The transformer oil is a mineral oil which get from natural petroleum by distilling and refining. The lubricating oil fraction in petroleum is treated by acid-base refining to obtain a mixture of liquid natural hydrocarbons which are pure and stable with small viscosity, good insulation and good cooling property. The selection of transformer oil is generally based on the altitude of the location where the transformer is installed. The commonly used one is 10#20#45#. The higher the altitude, the higher the oil number.
It has following functions.
1, The transformer oil has high dielectric strength than the air. The insulation materials is soaked in oil. It not only improve the dielectric strength, but also avoid the tidal air erosion.
2, The transformer has high specific heat which is usually as coolant. The heat produced by transformer to make the oil of iron core and windings expansion. The oil convection make the heat out of the transformer to ensure the normal operation.
3, On load tap changer of transformer and oil circuit breaker, the contact changing would create arc. Due to good conducting property and under the high temperature of arc to make amount of gas and large pressure which improve The arc-extinguishing performance of the medium makes the arc quench quickly.