Oil-immersed transformers are called insulating oils. Their role is to prevent breakdown. If the high-voltage end of the transformer is not insulated, it will cause corona or breakdown accidents, causing losses to staff and equipment.

Transformers are not only oil-immersed, nor do they have to be oil-immersed. At present, oil-immersed transformers are mainly used in conventional outdoor, high-voltage, UHV and other fields; dry-type transformers are mainly used in places with higher fire-proof and safety requirements below 110kV; gas-insulated types are mainly used for special field.

Since oil-immersed transformers are insulated by oil, the oil has good insulation properties and is low in price, so it is the most conventional and common insulation structure in the field of transformers.

(1) Insulation: Transformer oil has much higher insulation strength than air. The insulating material is immersed in oil, which not only improves the insulation strength, but also protects it from moisture. This is also the main function of transformer oil.

(2) Heat dissipation effect: The specific heat capacity of transformer oil is relatively large, and it is often used as a coolant. The heat generated during the operation of the transformer causes the oil close to the iron core and windings to expand and rise. Through the upper and lower convection of the oil, the heat is dissipated through the radiator to ensure the normal operation of the transformer.

(3) Arc suppression effect: On the on-load voltage regulating switch of oil circuit breaker and transformer, an arc will be generated when the contacts are switched. Because the transformer oil has good thermal conductivity, and can separate a large amount of gas under the action of the high temperature of the arc, and generate a large pressure, the arc extinguishing performance of the medium is improved, and the arc is quickly extinguished.