Transformer bushing is the main insulating device outside the transformer box. The leading wires of transformer winding must pass through the insulating bushing to insulate the leading wires and the leading wires from the transformer housing, and fix the leading wires at the same time. Due to different voltage classes, the insulated bushing can be pure porcelain bushing, oil-filled bushing and capacitive bushing. The pure porcelain bushing is mainly used for transformers with 10kV and below. It is a conductive copper rod pierced in the porcelain bushing, and the porcelain bushing is air insulated. The oil-filled bushing is mostly used in 35kV transformer. It is oil-filled in porcelain bushing, and a conductive copper rod is threaded into the porcelain bushing. The copper rod is covered with insulating paper. Capacitive bushing is used for high voltage transformers above 100kV. It is composed of main insulating capacitance core, outer insulating upper and lower porcelain parts, connecting sleeve, oil pillow, spring assembly, base, pressure equaling ball, measuring terminal, wiring terminal, rubber washer, insulating oil and so on.
Transformer bushing is leading the internal high and low voltage -wires to external tank case, not only as a lead of insulation, and playing the role of fixing wire, transformer bushing is one of the components for transformer load flow, in transformer operation,transformer bushing need to pass through the overload current for a long time, when outside the transformer short circuit occurs, it also needs to pass through the short circuit current. Therefore, there are the following requirements for transformer bushing:
(1) Must have specified electrical strength and sufficient mechanical strength.
(2) Must have good thermal stability, and can withstand the short circuit of instant overheating.
(3) Small appearance, small quality, good sealing performance, strong versatility and easy maintenance.