Oil-immersed distribution transformers are transformers that change input and output voltages at desired rates up to 36 kV voltage level and 5000 kVa power, and in which the heat generated during operation is dissipated with the transformer oil and cooling is provided by the transformer oil so that it does not exceed the permitted operating temperature. These types of transformers can be examined under 2 (two) main headings as hermetic and expansion tank:
Hermetic Oil Type Distribution Transformers
They are manufactured in the power range of 25 - 5000 kVA, up to 36 kV high voltage level, three or single phase, oil, natural cooling (ONAN), idle tap changer or automatic tap changer under load, and can be used both outside and inside. Hermetic oil type distribution transformers are manufactured with the principle of balancing the oil pressure and atmospheric pressure at the desired temperature by filling the oil under vacuum and preventing the cooling oil from coming into contact with the atmosphere. In hermetic oil type distribution transformers, the internal heat resulting from the changing oil pressure due to thermal changes is controlled by the natural expansion and contraction of the tank wave walls. The mechanical design and manufacturing are made to withstand these effects. Hermetic oil type distribution transformers are lower in height compared to transformers with expansion tanks. Therefore, they can be used in smaller areas. Since the oil in hermetic transformers does not come into contact with the atmosphere, they do not require oil changes at certain periods as in transformers with expansion tanks.
