Design of solid/gas composite insulation system with embedded electrode

Solid insulated switchgear (SIS) has been developed as a substitution for sulfur hexafluoride gas insulated switchgears in the medium voltage class. Its main circuit including a vacuum interrupter is coated with epoxy resin. An embedded electrode was employed in order to enhance the surface insulation performance for further miniaturization and higher stress design. In the previous studies, the surface insulation performance was examined by using a model electrode system which modified the electrode system of the moving part of SIS and the estimation method of the surface breakdown voltage was proposed. In addition, the simulation of the surface breakdown characteristics of a model electrode system was conducted and a design method was proposed. In the present study, the insulation performance of the solid part was taken into account and the insulation design was conducted using the proposed design method. The "equivalent insulation distance" was introduced and the partial discharge inception field strength was also taken into account. The insulation design was done for 22, 33 and 77 kV systems and the values of the design parameters were provided. In addition, it was found that two different types of the design concepts were available.