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Accumulation Characteristics of Surface Charge on a Cone-type Model Insulator under DC Voltage

Surface charge accumulation on the insulator has retarded the development of DC gas-insulated equipment, since it will distort and enhance the local field strength and help to initiate the surface flashover. Therefore, it is significant to study the surface charge accumulation phenomenon on the insulator under DC field. In this paper, Kelvin probe method is adapted to measure the surface potential distribution of a cone-type insulator in a downsized gas-insulated transmission line (GIL) after being applied by DC voltage. Meanwhile, inversion calculation is applied to obtain the surface charge density distribution. Results have shown that there exist two patterns in the charge distribution: uniform charging and charge speckles. The polarity of the uniform charging is the same as that of the the applied voltage, indicating that current flow from the bulk of the solid is the dominate mechanism in surface charging. Highly localized pockets of charge are also observed, which are referred to as speckles. They may originate from the attached tiny particles on the insulator surface or defects at the triple-junction points. The proposed two patterns provide a new perspective for the research of surface charge accumulation.