IR 05000498/1989026
| ML20246E978 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 08/25/1989 |
| From: | Gagliardo J, Kelley D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20246E976 | List: |
| References | |
| 50-498-89-26, 50-499-89-26, NUDOCS 8908300093 | |
| Download: ML20246E978 (4) | |
Text
{{#Wiki_filter:- - - N . *, , , , . . APPENDIX U.S. hDCLEAR REGULATORY COMMISSION
REGION IV
NRC Inspection Report: 50-498/89-26 Operating Licenses: NPF-76 50-499/69-26 NPF-80 Dockets: 50-498 50-499 Licensee: Houston Lighting & Power Company (HL&P) P.O. Box 1700 Houston, Texas 77001 Facility Name: South Texas Project (STP) Inspection At: South Texas Project, Bay City, Texas inspection Concucted: July 18-20, 1989 Inspectort lahd. 8!24 f D. L. Kelley,'Eeactgr Insp ter. Operational phte / - Programs Section,/Divis n of Reactor Safety Approved: - cw 41A 2[ 8[ . . (Gegl/ardo, ChiH Operational Programs [[ ate & Section tDivision of Reactor Safety Inspectior. Summary Inspection Conducted July 18-20, 1989 (Report 50-498/89-26) Areas inspected: No inspection of STP, Unit I was conducted.
Inspection Conducted July 18-20, 1989 (Report 50-499/89-26) Areas Inspected: Nonroutine, announced special inspection of the failure of SIP, Unit 2 Generator Output Transformer 2A.
Results: The transformer failure of July 13, 1989, appeared to be the result of the failure of the Phase A high voltage bushing. The inspector wcs satisfied with the scope and depth of the licensee's investigation.
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. . . -2-DETKILS 1.
Persons Contacted HL&P
- L. H. Clark, Senior Consulting Engineer A. W. Harrison, Supervising Licensing Engineer A. C. McIntyre, Marager Support Engineering The inspector also contacted other members of the licensee's staff during
{ the inspection.
' Denotes person with whom telephone exit interview was held on July 20, 1989.
2.
Damace to STP Unit 2 Generator Output Transformer 2A On July 13, 1989, the Unit 2 Generator Output Transformer 2A was severely damaged by a Phase A ground fault. The inspector was dispatched to the South Texas Project site on July 16, 1989, to perfcrm a followup inspection of the circumstances and assess the damage that resulted from the fault lockout trip.
2.1 Transformer Description The Unit 2 generator output step-up transformer is made up of two kVA (Lilovoltemperes) parallel.The transformer identical three-phase transformers operated in The specifications and total rating is 1,400,000 . ratings for each transformer are as follows: Manufacturer: McGrow-Edison Pating: 700,000 kVA 9 55 C rise /784,000 p 65 C rise FOA (Forced oil and air) Primary voltage 25 kV (kilovolts) Delta connected Secondary Voltage 362.25 kV Wye connected (nominal voltage 345 LV) i I Primary Bushings: General Electric Type T I Secondary Bushings: McGrew-Edison Type PA , l Transformer Weight: Full dressed with oil - 851,700 lbs.
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i L 2.1.1 Event Description At approximately 8 p.m. on July 13, 1989, Unit 2 Generator Output Transformer 2A experienced a Phase A to ground fault at full load L resulting in generator /recctor trip. The fault resulted in extensive damage to both the external-and internal portions of the transformer.
2.1.2 Damane Description The phase-to-ground fault of the high voltne side of the transformer resulted in an explosion, which opened an ll-foot welded seam l approximately 4 feet from top on the north side of the transformer.
' At its wioest point, the open seam was approximately 1-foot wice.
The force of the explosion damaged the north oil radiator and buckled its support members. A large volume of mineral oil and porcelain pieces was ejected through the split seam.
It also appeared that the concussion broke the Phase B lightning arrester at its base.
Examination of the three high voltage bushings revealed that the lower porcelain of the Phase A bushing was missing. The corona shield was also missing (it was inside the transformer).
Further examination of the Phase A bushing revealed arc strikes on the corona i l shield flenge, the lower edge of the ground sleeve, and the bolting l flange. The craft paper wrapping was torn and appeared to have arc tracks on it. The bushing to transformer connection showed no evidence of arc or mechanical damage.
The inspector did not examine the inside of the transformer tecause of the work in progress in preparation for moving the transformer.
The inspector did, however, examine photographs and video tapes made by the licensee. The major portien of the damage inside the transformer appeared to have been caused by the shock wave of the explosion. The tap changers were all broken from their operating mechanism and some of the insulation was out of place. The Phase A bushirg corona shield had slipped down around the connection pigtail.
The connection mating surface cf the Phase A pigtail showed no arc or mechanical damage. There was, however, arc strike evidence at the Phase A bushing penetration at the top of the transformer. There was also some porcelain from the bushing in the transformer windings, A review of the transformer's history revealed that after receipt at i STP, the transformer was loaned out to another HL&P power station in May 1985. The transformer was returned to STP in June 1986, but was again returned to the same power station that same month. The transformer was returned to STP in October 1987, and installea in place on Unit 2.
The inspector also reviewed the electrical and oil test records for Transformer 2A. These tests were performed after the return and installation on Unit 2.
All the test results appeared tv be within specifications.
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+,,. ;. ^ *.;, . t ' ,4 . l.[ ' -4.. ., , , ' 2.1.31 Conclusions- , 'From the observations. 'it would appear that the lower portion 'of the ' Phase A bushing failed and the subsequent arc over to ground caused an internal explosion, which ceused the major portion of.the visible ' damage.
2.1.4 Exit The inspector held a telephone exit interview with Mr. L. H. Clerk' on.
July.?O. 1989, to discuss the results of the inspection. The licensee- < .did not identify any proprietary information to the inspector.
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