Dry type transformer: it relies on air convection for cooling, and is generally used for small capacity transformers such as local lighting and electronic circuits. In power system, generally, steam turbine transformer, boiler transformer, ash removal transformer, dust removal transformer and desulfurization transformer are all dry type transformers, with a ratio of 6000V / 400V, and it is used for loads with rated voltage of 380V.

Oil immersed transformer: it depends on oil as cooling medium, such as oil immersed self cooling, oil immersed air cooling, oil immersed water cooling and forced oil circulation. Generally, the main transformer of booster station is oil immersed, with the ratio of 20kV / 500kV, or 20kV / 220kV. Generally, the auxiliary transformer with its own load (such as coal mill, induced draft fan, forced draft fan, circulating water pump, etc.) is also oil immersed transformer, with the ratio of 20kV / 6kV.