There are many types of transformer bushings. To maintain the insulation distance between the live part and the ground, bushings are needed in transformers, resistors, circuit breakers, capacitors, and measurement and protection devices in power plants and substations. 

Transformer bushings are the main insulation devices outside the transformer tank. The leads of the transformer windings need to pass through the insulation bushings, which provide insulation to the leads and between the leads and the transformer casing, while also fixing the leads in place. Depending on the voltage level, bushings can be pure porcelain bushings, oil-filled bushings, or capacitor bushings. Transformers of 10kV and below mostly use pure porcelain bushings. Inside the porcelain bushing is a conductive copper rod, and the air inside provides insulation. For 35kV transformers, oil-filled bushings are commonly used. Oil is filled inside the porcelain bushing, which contains a conductive copper rod wrapped in insulation paper. Capacitor bushings are used for high-voltage transformers above 100kV. They consist of a main insulation capacitor core, upper and lower porcelain insulation pieces, connecting bushings, oil reservoir, spring assembly, base, equalizing spheres, measurement terminals, connection terminals, rubber gasket, insulation oil, etc.

Transformer bushing

Generally, bushings are divided into an oil part (inside the transformer) and an air part (outside the transformer). Depending on the insulation type, there are pure porcelain bushings, oil-paper capacitor bushings, epoxy bushings, and silicone rubber bushings. Depending on usage, there are oil-air bushings and oil-oil bushings. There are also other types like dry bushings, rod-through bushings, and conductor rod bushings. Pure porcelain bushings are mainly used for distribution transformers, oil-paper bushings are used for secondary and above transformers. Dry bushings use insulation materials like tape insulation, pure resin insulation, resin-glass fiber insulation, and resin/glass fiber insulation.