Similar Cases:

Glass Furnace Failure and Transformer PCB Release

Transformer Fire in an Electric Power Plant in Los Angeles

Transformer Explosion at a Hydroelectric Station

An explosion and following fire occurred inside the main step-up transformer at a hydroelectric station in California. In addition to destroying the transformer, the incident shut down the generator and damaged an adjacent gas unit circuit breaker, bus ducts and auxiliary equipment. Fire fighting was unsuccessful, so the fire was allowed to burn itself out. Due to the large volume of cooling oil in the transformer, the fire lasted 48 hours.
The transformer was rated at 158 MVA, three-phase, with forced oil and air (FOA) cooling. The tranformer was not repairable and had to be replaced. APTECH was asked by the insurance adjuster to investigate the cause of the fire. We visited the site to inspect the transformer, review maintenance logs and interview witnesses and plant personnel. Based on the physical evidence, an oil analysis, interviews, the weather and the operator's logs, we proposed and evaluated several potential causation theories. We ruled out lightning, sabotage and a winding or insulation fault. We found that the most likely cause of the incident was the catastrophic failure of the bushing on the B Phase of the three high voltage phases. Failure of the bushing created an arc between the B Phase conductor and the transformer case. This generated gases and pressure, which were explosively released from the transformer. Smaller explosions occurred after the other two phases began arcing.
Due to the extensive damage to the transformer, the root cause could not be determined definitively. However, maintenance and repair records showed that the bushings on the other two phases were repaired several years earlier, but, for some reason, the Phase B bushing was not. This bushing probably had reached the end of its useful life and should have been inspected and repaired.

Satish Almaula		Plant failure and root cause analysis; process and design engineering analysis; process technology development and testing; plant engineering, operations, maintenance and safety management; plant and process control system management.

Kimble Clark, Ph.D.		Failure analysis, heat transfer & thermodynamics, process plant equipment failures & explosions, fuel science, combustion, industrial fires and explosions.

Richard Schreiber, P.E.		Machinery and mechanical device failure analysis, mechanical testing, combustion and heat transfer, industrial fires and explosions, gas appliances.

Eric Sullivan, P.E.		Metallurgy, welding, failure analysis, fire and explosion investigations, equipment, piping.

Michael Cronin, P.E.		Stress analysis, design evaluation, engineering mechanics