Transformer bushing: This is an insulating device that brings the transformer winding out to the outside of the oil tank. It acts as insulation between the conductor and the tank, and also serves to secure the conductor.  

During transformer operation, the bushing carries the load current over long periods, and in case of an external short circuit, it carries the short-circuit current.  

Transformer bushings are the main insulation devices outside the transformer tank. The transformer’s output lines must pass through the bushing, which insulates the line and connects the line to the transformer casing while also securing the output line. Depending on the voltage level, bushings can be all-ceramic, oil-filled, or capacitor type. All-ceramic bushings are mainly used for transformers of 10kV and below. A conductive copper rod is inserted into the ceramic sleeve, and the sleeve provides air insulation. Oil-filled bushings are mainly used for 35kV transformers, where the ceramic sleeve is filled with oil, a copper conductor is inserted, and the outside of the sleeve is wrapped with insulating paper. Capacitor bushings are made up of a main insulation capacitor core, external upper and lower ceramic pieces, connecting bushing, oil reservoir, spring assembly, base, grading spheres, measurement terminals, wiring terminals, rubber gaskets, insulating oil, etc., and are used for high-voltage transformers above 100kV.

What does the structure of a transformer bushing look like?  

A bushing mainly consists of the capacitor core, oil reservoir, flange, and upper and lower ceramic sleeves. The main insulation is the capacitor core, made from a series of concentric capacitors. It’s enclosed in a sealed container made up of the upper and lower ceramic sleeves, oil reservoir, flange, and base. The container is filled with treated transformer oil, creating an oil-paper structure inside the main insulation. Contact surfaces between the main housing parts are lined with oil-resistant rubber gaskets. A set of springs in the oil reservoir applies pressure in the middle to fully seal each component. The flange has a vent plug, oil sampling device, and a set for measuring dielectric loss and partial discharge (PD). During operation, the measurement device cover must be in place, the end screen grounded, and opening the circuit is strictly prohibited.  

For connecting the high-voltage lead of the transformer bushing, there are methods like threading the wire through or using a conductor rod to carry the current.