What Fuel Does the Transformer Use?

Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulation properties. It is used in oil-immersed transformers, certain types of high-voltage capacitors, fluorescent lamp ballasts, and certain types of high-voltage switches and circuit breakers. Its function is to insulate, suppress corona discharge and arc, and act as a coolant.

Transformer oils are usually based on mineral oil, but alternative formulations with better engineering or environmental properties are becoming increasingly popular.

Functions and features

The main function of transformer oil is to insulate and cool the transformer. Therefore, it must have high dielectric strength, thermal conductivity, and chemical stability, and must maintain these characteristics at high temperature for a long time. Typical specifications are: flashpoint 140°C or higher, pour point −40°C or lower, dielectric breakdown voltage 28 kV (RMS), or higher.

In order to improve the cooling of large power transformers, the oil-filled oil tank may have an external radiator, and the oil will circulate naturally through the radiator. Power transformers with a capacity of thousands of kilovolt-amperes may also have cooling fans, oil pumps, and even oil-water heat exchangers.

After a long drying process, the power transformer uses electrical self-heating, vacuum, or both to ensure that the transformer is completely free of water vapor before introducing insulating oil. This helps prevent the formation of corona and subsequent electrical breakdown under load.

Oil-filled transformers with oil conservator (oil reservoir) may have gas detection relays (Buckholtz relays). These safety devices detect gases that have accumulated in the transformer due to corona discharge, overheating, or internal arcing. When the gas accumulates slowly or the pressure rises rapidly, these devices can trip the protective circuit breaker, thereby cutting off the power to the transformer. Transformers without oil conservator is usually equipped with surge relays, whose functions are similar to those of Buchholz relay.

Mineral oil substitute

Mineral oil is still widely used in the industry. Mineral oil is usually effective as transformer oil, but it also has some disadvantages, one of which is its relatively low flashpoint. If the transformer leaks mineral oil, it may cause a fire. Fire codes usually require transformers in buildings to use less flammable liquids or dry transformers that are completely free of liquids. Mineral oil is also an environmental pollutant, and even a small amount of water will rapidly deteriorate its insulating properties. For this reason, transformers are fully equipped to keep water out of oil.

The above information is provided by an oil-immersed transformer manufacturer.