The temperature of transformers tends to increase due to the copper and core losses. The heat should be transferred to the ambient to keep the temperature within safe limits to ensure reliability and extend lifetime of transformers. The most common cooling methods for transformers are as follows.
Air Cooling: This method of cooling is implemented in two ways, natural air cooling and forced air cooling.
- In natural air cooling, the air moves by convection and takes the heat away from the transformer.
- In forced air cooling, fans are used to accelerate the convection process and transfer the heat to the ambient in a more effective way.
Oil Cooling: In this method, the transformer is placed in a tank filled with special oil. Oil also provides insulation between the windings of the transformer and the transformer tank. This method of cooling is implemented in two ways, natural oil cooling and forced oil cooling.
- In natural oil cooling, oil moves within the transformer tank by convection and takes the heat off the transformer.
- In forced oil cooling, fans are used inside the tank to accelerate convection process and thus, cool the transformer in a more effective way.
- In both natural and forced oil cooling, the oil is cooled by fans mounted on the exterior of the tank, which take the heat off the transformer tank and transfer it to the ambient.
Note that the power handling capability of a transformer is reduced because of heating and increased as a result of cooling. In forced cooling, fans turn on based on the measurement of temperature and its comparison with a set point.