Gas insulated substations (GIS) have been used in power systems over the last three decades because of their high reliability, easy maintenance, small ground space requirement etc. This article is an introduction to Gas insulated Substations.Gas Insulated Substation (GIS) also called SF6 Gas Insulated Metalclad Switchgear is preferred for 12kV, 36kV, 72.5kV, 145 kV, 245 kV, 420 kV and above voltages.
In a GIS substation, the various equipment like Circuit Breakers, Bus bars, Isolators, Load break switches, Current transformers, Voltage transformers, Earthing switches etc. are housed in separate metal enclosed modules filled with SF6 gas. The SF6 gas provides the phase to ground insulation.
As the dielectric strength of SF6 gas is higher than air, the clearances required are smaller. Hence the overall size of each equipment and the complete sub-station is reduced.
The various modules are factory assembled and are filled with SF6 gas. Thereafter, they are taken to site for final assembly.
SF6 Gas Insulated Substations are compact and can be installed conveniently on any floor of a multi storeyed building or in an underground sub-station. As the units are factory assembled, the installation time is substantially reduced.
Such installations are preferred in composition cities, industrial townships, hydro stations where land is very costly.
Higher cost of SF6 insulated switchgear is justified by saving to reduction in floor-area requirement.
SF6 insulated switchgear is also preferred in heavily polluted areas where dust, chemical fumes and salt layers can cause frequent flashovers in conventional outdoor sub-stations.
The GIS require less number of lightning arresters than a conventional one. This is mainly because of its compactness.
Why SF6 is Used?
Inside a Gas Insulated Substation (Video)
Advantages of Gas Insulated Substations
Compactness of GIS
Protection from pollution
The construction of the building need not be very strong like conventional power houses.