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 (CTs), and voltage transformers (VTs) are encapsulated in SF6 gas inside grounded metal enclosures. The atmospheric air insulation used in a conventional, air-insulated substation (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 10. 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.
