Sulfur Hexafluoride and Its Uses

First of all, what is sulfur hexafluoride (SF6)? SF6 is a non-toxic, nonflammable and noncorrosive gas. SF6 has almost the same chemical properties of a noble gas and it does not react with other materials. Under standard conditions, SF6 is colorless and odorless gas in high electrical components. Furthermore, SF6 also inhibits surface erosion and oxidation. It has high partial vapor pressure at both normal and low temperatures. SF6 also has an excellent heat transfer. Its high molecular weight and low viscosity enable SF6 to transfer heat more efficiently by convection. SF6 gas performed as an excellent insulating and arc-quenching. Therefore, it used as an interrupting medium in switchgear and circuit breakers instead of oil and air because it can improve the power system reliability. SF6 can be used in different types of electrical switchgear such as Gas Insulated Switchgear (GIS). SF6 gas not only as arc-quenching medium but as insulation as well. With respect to the SF6 insulating gas pressure, there are two principal GIS designs: high pressure GIS functioning at about 405kPa, and low pressure GIS which is operating at 120kPa. While at higher voltage levels, the advantages of high pressure GIS become dominant. But the more suitable design is below the low pressure GIS at a rate voltage of 72.5kV. A higher SF6 gas pressure will increase the dielectric strength. As a result, for a given voltage level the required conductor spacing is reduced, resulting at a more compact design.
Due to the economical and functional reasons, high voltage switchgear with SF6 gas is commonly used. The replacement of SF6 with air and oil in high voltage switchgear is because SF6 gas has the outstanding characteristics of the gas with the gas-tight metal enclosure. Some features like low operating energy for the switching devices, no risk of fire and not toxic hazard are available. Besides that, the space occupied by the switchgear is absolutely decreased and easier to install in