Abstract
SF6 is used as the main insulation gas for gas-insulated switchgear (GIS), but it has recently become a gas that must be restricted because of its greenhouse effect. To date, we have studied the insulation characteristics of compressed N2 and CO2 as a possible alternative for SF6. We have reported that N2 or CO2 must be pressurized up to 2.0MPa when it is used as a substitute for SF6 of 0.5MPa. Therefore, we have proposed a hybrid insulation composition that uses the gas and solid insulators. Because the central conductor of GIS is the covered by solid insulator in this composition, the high-pressure gas of 2.0MPa is not needed. However, the joint of the solid insulator becomes the weak point for discharge development. In this paper, we describe the effective configuration for the improvement of withstand voltage on the basis of the experiment. As a result, the most effective connector was made of resin without an implanted electrode and the configuration was the case without the solid-solid interface between the solid insulator of the central conductor and the resin connector. In this experiment, the improvement of the breakdown electric field of the hybrid composition was 44% or more compared with the case of only gas insulation (conventional method). In addition, a further improvement can be expected by optimizing the insulation creepage distance and configuration.
