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Charges accumulated on the dielectric surface under DC field can lead to the overstress of the insulator due to the local field distortion, and may even initiate the surface flashover. Therefore, it is very necessary to study the surface charge accumulation and decay on polymer materials under DC voltage in order to get a theoretical basis for the design of DC composite insulators, considering that polymer materials are widely used in the electrical field. Since then, this paper chooses silicon rubber as the study object and focuses on the accumulation and decay of surface charge on it.
Since the output of the Kelvin probe is the electric potential instead of the charge density. In this paper, the general principle of the surface charge calculating method is analyzed based on the active capacitance probe method and the image processing technique. The experimental subject is a shift-invariant system and the transfer function matrix H is simplified based on the properties of it. Furthermore, two-dimensional Fourier transform and Wiener filter techniques are applied in this paper, thus the relationship between potential and charge density can be processed in spatial frequency domain. Afterwards, the accuracy of the measurement and inverse algorithm are verified by Dust Figure Method.
On the one hand, the surface charge accumulation is rapid and surface potential reaches nearly the applied voltage on the silicon rubber material which has a quite serious accumulation charge distribution. On the other hand, we inject charge into the surface of the silicon rubber sample by using a needle-plate electrode to study the decay phenomenon. The study is conducted under different humidity conditions, which reaches that the surface charge mainly decays by volume resistivity under low humidity and the initial surface charge distribution changes its shape when decay process occurs in high humidity air.
