1. The viscosity should be moderate. If it is too high, it will affect convective heat dissipation, while if it is too low, it will lower the flash point.

2. The density of transformer oil should be kept as low as possible to facilitate the precipitation of moisture and impurities in the oil.

3. The flash point should be as high as possible, generally not lower than 136 ℃.

4. The freezing point should be as low as possible, and transformer oil is classified according to its freezing point. The lower the freezing point, the more it proves that transformer oil can be used at lower temperatures.

5. The lower the content of impurities such as alkali, sulfur, and ash, the better to avoid their corrosion on insulation materials, wires, oil tanks, etc. as much as possible.

6. High oxidation resistance: Transformer oil gradually oxidizes when exposed to air during use, and also accelerates oxidation when exposed to high temperatures. The oxidized oil gradually ages and becomes ineffective, so the higher the oxidation resistance of transformer oil, the better. Compared to synthetic oil, synthetic oil is more stable and resistant to high temperatures.

7. Low acid value: The acid value must be low to reduce corrosion of conductivity and metals.