Measurement method and accumulation characteristics of surface charge distribution on polymeric material under DC voltage

Charge accumulation on a solid insulator surface is one of the critical factors for the development of dc gas-insulated equipment since it will lead to the overstress of polymeric insulation due to local field distortion and enhancement. Therefore, it is significant to study the charge accumulation phenomenon on spacer surface under dc field. However, it remains an important subject to obtain the accurate results of surface charge distribution. Electrostatic probe method was used to measure the surface potential distribution of a cone-shaped spacer in a downsized gas-insulated line (GIL) and the inverse calculation method of the surface charge distribution, especially for this "shift-variant" configuration, was investigated. Numerical simulation was used to obtain the transfer matrix from charge density to the probe output. By a signal processing technique based on the Wiener filter, the ill-condition problem of the matrix was solved and the stability of the calculation was improved. The study also analyzed the spatial resolution and accuracy of the calculation results, which shows that the spatial resolution of the system can reach 1.8 mm. Based on the above method, we studied the charge accumulation phenomena of the epoxy spacer under dc voltage in air and SF₆. The results show that there are two patterns in the charge distribution: "dominant uniform charging" and random "charge speckles". The uniform charging was of the same polarity as the applied voltage, which indicates current flow from the solid bulk is the dominate mechanism in surface charging.