Al ₂ O ₃ , an insulating ceramic with excellent mechanical and thermal properties, has been a kind of ideal fillers for composites. However, due to its poor charge transport capacity, composites doped with Al ₂ O ₃ have a bad surface insulation property. In this study, nano-Al ₂ O ₃ particles were modified by plasma fluorination using dielectric barrier discharge, and then doped into epoxy resin to prepare composites. In the preparation stage, the plasma treatment with and without fluorine were differentiated to determine whether fluorine or plasma itself had an influence on the microstructure of Al ₂ O ₃ . The changes of dielectric and surface insulation properties of composite materials before and after filler fluorination were studied. The variation of dielectric constant as a function of filler content has presented a Z-shape curve. Both larger particle diameter and fluorination treatment can reduce the value of dielectric constant, and lead the curve to a monotonous increasing trend. A model of dielectric distribution by the finite element method was constructed to explain the variation. Before fluorination treatment, the flashover voltage as a function of filler content presents a multi-inflection variation. After fluorination, the surface charge dissipation capacity together with flashover voltage were enhanced, and the fluorination treatment could increase the flashover voltage by up to 34.7% of the pure epoxy. The modification process and test results are of guiding significance for improving the insulation properties of epoxy composites.

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.

Organophilic groups of coupling agents can be the key factor for the electrical performance of Boron Nitride (BN)/meta‐aramid composite paper. In this article, four types of triethoxy‐silane coupling agents with different organophilic groups, including mercapto‐propyl (MP), glycidylether‐propyl (GP), amino‐propyl (AP) and trideca‐fluoro‐octyl (TFO) were studied. The structural and electrical properties of modified papers were compared, and the molecular simulation was conducted to reveal the interface interaction of modified BN and aramid. The results show that AP, GP and MP follow the same mechanism, improving the electrical performance by modifying the interface stability and paper structure, and the ranks of improving effects are AP, MP and GP. While, TFO mainly relies on the fluorine components to implement the electrical reinforcement, which compensates for the shortcoming in the paper structure. By choosing TFO and filler content of 15 wt%, the optimal breakdown strength of the paper can be increased to 28.17 kV/mm, 1.8 times that of the paper doped with the hydroxylated BN.

This study investigates the impact of interface defects on the electrical performance of epoxy-impregnated aramid papers. Various composites with different degrees of defects were prepared and analyzed for their structural, mechanical, partial discharge, and insulation performance. The results demonstrate the widespread presence of void defects in the composites, negatively affecting paper compactness, mechanical properties, initial discharge voltage, and leading to significant gas gap discharge phenomena. In terms of insulation performance, composites with severe defects exhibit a 40-fold increase in low-frequency dielectric loss, a 16-fold increase in electrical conductivity, and up to a 64% reduction in breakdown field strength, along with noticeable shallowing of charge traps. Phase field modeling of electro-thermal breakdown reveals that void-type defects guide discharge trajectories, causing lateral damage diffusion, localized overheating, and severe electric field distortion, ultimately endangering the voltage resistance. This study provides the research support for the application of aramid paper as a matrix for a novel epoxy-impregnated insulating paper.

The morphologies and velocity of ionic wind induced by direct-current (DC) corona discharge were experimentally measured. DC voltage was applied to short air gaps of high-voltage electrode–needle electrode and grounding electrode–net electrode to generate coronas, so as to allow the generation of ionic wind induced by corona discharge. The purpose of the study is to optimise the multi-needle-to-net electrode structure to improve the velocity of the ionic wind and keep it in a relatively stable state. For this purpose, the influences of various parameters on the velocity of the ionic wind were explored. The research results showed that the side length of meshes and the distribution mode of needles significantly affected the velocity of the ionic wind. The maximum velocity of the ionic wind, when the side length of meshes was 0.85 mm was 3 and 1.28 times those when the side lengths of the meshes were 2 and 0.425 mm, respectively. This indicated that there was an optimal side length that can maximise the velocity of the ionic wind. Increasing the number of needles and optimising the distribution mode of needles can effectively improve the velocity, that is, the improvement of the number and distribution uniformity of needles was conducive to increase the velocity of the ionic wind. Increasing the voltage amplitude can increase the velocity of the ionic wind, however, it was possible that noise was significant and in this case, the corresponding voltage cannot be considered as the working voltage of the ionic wind generator.