The transformer sleeve is the main insulating device outside the transformer box. The lead wire of the transformer winding must pass through the insulating sleeve to insulate the lead wire between the lead wire and the lead wire between the transformer shell, and to fix the lead wire at the same time.Due to different voltage levels, the insulation sleeve has pure porcelain sleeves, oil-filled sleeves and capacitive sleeves.Pure porcelain bushing is mostly used for transformers of 10kV and below. It is to wear a conductive copper rod in the porcelain bushing, and the inside of the porcelain bushing is air insulated.The oil-filled bushing is mainly used in the 35kV class transformer. It is oil-filled in the porcelain bushing. A conductive copper pole is worn in the porcelain bushing.Capacitive bushing is composed of main insulating capacitor core, outer insulating upper and lower porcelain parts, connecting sleeve, oil pillow, spring assembly, base, equalizing ball, measuring terminal, wiring terminal, rubber washer, insulating oil, etc.It is used in high voltage transformers above 100kV.