How many types are there for the cooling methods of transformers?

The common cooling methods for power transformers are generally divided into three types: oil-immersed self-cooling, oil-immersed air-cooling, and forced oil circulation. The oil-immersed self-cooling type relies on the natural convection of oil to carry heat to the tank walls and heat dissipation tubes, and then uses air convection to dissipate the heat; it does not have any specialized cooling equipment. The oil-immersed air-cooled type builds on the oil-immersed self-cooled type by installing fans on the tank walls or heat dissipation tubes, using the airflow from these fans to assist in cooling. Installing air cooling can increase the capacity of the transformer by 30% to 35%. The forced oil circulation cooling method is further divided into forced oil air cooling and forced oil water cooling. It uses an oil pump to send the oil from the transformer into the oil cooler and then return it to the oil tank. The oil cooler is designed in a special shape that facilitates heat dissipation, using a fan to blow air or circulating water as a cooling medium to carry away the heat. By tripling the oil circulation speed compared to natural convection in this approach, the transformer’s capacity can be increased by 30%