Influence of Low Temperature Plasma Treatment on Surface Insulation Performance of Polyimide Film

The polyimide film on the ultra-high voltage equipment may be exposed to plasma during operation, and the flashover characteristics may be affected by complex charging conditions along the surface. In order to evaluate the insulation state of polyimide film, the flashover characteristics of polyimide before and after plasma treatment under DC high voltage condition were studied in this paper. First, low temperature plasma was generated by dielectric barrier discharge (DBD) in argon to treat polyimide films, and then four groups of film samples were obtained by changing the treatment time (Os, 30s, 60s, 90s). And then, the samples were observed and compared based on Scanning Electron Microscope and Fourier Transform Infrared spectroscopy; moreover, the surface potential decay property, surface conductivity and DC surface flashover voltage were also measured and analyzed. The experiment reported that with the increase of plasma treatment time, the surface roughness of polyimide increases, and the functional groups are introduced in on the surface; the surface conductivity of the sample increases, and the trap density decreases; the flashover voltage increases. At last, analysis was conducted based on SEEA model and ETPR model. On the one hand, plasma treatment improves the roughness of PI film, inhibits the initial and development process of secondary electron emission, and improves the flashover voltage. On the other hand, with the increase of processing time, the trap density decreases, which cause the increase of surface conductivity. Therefore, it is hard to form the electron and hole trap centers, which is the establishment of dielectric polarization. Thus, the flashover voltage increases. The experimental results provide a set of methods for evaluating the surface flashover characteristics of polyimide under plasma exposure.