ABSTRACT
A gas-insulated substation (GIS) uses a superior dielectric gas, sulfur hexafluoride (SF6), at a moderate
pressure for phase to phase and phase to ground insulation. The high-voltage conductors, circuit breaker
interrupters, switches, current transformers, and voltage transformers are encapsulated in SF6 gas inside
grounded metal enclosures. The atmospheric air insulation used in a conventional, air-insulated sub-
station (AIS) requires meters of air insulation to do what SF6 can do in centimeters. GIS can therefore be
smaller than AIS by up to a factor of ten. A GIS is mostly used where space is expensive or not available.
In a GIS, the active parts are protected from deterioration from exposure to atmospheric air, moisture,
contamination, etc. As a result, GIS is more reliable, requires less maintenance, and will have a longer
service life (more than 50 years) than AIS.
