Due to scarcity and high price of land, Gas Insulated Switchgear Substations are gaining popularity in India in many other countries. It consumes much smaller space comparing to outdoor switchyards. All switchgear components like CB, isolator, CT, PT, LA bus bars are mounted in SF6 gas filled metallic chambers. Since SF6 gas under pressure provides much better insulation than air, the phase to phase and phase to earth clearances reduce considerably resulting in very compact design of switchgears. Because of completely sealed design maintenance is much less and hence needs lesser number of operating staff.
GIS type switchgears are normally placed indoors. Each bay of the GIS has its own Local Control Panel (LCP) which under Test and Maintenance mode houses the operating switches, indications, mimic, meters and most importantly the interface terminals for wiring between the LCP and the Remote Control and Relay panels.
Hybrid GIS type Substations (132kV, 220kV) are also being used by some utilities, specially where 1) Ease of maintenance of the open type switchyard is difficult due to harsh environmental conditions (snow, dust etc.), 2) There is space constraint. As shown in the photo, Hybrid GIS encapsulates Circuit breaker, Disconnects, Earth switches, Current transformers in one common SF6 gas filled enclosure having SF6 to Air busings for connection with bus bars one one side and the outgoing Line gantry / Power Transformer on the other side. Hybrid GIS helps to optimise the space requirement of the Substation and reduces maintenance requirement of the equipment since the bay equipment are mostly not exposed to atmosphere.