DOI link for Electrical Bushings
Electrical Bushings book
As a less formal explanation, the purpose of an electrical bushing is simply to transmit electrical power in or out of enclosures, i.e., barriers, of an electrical apparatus such as transformers, circuit breakers, shunt reactors, and power capacitors. An air-to-oil bushing has air insulation at one end of bushing and oil insulation at the other. An air-to-air bushing has air insulation on both ends and is normally used in building applications where one end is exposed to outdoor atmospheric conditions and the other end is exposed to indoor conditions. Solid bushings are commonly used in applications ranging from small distribution transformers and circuit switchers to large generator step-up transformers and hydrogen-cooled power generators. The space between the lead and the insulator may consist of only air on lower-voltage solid-type bushings, or this space may be filled with electric-grade mineral oil or some other special compound on higher-voltage bushings. The bushing flange creates very convenient site to locate bushing current transformers.