What is a Gas Insulated Switchgear/GIS

Gas Insulated Substation:-
Gas insulated substation (GIS) consist of components where active parts on high voltage potential are located in the middle of the aluminum alloy pipes and held in this location by epoxide resin insulators. The pipes are filled in with insulating gas and have earth potential. The GIS consists of typical HV components such as disconnectors, CBs, busbars, and voltage and current transducers. GIS can save up to 90% of space compared with air-insulated substations. It is particularly suitable for indoor and outdoor applications.
Technology Types
The technology type of GIS is defined by:
The insulation gas:
SF6
SF6 mixture with N2
SF6 free
The phase arrangement:
one phase per pipe
three phases per pipe
The voltage level
Application type:
indoor
outdoor
Components & enablers
N/A
Advantages & field of application
The GIS is applied in cases where the available space is very limited or the substations require complex connections. The single bays and busbars can be arranged very tightly because they are on earth's potential. The GIS can be connected to overhead lines by bushings and to cables by special cable connectors.
Indoor GIS are mostly maintenance-free components that have higher reliability compared to air-insulated substations (AIS). Nevertheless, the total availability of GIS is comparable to AIS because of significantly longer (many weeks) repair times after a failure.
The GIS with non-SF6 gas appeared recently on the market. The major advantage of non-SF6 gases is their very small or non-existing global warming potential. Therefore, two different applications need to be considered:
non-SF6 gas is used for insulation only (up to 420 kV)
non-SF6 gas is used for insulation and arc quenching (up to 170 kV)
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