Imaging System Design And Measurement Of Surface Charge For Disc Insulator With Complex Surface Profile

Epoxy casting insulator has been widely employed in Gas Insulated Switchgear（GIS）and Gas Insulated transmission Line（GIL）.The charge accumulation on insulator surface under DC voltage has become an important factor to induce flashover and reduce the performance of insulator.A surface charge imaging system of disc insulator with complex surface profile was designed in this paper.The distribution of surface charge was imaged through the coordination of software and hardware.The influence of gas environment and metal particle contamination on surface charge accumution was investigated.The mechanism of surface charge accumulation and the effectiveness of the system was discussed on the basis of surface charge accumulation simulation.The main work of this paper is as follows,1.A disc insulator employed in real GIS/GIL was taken as the research object.In order to simulate the electric field and gas environment inside the GIS/GIL,a sealed chamber and coaxial structure electrides were designed.Accordingly,the insulator could be charged with coaxial electric field in air,vacuum,SF₆/N₂ and other atmospheres.A surface potential measurement apparatus was constructed,by which the electrostatic probe was driven by a combination of shifting and rotating platforms to scan the complex surface and obtain the surface potential distribution of the insulator.2.Two surface potential sampling schemes,i.e.high-speed/low-precision and low-speed/high-precision,were designed.The sampling intervals in the radial and the circular directions are 8 mm/10°and 4 mm/5°,respectively.Based on COMSOL Multiphysics software,the inversion calculation was carried out by appling the charge simulation method.The Tikhonove regularization method was employed for inversion calculation of point spread function matrix and the surface charge density distribution was obtained.Furthmore,the three-dimensional coordinate matrix of insulator surface was established,and the charge density ditribution were imaged on the three-dimensional surface of insulator.3.The effects of gas environment（air,vacuum and SF₆/N₂）and metal particles on the surface charge distribution behavior of the disc insulator under DC voltage were investigated.It was found that positive charges were accumulated on non-planar region of insulator surface in shape of charge speckle in air environment.The average charge density profile showed a double-peak distribution.The negative charges were accumulated on local region of insulator surface in vacuum.The average charge density profile showed a complex distribution of single-peak superimposed by fluctuation.And negative charge was mainly accumulated on insulator surface in SF₆/N₂.However,a few positive charges were accumulated concentratly in local region of insulator surface.The average charge density profile also showed a complex distribution of single-peak superimposed by fluctuation.The simulation of surface charge accumulation showed that the competition of bulk conduction,gas conduction and surface conduction resulted in the charge distribution.And,as the metal particles connecting with the grounding electrode,the distribution behavior of surface charge changed significantly.