Gas-Insulated Substation (GIS) at the Norochcholai Coal Power Plant in Sri Lanka.
A gas-insulated substation (GIS) uses a superior dielectric gas, SF6, at moderate pressure for phase-tophase and phase-to-ground insulation. The high voltage conductors, circuit breaker interrupters, switches, current transformers, and voltage transformers are 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 the deterioration from exposure to atmospheric air, moisture, contamination, etc.
Gas Insulated Substation (GIS) at the Norochcholai Coal Power Plant in Sri Lanka
Gas Insulated Substation (GIS) Protection Panel Room at the Norochcholai Coal Power Plant in Sri Lanka
Gas Insulated Substation (GIS) switch yard at the Norochcholai Coal Power Plant in Sri Lanka
Electricity generated at the Norochcholai Coal Power Plant being connected to the National Grid
Special Thank to Eng. K. A. Nishantha Perera, Operation Engineer, Norochcholai Coal Power Plant, Sri Lanka.
Reference : Electrical Engineering Portal & GIS Presetaition by Mohd. Zuhaib, Mohammad Sharique Alam & Junaid Ahmed
Sulphur Hexaflouride (SF6) gas : the primary insulating medium.
(SF6) gas- superior dielectric properties used at moderate pressure for phase to phase and phase to ground insulation.
Preferred for voltage ratings of 72.5 kV, 145 kV, 300 kV and 420 kV and above.
Various equipments like Circuit Breakers, Bus-Bars, Isolators, Load Break Switches, Current Transformers, Voltage Transformers, Earthing Switches, etc. housed in metal enclosed modules filled with SF6 gas.
SF6 - Gas used in GIS
Sulfur hexaflouride is an inert, nontoxic, colorless, odorless, tasteless, and nonflammable gas consisting of a sulfur atom surrounded by and tightly bonded to six flourine atoms. It is about five times as dense as air. SF6 is used in GIS at pressures from 400 to 600 kPa absolute. The pressure is chosen so that the SF6 will not condense into a liquid at the lowest temperatures the equipment experiences.
SF6 has two to three times the insulating ability of air at the same pressure. SF6 is about 100 times better than air for interrupting arcs. It is the universally used interrupting medium for high voltage circuit breakers, replacing the older mediums of oil and air. SF6 decomposes in the high temperature of an electric arc, but the decomposed gas recombines back into SF6 so well that it is not necessary to replenish the SF6 in GIS.
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