What is the working principle of transformer bushing? 

Working principle of transformer bushing 

Basically a bushing consists of several components. But we will take a general look at the main working principle. It mainly consists of an insulated body, into which the conductor passes.

The insulation is usually made of porcelain or capacitance-grade material because it increases the dielectric strength. There is a space between the insulation body and the conductor. This space is filled with electrical-grade mineral oil, which has excellent insulation properties. It prevents direct contact between insulator and conductor.

Porcelain is used because it handles a lot of electrical stress. Basically the same theory goes with capacitance-graded materials. Because high voltage stress can break low quality insulation very easily, it is important to use this type of material. Also, they have excellent mechanical strength, which increases the life of the bushing.

Oil is properly filled in proportion to transformer tank level as well as insulated body level. When current flows through a conductor, due to the presence of such insulation around it, it is confined only within the body of the conductor. The voltage flows directly between the inner windings and the current-carrying outer wires. This avoids contact with the external environment and thus prevents the transformer body from any untoward incident. The bushing controls the size and intensity of the electric field and thus reduces the electric force on the insulating material. Thus the bushings can easily use higher voltages starting from 11KV and can go above 33KV.