Research Papers

Forensic Examination and Failure Analysis of a 220-MVA Step-Up Transformer Fire

[+] Author and Article Information
Zuhair Ibrahim, Jeremiah Stepan, Ali Reza, Daren Slee

Exponent, Failure Analysis Associates,
5401 McConnell Avenue, Los Angeles, CA 90066

Manuscript received February 18, 2015; final manuscript received April 8, 2016; published online August 19, 2016. Assoc. Editor: Chimba Mkandawire.

ASME J. Risk Uncertainty Part B 2(4), 041003 (Aug 19, 2016) (6 pages) Paper No: RISK-15-1016; doi: 10.1115/1.4033405 History: Received February 18, 2015; Accepted April 08, 2016

The paper presents the results of investigation and engineering analysis by Exponent of the failure of a 220-MVA generator step-up transformer in Southern California. The incident was caused by a dielectric breakdown from the high-side C-phase bushing to the side wall of the transformer. The ensuing fire continued for 27 hrs, fueled by approximately 11,000 gal of dielectric HYTRANS 61 oil. The paper will discuss the investigation conducted as per the IEEE C57.125 “Guide for Failure Investigation, Documentation, and Analysis for Power Transformers and Shunt Reactors,” [1] and the engineering review and analysis to identify the likely failure scenario(s).

Copyright © 2016 by ASME
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C57.125-1991, 1991, IEEE Guide for Failure Investigation, Documentation, and Analysis for Power Transformers and Shunt Reactors.
IEC 60599, 1999, Mineral Oil-Impregnated Electrical Equipment in Service: Guide to the Interpretation of Dissolved and Free Gases Analysis.
NFPA 921, 2008, Guide for Fire and Explosion Investigations.
EPRI, 1995, “Power Transformer Tank Rupture: Risk Assessment and Mitigation,” , Electric Power Research Institute.


Grahic Jump Location
Fig. 1

GSU1 on December 22, 2010, 12:10 p.m.

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Fig. 2

Event data: SEL 351 December 22, 2010, 12:08:22.087

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Fig. 3

IEC 60599 DGA interpretation

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Fig 4

Tank-rupture sequence

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Fig. 5

Initial inspection on January 4, 2011

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Fig. 6

Teardown (east wall)

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Fig. 7

Arc marks at the lower support flange of the high-side C-phase bushing, and on the east-side wall (solid model showing locations of the marks)

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Fig. 8

Copper winding (A, B, and C phases)

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Fig. 9

Dimensional analysis (marked area in the base of the bushing indicates arcing locations, C phase bushing east wall)

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Fig. 10

Rain fall in 2010 near the station

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Fig. 11

Seismic records near San Marcos, CA




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