By Mark B. Goff, Cassandra H. Goff

Watch small detail - Avoid big mistakes.

The power industry experience shows that a failure of a high-voltage oil-filled bushing will most likely lead to a catastrophic transformer failure. The fire triangle requires the coexistence of fuel, oxygen and an ignition source. First, the transformer has a large volume of oil as a fuel source. Second, the atmosphere is the source for oxygen. And third, the ignition source which is created by an internal arc from the faulted bushing completes the fire triangle.

As the bushing fails, the pressure wave created by an electrical short circuit inside of a faulted bushing will crack the bushing insulator, thus allowing the bushing oil to atomize. Next, the massive amount of oil from the transformer tank is exposed leading to a catastrophic failure. In extreme cases, the transformer tank will split thus releasing the transformer oil at a higher rate.

If the electrical protection scheme is slow to operate, then the fire suppression system will have a difficult time in extinguishing the fire. 

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This article was originally published in the December 2019 issue of the Critical Failure: Modes & Prevention magazine.

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