Gas Insulated Substations (GIS) is a compact,multicomponent assembly enclosed in a ground metallic housing in which the primary insulating medium is compressed Sulphur hexafluoride (SF6) gas.
SF6 acts as an insulation between live parts & the earthed metal closure. Gas insulated switchgear is used in industrial areas to fulfil high-energy demands by space saving design with a minimum of cost. SF6 switchgear installed in Canada in a 550 kV substation with 100 kA.
Gas insulated substations are particularly suitable for underground construction beneath public buildings. Gas insulated substation mainly used for a power transmission system or a sub-station system, of which outgoing bus bar is shortened to reduce consumption of the outgoing bus bar Sulfur Hexafluoride.
Its a colorless, odorless, non-toxic, liquified gas. Shipped as a liquid under its own vapor pressure. Sulfur Hexafluoride gas, which is itself inert.It disassociates in the presence of an RF field to form reactive fluorine ions. SF6acts as an insulation between live parts & the earthed metal closure.The dielectric strength of SF6 gas at atmospheric pressure is approximately three times that of air. Pace requirement is only 10 to 25 percent of what is required is a conventional substation.
SF6 can be prepared from the elements through exposure of S8 to F2. This is also the method used by the discoverers Henri Moissan and Paul Lebeau in 1901.It does not react with molten sodium, but reacts exothermically with lithium. Of the 8,000 tons of SF6 produced per year, most (6,000 tons) is used as a gaseous dielectric medium in the electrical industry, it has a much higher dielectric strength than air or dry nitrogen.
This property makes it possible to significantly reduce the size of electrical gear.
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