Optimization of a cathode configuration in gas insulated switchgear with a permittivity graded insulator

An application of a functionally graded material (FGM) to the solid spacer in gas insulated switchgears (GISs) can reduce the electric field intensity. Especially, the location of the high electric field concentration moves from the anode to the interface between the spacer and the gas, when the FGM spacer is used. However, the electric field stress near the triple junction of the cathode with a rounded shape, which remarkably affects the insulation capability of a GIS, increases reversely. Therefore, in order to prevent this, it is necessary to modify the cathode geometry in the common C-GIS. In this research, we dug a groove in the cathode near the triple junction, and performed the optimization of this cathode configuration by using the design of experiments (DOE). Additionally, the permittivity graded spacer with the permittivity variation of a reverse direction distribution unlike that of the existing unidirectional or bidirectional distribution was applied. Consequently, both the maximum electric field intensity generating near the inflection point of the spacer geometry and the electric field stress near the triple junction of the cathode can be efficiently reduced by using the FGM spacer and designing the optimal cathode shape.