Air Insulated Switchgear
An electric power substation that has the bus bars and equipment terminations generally
open to air and utilizes insulation properties of ambient air for insulation to ground.
Gas Insulated Switchgear
An electric power substation in which all live equipment and bus bars are housed in grounded metal enclosures sealed and filled with sulfur hexafluoride gas. An effective although more costly form of switchgear is "gas insulated switchgear" (GIS), conductors and contacts are insulated by pressurized (SF6) sulfur hexafluoride gas. Advantage of GIS comparing to conventional air insulated substation are space saving, high reliability and easy maintenance.