Electric field grading of gas insulated switchgears with microvaristor composites

This paper reports a new field grading method for GIS (gas insulated switchgear) insulators with the non-linear resistive material (NRM) composed of epoxy and microvaristors. NRM should be carefully used for GIS insulators, because the electric field applied to GIS insulators is much higher than that to the air-insulated insulators and there is a possibility that NRM might be damaged due to the excessive stress. The simulation on the field grading effect on a GIS insulator was carried out with the various NRM characteristics based on the measured characteristics of NRM samples. The authors show that NRM has the good field grading effect by both the high dielectric and non-linear resistance and also propose a way of selecting the suitable NRM characteristics.