The disadvantage of this type of transformer is that they are large in size because of oil tank & the sensors required for the inspection of humidity etc. It contains flammable oil so they are not suitable for an indoor environment.
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Based On Phase
Single Phase Transformer:
Single phase transformer is a two winding transformer having one primary winding & one secondary winding. The transformer is used for single phase application like Microwave oven, cellphone charger etc.
They have two input terminals connected with primary windings & two output terminals connected with the secondary winding.
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Three Phase Transformer:
Three phase transformers has 6 windings in which 3 of them are primary winding & 3 are secondary windings for each phase. It has 12 terminals evenly divided on both sides (2 for each phase) considering star & delta connection. You can use 3 single phase transformers together instead of a 3-phase transformer.
They are used for power transmission & power distribution for domestics & commercial uses.