The following are the requirements of the performance of transformer oil:
(1) The density of transformer oil must be as low as possible, in this way, it is easy to separate the oil from moisture , impurities.
(2) The viscosity of the transformer oil must be moderate, too high, it is not easy for heat dissipation，too small, it is not easy to low down the flash point.
(3) the flash point should be high, normally, should be no less than 136 ℃
(4)The freezing point should be as low as possible.
(5) The acid, alkali, sulfur, ash content of transformer oil are is lower, is better, in order to avoid corrosion.
(6) The degree of oxidation can't be too high. the acid value is usually to symbolized the Oxidation degree.
(7) The stability degree should not be too low, the impurities which from the testing of acid value to express the stability, it symbolized the ability of antioxidation of transformer oil.