Transformer oil

Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers, some types of high-voltage capacitors, fluorescent lamp ballasts, and some types of high-voltage switches and circuit breakers. Its functions are to insulate, suppress corona and arcing, and to serve as a coolant.

Transformer oil is most often based on mineral oil, but alternative formulations with better engineering and/or environmental properties are growing in popularity.

Transformer oil's primary functions are to insulate and cool a transformer. It must therefore have high dielectric strength, thermal conductivity, and chemical stability, and must keep these properties when held at high temperatures for extended periods. Typical specifications are: flash point 140 °C or greater, pour point −30 °C or lower, dielectric breakdown voltage 28 kV (RMS) or greater. To improve cooling of large power transformers, the oil-filled tank may have external radiators through which the oil circulates by natural convection. Very large or high-power transformers (with capacities of thousands of kVA) may also have cooling fans, oil pumps, and even oil-to-water heat exchangers.

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