It is located in a sealed gas tank from the main busbar connection point to the cable connection point, and SF6 (Sulfur Hexafluoride) is used as the gas. SF6 gas is a colorless, odorless and non-flammable greenhouse gas with high dielectric strength. SF6 gas has high electrical and chemical stability. It is used in many areas today due to its heat conduction and arc extinguishing performance.