Alumina/epoxy resin (Al 2 O 3 /EP) composite material is widely used in the manufacture of insulators. However, the operation environment of long-term high-voltage direct current will destroy Al 2 O 3 /EP surface insulating performance. In this article, Al 2 O 3 /EP was modified by atmospheric pressure Ar and Ar/CF 4 plasma jet, and its aging effect was studied by investigating the physicochemical characteristics and the electrical performances of the sample 0 $ 100 days after modification. The experimental results show that after plasma treatment the surface roughness of the material increases; the O/C ratio on the surface of the material increases after Ar treatment, and the F element is grafted on the surface after Ar/CF 4 treatment. These changes lead to the increase of surface energy and hydrophilicity, and the improvement of electrical performance. The surface properties change within 100 days owing to the oxidation reactions and the variability of recombination chemical bonds and molecular chains after high-energy plasma treatment. The surface O/C ratio of the materials treated by Ar plasma is obviously reduced, the hydrophobicity is restored to some extent, and the electrical properties are also obviously weakened. In comparison, the properties of Ar/CF 4 plasma-modified materials do not change significantly.

In this paper, plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface. The physicochemical characteristics of samples are investigated and the electrical performances measured. The obtained results show that compared with untreated and single treated samples, the samples treated by step gradient modification significantly improve the flashover performance. According to experiment and simulation, the mechanism explanations are summarized as follows. First, it is found that the step gradient conductivity can effectively optimize the electric field distribution of a needle-needle electrode. Then, step gradient modification suppresses the accumulation of surface charge at the triple junction and makes the charge distribution more uniform. Furthermore, it can accelerate the surface dissipation on a high electrical field region and control the dissipation rate on a low electrical field region. All these results can restrain surface discharge and increase the flashover voltage. The step gradient modification method proposed in this paper provides a new idea for improving the surface insulation performance.

Epoxy resin (EP) tends to accumulate a large amount of charge on its surface when exposed to a high-voltage DC electric field, which leads to a reduction in its insulative performance and an increase in potential safety risks in power systems. To suppress charge accumulation, improve the flashover voltage of the EP, and reduce the risk of gas insulated switchgear (GIS) / gas insulated transmission line (GIL) failure, we used two plasma-etching methods, i.e., atmospheric-pressure dielectric barrier discharge (DBD) and the atmospheric-pressure plasma jet (APPJ), to modify the surface of the EP. The surface morphology and electrical properties of the modified materials were explored as a function of time. The results show that after DBD treatment, the roughness of the sample increases by 103.9 nm, the conductivity increases by 3.9×10 -18 S, and the flashover voltage increases by 14.4%; after APPJ treatment, the roughness of the sample increases by 223.5 nm, the conductivity increases by 3.4×10 -17 S, and the flashover voltage increases by 18%. This shows that both plasma-etching methods can improve the insulation properties of materials by improving the surface-charge characteristics. The two methods are compared with each other: the APPJ treatment method is better at improving the surface roughness and electrical properties of materials, and this flexible treatment method has greater potential in industrial applications.

Alumina/epoxy composites are widely used in the manufacture of basin insulators, but their surfaces tend to accumulate charges under the high-voltage direct current (HVDC), which induce the decline of surface insulating property. In this article, the modification method of depositing ZrO 2 film sprayed by plasma atomization was proposed to improve the surface insulation performance of the material. Argon was used as the plasma discharge gas, and ZrO (NO 3) 2 .xH 2 O was used as the zirconium source. The morphology, surface roughness and the element content of materials were measured, and the surface conductivity, flashover voltage, and charge characteristics of the treated samples were tested. The experimental results displayed that a zirconia film was formed on the epoxy resin surface, which restrain the accumulation of surface charges. The surface conductivity of the modified sample was improved by 3 to 4 orders of magnitude, and the flashover voltage was increased by 20%. Studies have shown that: ZrO 2 film sprayed by plasma atomization can improve the insulation performance of epoxy resin surface, and it provides an effective method for the surface modification of insulating materials.