(1) transformer oil density as small as possible, in order to facilitate oil moisture and impurities precipitation.
(2) viscosity should be moderate, too much influence convection heat dissipation, too small will reduce flash point.
(3) flash point should be as high as possible, generally should not be lower than 136 degrees centigrade.
(4) the freezing point should be as low as possible.
(5) the lower the content of acid, alkali, sulfur, ash and other impurities, the better to avoid their corrosion on insulating materials, wires, tanks and so on.
(6) the degree of oxidation can not be too high. The degree of oxidation usually expressed in acid value, it refers to the amount of absorption of potassium hydroxide free acid 1 grams oil required (mg).
(7) the degree of stability should not be too low, stability usually test sediment acid value, which represents the ability of anti ageing oil