• SF6 alternative gases;
  • air;
  • SF6-free GIS;
  • vacuum circuit breaker


SF6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas-insulated switchgear (GIS). However, use of SF6 gas has become regulated under agreements set at the 1997 COP3. Thus, investigation and development for GIS with a lower amount of SF6 gas are being carried out worldwide. Presently, SF6-free GIS has been commercialized for the 24-kV class. Air or N2 gas is used as the insulation gas for this GIS. On the other hand, SF6-free GIS has not been commercialized for the 72-kV-class GIS. The dielectric strengths of air and N2 gas are approximately one-third that of SF6 gas. To enhance the insulation performance of air and N2 we have investigated a hybrid gas insulation system which has the combined features of providing an insulation coating and suitable insulation gas. We have developed the world's first 72-kV SF6-free GIS. This paper deals with key technologies for SF6-free GIS, such as the hybrid insulation structure, a bellows for the high-pressure vacuum circuit breaker, a newly designed disconnector and spacer, and prevention of particle levitation. Test results of the 72-kV high-pressure air-insulated GIS with the vacuum circuit breaker are described. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 13–23, 2006; Published online in Wiley InterScience ( DOI 10.1002/eej.20451