Type of Cooling Used

There are two categories of transformers in this category: Dry type and oil-filled.

• Dry type transformers use natural air cooling and are commonly of extremely little ratings. They are rugged and easy in construction and are not plagued along with the failures associated with oil cooling.

• Oil filled transformers are of two kinds: One type uses self-cooling and the other type uses forced cooling.

Self-cooling oil filled transformers have natural circulation of insulating oil inside which the whole transformer is immersed. These are of moderate ratings and are appropriate for outdoor duty as these need no housing other than their own and thereby save on cost. For higher ratings, either the smooth surface of tank is corrugated or is provided with radiators/pipes to get greater heat radiation area.

Large transformers required forced oil/water cooling. The coolant is circulated by a pump to radiate high quantity of heat produced and also to minimize the size of the transformer.