A study of voltage withstand of various gases under AC voltage

At present, equipments in Gas Insulated Substation(GIS) such as circuit breaker, ground switch, busbar and transformer use SF₆ as its insulation because of its better electrical withstand, less area for installation and arc quenching for circuit breaker. However, SF₆ has high cost. Furthermore, it causes green house effect and poisonous environment. In this research, the voltage withstand of Ar, He, O₂, CO₂, Air, and N₂ was studied to compare with that of SF₆. The voltage withstand of each gas under 50 Hz AC voltage was studied using a chamber designed following ASTM D 2477-96 which consists of rod-plane and sphere-plane gap made of stainless steel. Gap distances in this experiment were 5, 10, 15 and 20 mm while the gas pressures were varied to 1, 2 and 3 bars. The results show that He has the lowest voltage withstand compared to other gases at the same gap distance and pressure.