Oil immersed transformers use oil as the main insulation method and rely on oil as the cooling medium, such as oil immersed self cooling, oil immersed air cooling, oil immersed water cooling, and forced oil circulation. The main components of a transformer include iron core, winding, oil tank, oil pillow, respirator, explosion-proof tube (pressure relief valve), radiator, insulation sleeve, tap changer, gas relay, thermometer, oil purifier, etc.

Between the layers of silicon steel sheets in oil immersed transformers, due to long-term immersion in the transformer, oil can penetrate into it, and the transformer oil has elasticity and buffering effect, so the noise of oil immersed transformers is low. But its pressure regulating switch is inside the fuel tank, and the contact of the switch during pressure regulation is not visible from the outside. If the contact cannot be made, it is equivalent to a circuit breaker. If the contact is poor, it is easy to burn out the switch when the load is too high.