(1) Insulation function: transformer oil has much higher insulation strength than air. The insulating material immersed in oil can not only improve the insulating strength, but also prevent the erosion of moisture.
(2) Heat dissipation: the specific heat of transformer oil is large, and it is often used as coolant. The heat generated during the operation of the transformer causes the oil close to the iron core and winding to expand and rise when heated. Through the up and down convection of the oil, the heat is dissipated through the radiator to ensure the normal operation of the transformer.
(3) Arc suppression function: on the on load voltage regulating switch of the oil circuit breaker and transformer, the contact will produce an arc when switching. Due to the good thermal conductivity of transformer oil, and under the action of high temperature of the arc, it can separate a large amount of gas and generate greater pressure, which improves the arc extinguishing performance of the medium and makes the arc extinguish quickly.
The performance of transformer oil is generally required as follows:
(1) The density of transformer oil shall be as small as possible to facilitate the precipitation of water and impurities in the oil.
(2) The viscosity should be moderate. Too low viscosity will affect the convection and heat dissipation, and too low viscosity will reduce the flash point.
(3) The flash point shall be as high as possible and generally not lower than 136 ℃.
(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, so as to avoid their corrosion to insulating materials, wires, oil tanks, etc.
(6) The oxidation degree shall not be too high. The degree of oxidation is usually expressed by acid value, which refers to the amount of potassium hydroxide required to absorb free acid in 1g oil (mg).
(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