Electrical Bushing

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Typical bushing designs (in this case Epoxy Resin Impregnated Paper Bushings, Siemens)

An electrical bushing can be explained as an apparatus for transmitting power in or out of enclosures, i.e., barriers, of an electrical apparatus such as transformers, circuit breakers, shunt reactors and power capacitors. According to the ANSI/IEEE Standard definition an electrical bushing is “an insulating structure, including a through conductor or providing a central passage for such conductor, with provision for mounting a barrier, conducting or otherwise, for the purpose of insulating the conductor from the barrier and of an electrical current from one side of the barrier to the other.”

Since electrical power is the product of voltage and current, the insulation in a bushing must be capable of withstanding the voltage at which it is applied, and its current carrying conductor must be capable of carrying rated current without overheating the adjacent insulation. The bushing must also be able to withstand the various mechanical forces applied to it and in some cases it must also provide sealing (e.g. for transformer oil, SF6 gas).


The bushings may be of the following types:

  • liquid-filled bushing;
  • liquid-insulated bushing;
  • gas-filled bushing;
  • gas-insulated bushing;
  • oil-impregnated paper bushing;
  • resin-bonded paper bushing;
  • resin-impregnated paper bushing;
  • ceramic, glass or analogous inorganic material bushing;
  • cast or moulded resin-insulated bushing;
  • combined insulation bushing;
  • compound-filled bushing;
  • gas-impregnated bushing.