Dry-type transformer cooling methods are divided into natural air cooling (AN) and forced air cooling (AF). When naturally air-cooled, the dry transformer can operate continuously for a long time at the rated capacity. When forced air cooling, the output capacity of the dry transformer can be increased by 50%. It is suitable for intermittent overload operation, or emergency accident overload operation; due to the large increase in load loss and impedance voltage during overload, it is in a non-economic operation state, so it should not be used for long-term continuous overload operation. This is also why dry type transformers are more popular on the transformer market.