Development of 72-kV high-pressure air-insulated GIS with vacuum circuit breaker

Abstract

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 (www.interscience.wiley.com). DOI 10.1002/eej.20451