(1) The density should be as small as possible to facilitate the precipitation of moisture and impurities in the oil.
(2) The viscosity should be moderate, too large will affect convective heat dissipation, and too small will reduce the flash point.
(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.
(5) The lower the content of impurities such as acid, alkali, sulfur, and ash, the better, so as to avoid their corrosion to insulating materials, wires, fuel tanks, etc. as much as possible.
(6) The degree of oxidation should not be too high. The degree of oxidation is usually expressed in acid value, which refers to the amount of potassium hydroxide (mg) required to absorb the free acid in 1 gram of oil.
(7) The stability should not be too low. The stability is usually expressed by the sediment of the acid value test, which represents the anti-aging ability of the oil.