is a kind of insulating ceramics with high rigidity and melting point, which has been widely used in the preparation of basin-type insulators [1]. Meanwhile, Al 2 O 3 is one of the most commonly used fillers for composites [2]. Filling nano-Al 2 O 3 can improve the mechanical strength [3-6], thermal stability [7,8], wear resistance [9, 10] and other properties of composite materials, but the improvement of surface insulation performance is not obvious [11,12].
Epoxy resin filled with micron alumina (micro‐Al2O3/ER) has been widely used in the manufacture of basin insulators for its excellent mechanical and thermal properties. However, charge dissipation properties of micro‐Al2O3/ER are too poor to ensure its surface insulation on strength under long‐term action of a DC electric field. In this paper, the modification method of plasma cohydrothermal fluorination of filler was proposed to improve its surface charge dissipation performance. The surface morphology and the element content of Al2O3 were observed, and the flashover voltage and charge characteristics of different composites were tested. Finally, the trap distribution was calculated by isothermal current attenuation method. Self‐comparison analysis with single‐step modification of plasma treatment shows that the cofluorination method has a high graft rate of fluorine element and an ideal modification effect on surface insulation, with its technical means convenient to be applied in the insulator manufacturing industry.
This work treats the Al 2 O 3 -ER sample surface using dielectric barrier discharge fluorination (DBD-F), DBD silicon deposition (DBD-Si), atmospheric-pressure plasma jet fluorination (APPJ-F) and APPJ silicon deposition (APPJ-Si). By comparing the surface morphology, chemical components and electrical parameters, the diverse mechanisms of different plasma modification methods used to improve flashover performance are revealed. The results show that the flashover voltage of the DBD-F samples is the largest (increased by 21.2% at most), while the APPJ-F method has the worst promotion effect. The flashover voltage of the APPJ-Si samples decreases sharply when treatment time exceeds 180 s, but the promotion effect outperforms the DBD-Si method during a short modified time. For the mechanism explanation, firstly, plasma fluorination improves the surface roughness and introduces shallow traps by etching the surface and grafting fluorine-containing groups, while plasma silicon deposition reduces the surface roughness and introduces a large number of shallow traps by coating SiO x film. Furthermore, the reaction of the DBD method is more violent, while the homogeneity of the APPJ modification is better. These characteristics influence the effects of fluorination and silicon deposition. Finally, increasing the surface roughness and introducing shallow traps accelerates surface charge dissipation and inhibits flashover, but too many shallow traps greatly increase the dissipated rate and facilitate surface flashover instead.
NanoTiO 2 /epoxy resin composites, a kind of dielectric materials with excellent thermal, mechanical and electrical properties, has extensive promise in the insulation area of power system. Although the semiconductor property of TiO 2 filler can suppress the electric field mutations in the epoxy insulation devices, the doping of TiO 2 will have bad influence on the charge transmission, thus weakening the surface insulation. To solve this problem, filler fluorination with dielectric barrier discharge (DBD) plasma and chemical methods were designed to modify the TiO 2 filler. The effects of two fluorination methods on the micro-structures, electrical parameters, and insulation properties of the materials were studied. The results have shown that both DBD plasma and chemical fluorination methods can effectively introduce fluorine into TiO 2 filler and its epoxy composites, decreasing its dielectric constant and volume resistivity. Through doping the fluorinated TiO 2 nanoparticles, the direct current flashover voltage and charge dissipation rate of the composites can be at best increased to 1.5 times and 4.6 times of the pure epoxy, respectively. The enhanced surface insulation properties were explained by the trap effect and the change of electrical parameters (containing dielectric constant and volume conductivity) brought by fluorination treatments. The study results of two types of filler fluorinations have guiding significance for nano-modification of epoxy insulation composites.
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