According to the different sources of base oil, transformer oil is mainly divided into four categories: mineral oil transformer oil, vegetable oil transformer oil, silicone oil transformer oil, and synthetic ester transformer oil.

Mineral oil transformer oil has the longest history of application and occupies a dominant position in the market. It is mainly obtained from the processing of cyclohexane based oil and paraffin based oil, with high dielectric strength and volume resistivity, which can effectively ensure the insulation performance of transformers. It has stable performance at high temperatures and good compatibility with various metal materials, making it suitable for large power transformers. However, mineral oil transformer oil also has some shortcomings, such as a relatively low flash point, generally below 140 ℃, which poses a risk of flash ignition in the event of an arc fault in the transformer; And it is non renewable and has poor biodegradability. Once leaked, it can easily cause pollution to the environment.

Plant oil transformer oil has emerged in recent years, which is made from natural oil crops through pressing, refining, and modification. The main component triglycerides give it many advantages, such as high ignition point, which can significantly improve the fire safety of transformers; Good electrical performance, able to meet the operational requirements of transformers; The raw materials are widely sourced and renewable, with excellent biodegradability, in line with current environmental protection concepts. However, vegetable oil transformer oil currently faces some challenges, with prices about 3-4 times higher than mineral oil transformer oil and higher costs; The performance indicators of oil products have not been fully unified, and there are relatively few relevant standards; Its medium loss factor, water content and kinematic viscosity are relatively high, there are also oxidation and gel phenomena, and the operation and maintenance experience is relatively scarce. These factors limit its large-scale promotion to a certain extent.

Silicone oil transformer oil is based on organic silicon liquid and has excellent electrical insulation properties. It has a high ignition point, low pour point, and minimal viscosity change with temperature. Although its viscosity is more than twice that of mineral oil transformer oil, the density difference between cold oil and hot oil is even greater, which can accelerate the thermal siphon convection speed and partially compensate for the lack of heat dissipation. However, silicone oil transformer oil is more sensitive to the decomposition products of partial discharge or breakdown, and has lower stability against electric sparks.

Synthetic ester transformer oil has extremely high oxidation stability, which can maintain stable oil performance for a long time and greatly extend its service life. At the same time, it has good fluidity in low-temperature environments, high flash point, low volatility, and excellent safety.