Transformers with expansion tanks have the same core and coil structure as hermetic transformers. The dimensions of the expansion tanks of this type of transformers are designed and manufactured as a result of calculations to store the expansion of the oil whose volume increases with temperature. Since the transformers with expansion tanks are open to the atmosphere, the oil pressure changing due to thermal effects is reduced by the air pressure of the air thanks to the clikajel (air dryer) in the transformer's tank.

According to the cooling method, it differs from oil type transformers. HV windings are transformers coated with epoxy cast resin under vacuum. LV windings are transformers that can be manufactured with both cast resin and resin impregnated prepreg method. 25-25000 kVA power range, up to 36 kV voltage level, natural air cooled (AN) or fan cooled

25 - 5000 kVA power range, up to 36 kV high voltage level, three or single phase, oil lubricated, natural cooling (ONAN), with idle tap changer or automatic tap changer under load, can be used both externally and internally. Hermetic oil type distribution transformers, oil pressure and oil pressure by filling oil under vacuum.