ML18289A455

Abb, Inc., 10 CFR Part 21 Notification of Deviation, Dry Type Transformer Serial#: 24-26458

ML18289A455
Person / Time
Site:	Clinton
Issue date:	10/10/2018
From:	Chandler J ABB
To:	Document Control Desk, Office of Nuclear Material Safety and Safeguards
References
24-26458
Download: ML18289A455 (2)

Text

2766884588 09:38:34 a.m. 10-12-2018 1 /2 I

October 10, 2018 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 FAX 301-816-5151 Subject l OCFR Part 21 Notification of Deviation. Dry Type Transfonner Serial#: 24-26458 a

1. This Jetter provides notification of a defect associated with dry type transfom1er serial # 24-26458. The failure was caused by the breakdown of layer to layer insulation within the 4 l 60 Volt winding due to diele~tric stress. Deterioration of the insulation resulted in an internal fault within the Bravo phase 4160 Volt winding, triggering a ground fault trip shut down or this equjprnent. This failure was reported by Exelon's 'Clinton Nuclear Station and it is the only known reported occurrence of safety related transformer 1ailure caused by the breakdown of Jayer to layer insulation. Information is provided as specified in JOCFIUI paragraph 2l.21(d) (4).

2. Notifying individual: Joey ChandJer, Plant Manager, ABB ((PGTR) Power Gdds Transformer Division, US), 171 Industry Drive, Bland Va. 24315.

3. Identification of the Subject component: ABB PIN 24-26458 dry type transformer. This transfonner is used for stepping down voltage and was intended for providing power to safety relate-d electrical equipment

4. Nature of the deviation: The Exelon Clinton Nuclear Generating Station shut down due to a ground fault aJann on the 4160 Volt side of the stepdown transfonner that provides power to numerous safety-related components at the plant Subsequent troubleshooting of the problem revealed that the dry-type transformer supplying 480Volt power had dielectrically failed due to apparent internal fault within the Bravo phase. Further investigation of this failure revealed an operational voltage design stress on the Nomex 410 insulation between t.he 4160 volt winding's layers of conductor greater than recommended by the manufacturer (Dupont) for a 40 year design life. At the time of failure, the subject transformer had been in operation for

• approximately 33.5 years and had progressed 37 years and two months into ils intended 40 year life given the 10/1980 ship date. ABB has no knowledge of any adverse operationtil

• variances over the course of the approximate 33 .5 year life of operation to be ab.le to assess or comment on this potential impact in terms of life.

5. The function of this dry type transformer is to step voltage down from 4160 volts Lo 480 volts while providing transfer o.f power to safety related component'>. Exelon's' Clinton Nuclear Power Station has identified this transformer's power tra11sfer to feed safety related equipment_ An interruption of this transfer in power would result in a loss of power to the satety related equipment downstream and could potentially 1:esult in a compromise in safety.

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6. ABB was notified of this transformer failure 12/9/2017. This notification was delayed while the failure was being investigated. This investigation is documented in report: Exelon Clinton Failure Analysis_26458_011218 rev5.doc.pdf dated 09/10/2018.

7. Corrective actions include:

a. Reviewed and verified current electrical engineering safety related design standard for allowable design stress 011 insulation per Dupont's recommendation for 40 year life.

(Complete.) * *

b. Reviewed the material used for transformer 24-26458. Found only affected safety related product to be isolated to Clinton Nuclear Station, though records may be incomplete as these records have been archived for over 35 years. (Complete.)

c. Re~trained .all involved personnel of the 10CFR21 reporting re-quiremcnts, and ihe need to provide an interim report within 60 days of discovery. *

d. ABB worked directly with Clinton Nuclear to ensure all transformers of respective design was replaced with new transformers following ABB's Technical Evaluation for Nuclear lE Transfonner, Rev. 18 which documents operational design stresses be less than or equal to 30 volts / mil of Nomex 410 insulation between layer to layer of conductor for 40 year life.

8. Recommendation: Because of the possible existence of additional a.fleeted transformers, ABB (PGTR) cannot detennine if the potential for a substantial safety hazard exists at any other licensee's facility. Licensees are requested to evaluate any Gould-Brown Boveri/ITE dry type transformer with the foIJowing nameplate identification below. Tmnsformers associated with this identification are recommended to be replaced.

kVA: 750 AA/ 1000 FA I-N: 4160 Delta Connected LV: 480 Wye Connected Class: AA I FA Type: Vent Frequency; 60 HZ Temp Rise: 80"C Date of Manufacture: 10/1988 and older models Questions concerning this notification should be directed to' the Quality Manager (Rick Kinder) at th*c ABB transformer plant in Bland Virginia at (276) 688- 3325.

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Chandler Manager Power Grids Transformer Division, US ABB inc..

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