travelers did not reference the vendor instruction manual and were prepared by the same individual who was incidentally employed at the CPSES project for only a brief period in 1980. A review of all travelers issued during this period (a total of 210 of which 17 were prepared by the specific individual) was conducted which resulted in the identification of no additional instances of excessive torque requests. We have concluded the issue is not a generic concern. However, as a preventative measure, Specification 2323-ES-100, " Electrical Erection Specification", has been revised to clarify bolt torque requirements for both ferrous and non-ferrous applications.

We have determined from a 100 percent reinspection of all 6.9KV transformers that the associated insulators for Unit 1 were overtorqued, Unit 2 were torqued correctly, and torque values for insulators common to both units could ent be determined. Therefore, the Unit 1 and common insulators have been replaced, for all three trains of 6.9KV transformers, and torqued to 20 ft.

Ibs. f 1 ft. lbs.

This completes our corrective action and we anticipate no further reports on this item.

Very truly yours, O.b.Oo<mA.N-W. G. Counsil  !

By:  %

0. R. Woodlan Supervisor, Docket Licensing WJH/grr g3J Zih -l

~ V 6 (10

, ' '3 in c - Mr. R. D. Martin, Region IV Resident Inspectors, CPSES (3)