Purpose of Electrical Bushings
Types of Bushings
- According to insulating media on ends
- According to construction
- According to insulation inside bushing
- solid type or bulk type
- capacitance-graded or condenser type.
- Air-Insulated Bushings,
- Oil-Insulated or Oil-Filled Bushings,
- Oil-Impregnated Paper-Insulated Bushings,
- Resin-Bonded or -Impregnated Paper-Insulated Bushings,
- Cast-Insulation Bushings,
- Gas-Insulated Bushings.
According to Insulating Media on Ends
- Air-to-oil bushing
- Air-to-air bushing
- Air-to-SF6 bushings
- SF6-to-oil bushings
- Oil-to-oil bushings
An air-to-oil bushing has air insulation at one end of the bushing and oil insulation at the other. Since oil is more than twice as strong dielectrically as air at atmospheric pressure, the oil end is approximately half as long (or less) than the air end.
This type of bushing is commonly used between atmospheric air and any oil-filled apparatus.
- air-to-SF6 bushings, usually used in SF6-insulated circuit breakers;
- SF6-to-oil bushings, used as transitions between SF6 bus ducts and oil-filled apparatus;
- and oil-to-oil bushings, used between oil bus ducts and oil-filled apparatus.
According to Construction
- Solid type (Bulk type) Bushings
- Capacitance-graded (Condenser type) Bushings
Solid Type Bushings
Applications and Limitations of Solid Type Bushings
Capacitance Graded Bushings
This construction uses conducting layers at predetermined radial intervals within oil-impregnated paper or some other insulation material that is located in the space between the central conductor and the insulator.