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SUMMARYSF 6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas-insulated switchgear (GIS). However, use of SF 6 gas has become regulated under agreements set at the 1997 COP3. Thus, investigation and development for GIS with a lower amount of SF 6 gas are being carried out worldwide. Presently, SF 6 -free GIS has been commercialized for the 24-kV class. Air or N 2 gas is used as the insulation gas for this GIS. On the other hand, SF 6 -free GIS has not been commercialized for the 72-kV-class GIS. The dielectric strengths of air and N 2 gas are approximately one-third that of SF 6 gas. To enhance the insulation performance of air and N 2 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 SF 6 -free GIS. This paper deals with key technologies for SF 6 -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.

SF 6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas insulated switchgear (GIS). However, use of SF 6 gas has become regulated under agreements set at the 1997 COP3. So investigation and development for GIS with a lower amount of SF 6 gas are being carried out worldwide. Presently, SF 6 gas-free GIS has been commercialized for the 24 kV class. Air or N 2 gas is used as insulation gas for this GIS. On the other hand, SF 6 gas-free GIS has not been commercialized for 72 kV class GIS. Dielectric strengths of air and N 2 gas are approximately 1/3 that of SF 6 gas. So to enhance insulation performance of air and N 2 , 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 SF 6 gas-free GIS. This paper deals with key technologies for SF 6 gas-free GIS such as the hybrid insulation structure, bellows for the high pressure vacuum circuit breaker, a newly designed disconnector and spacer and prevention of particle levitation. Test results of 72 kV high pressure air-insulated GIS with the vacuum circuit breaker are described.

Radial distributions of plasma density change significantly at pressures above and below 0.2 Torr. At 0.5 Torr, the discharge is almost hollow with high density around the edge, and its color is almost white. At 0.1 Torr, the density distribution becomes high in the central region both axially and radially, and the discharge color becomes yellowish white. Two prominent lines of optical emission show different spatiotemporal profiles. The O2 + 559.8 nm line is bright in the central region, while the O I 777.2 nm line is bright just in front of the instantaneous cathode.

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