The main functions of transformer oil:
(1) Insulation effect: Transformer oil has a much higher insulation strength than air. The insulation is immersed in oil, which not only improves the insulation strength but also protects it from moisture attack.
(2) Heat dissipation: Transformer oil has a large specific heat and is commonly used as an agent. The heat generated when the transformer is running causes the oil close to the iron core and windings to expand and rise. 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-extinguishing effect: On the on-load voltage regulating switch of the oil circuit breaker and the transformer, arc will be generated when the contacts are switched. Since the transformer oil has good thermal conductivity, it can separate a large amount of gas under the high temperature of the arc and generate a large pressure, thus improving the arc extinguishing performance of the medium and extinguishing the arc quickly.
The performance of transformer oil usually has the following requirements:
(1) The density of transformer oil should be as small as possible to facilitate the precipitation of moisture and impurities in the oil.
(2) The viscosity should be moderate. If it is too high, it will affect convection heat dissipation. If it is too small, it will reduce the flash point.
(3) The flash point should be as high as possible, generally not lower than 136°C.
(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 corrosion of insulating materials, wires, fuel tanks, etc.
(6) The degree of oxidation cannot be too high. The degree of oxidation is usually expressed in terms of acid value, which refers to the amount of potassium hydroxide (in milligrams) required to absorb the free acid in 1 gram of oil.
(7) It should not be too low, usually expressed by the sediment of the acid value test, which represents the oil's ability to resist aging.
