Surface charge Accumulation on Epoxy Insulator with Metal Particle in C4F7N/CO2 under AC voltage

Metal particles on the epoxy insulator of gasinsulated switchgear (GIS) have been considered as a critical factor leading to severe surface charge accumulation. This paper reports on the charge distribution behavior on a downscaled insulator in heptafluorobutyronitrile C
4
F
7
N and carbon dioxide CO
2
mixture with a linear metal particle under AC voltage. In this study, the metal particle was placed on the grounded electrode, the high-voltage electrode, and the middle area of the insulator surface, and a case without metal particle was implemented. The potential measurement device scanned the insulator surface at 20,40, and 60 minutes of applied voltage and the obtained potential were converted into charge density by the inversion algorithm. The results showed that the surface charge on the insulator was mainly negative and the shape of the charge distribution was almost unchanged as time increased. However, the characteristics and polarity of the charge speckles varied when the metal particles were placed at different positions on the insulator surface.