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Power Transformer: Dry Type & Oil Filled Transformer

Power transformer, a kind of device, utilizes the principle of electromagnetic induction to change alternating voltage. It is mainly composed of coil and iron core (magnetic core). And the coil has two or more than two windings: primary coil and secondary coil. Primary coil is connected with the power source, and the rest is called the secondary coil. And the main functions of power transformer are voltage transformation, current transformation, impedance transformation, isolation, voltage regulation, etc. According to the cooling method, power transformer can be divided into dry type transformer and oil immersed transformer.

An oil-immersed power transformer is on the ground.
Oil-immersed power transformer.A dry type power transformer is on the ground.
Dry type power transformer.
Comparison between dry type transformer and oil immersed transformer

Differences in processing technology 
Dry type transformer depends on the nature air cooling or fan for cooling, while oil immersed transformer relies on the insulation oil as the cooling medium. The iron core and winding of dry type transformer are commonly casted by epoxy resin while the iron core and winding of oil immersed transformer are immersed in the tank filled with transformer oil.
Differences in capacity and voltage 
Dry type transformer is commonly used for distribution with capacity less than 1600 kVA and voltage less than 10 kV. While oil immersed transformer can be used for all capacity and voltage. Dry type transformer should work in rated capacity, while oil immersed transformer has better overloading capacity.
Differences in applicable places 
Dry type transformers mostly are applied for places where need fireproof and explosion-proof, such as the large buildings and high-rise buildings. Oil immersed transformer, after the accident, may have oil spray or oil leakage which would result fire. Thus, oil immersed transformers are usually used in separate rooms or outdoors with accident oil tank.
Differences in cost 
When making power transformer with the same capacity and voltage, the process of making dry type transformer is relatively complex than oil immersed transformer, thus, the cost is also relatively high.