The transformer bushing is the main insulation device outside the transformer box. The lead wire of the transformer winding must pass through the insulating bushing to insulate between the lead wires and the lead wires and the transformer casing, and at the same time fix the lead wires. Due to different voltage levels, the insulating sleeve has the form of pure porcelain sleeve, oil-filled sleeve and capacitor sleeve. Pure porcelain bushings are mostly used for transformers of 10kV and below. They are made of a conductive copper rod in the porcelain casing, and the air is insulated in the porcelain sleeve. The oil-filled casing is mostly used in the 35kV transformer, which is oil-filled in the porcelain casing. , a conductive copper rod is inserted in the porcelain sleeve, and the copper rod is used to wrap the insulating paper; the capacitor sleeve is used for the high voltage transformer above 100 kV, the main insulating capacitor core, the outer insulating upper and lower porcelain pieces, the connecting sleeve, the oil pillow , spring assembly, base, pressure ball, measuring terminal, terminal block, rubber washer, insulating oil and so on.