During the operation of multi-electric aircraft, the polytetrafluoroethylene (PTFE) material used to insulate the aviation cable is subjected to a high electric field while working under the extreme conditions of high temperatures for a long time, which can easily cause a partial discharge and even flashover along the surface, which seriously threaten the safe operation of the aircraft. In this paper, the electrical insulation properties of PTFE were regulated via modification by the magnetron sputtering of TiO₂ under high temperatures, and modified PTFE with different sputtering times was prepared. The direct current (DC) surface discharge, surface flashover, and electric aging characteristics of modified PTFE were studied under the condition of 20~200 °C, and the mechanisms by which modification by sputtering of TiO₂ and high temperature influence the insulation properties were analyzed. The results show that the surface discharge intensity increases with the increase in temperature, the modification by sputtering of TiO₂ can significantly inhibit the partial discharge of PTFE, and the flashover voltage first increases and then decreases with the increase in the modification time. The modification by magnetron sputtering can effectively increase the surface potential decay rate of the PTFE, increase the shallow trap energy density, effectively avoid charge accumulation, inhibit the partial discharge phenomenon, and improve the surface electrical insulation and anti-aging properties.

Ambient temperature has significant influence on properties of oil–paper insulation, which makes surface discharge process complex. This paper aims at revealing the influence mechanism of ambient temperature on surface charge and discharge behaviours under DC voltage. The oil–paper with thickness of 0.08 mm was used and the ambient temperature varies from 20 to 80°C in this paper. The results of surface potential decay (SPD) experiments show that the initial surface potential declines and the process of SPD is accelerated with increasing temperature because of higher carrier mobility. Additionally, both shallow and deep trap energy level become deeper, the shallow trap density is enlarged while the deep trap density is shrunken at higher temperature. The surface discharge tests were performed and Weibull results indicate that it is prone to occurring surface discharge at higher ambient temperature. The possibility of surface discharge under negative voltage is larger than that under positive voltage because of polarity effect. It is concluded that more carriers escape from deep traps to participate in the procedure of surface discharge at higher temperature, which declines the surface discharge voltage.

Nonuniform electric field distribution is one of the key issues for the superconducting cable terminals. This paper tries to modify the electric field distribution in the stress cone of HTS dc cable terminals by the nonlinear conductive epoxy/ZnO insulation, in-stead of the insulation with a fixed conductivity. The nonlinear conductivity of epoxy/ZnO composites is measured, and a finite element simulation model of the +100 kV HTS dc cable terminal is established to analyze the electric field distribution at the steady and transient state. The results show that the field-dependent conductivity has a great effect on the dc electric field distribution. If the nonlinear coefficient is excessively large, the electric field in the polypropylene laminated paper (PPLP) will be extremely strong; otherwise, the electric field in the terminal insulation will be extremely strong. The epoxy/ZnO composites with an appropriate nonlinear conductivity can effectively modi-fy the dc electric field distribution at the stress cone surface, es-pecially at the triple junction. As the impulse superimposed on the dc voltage is applied, the maximum field is always located in the PPLP layer. The nonlinear conductive epoxy/ZnO compo-sites could play an important role in promoting the development of stress cone of HTS dc cable terminals.

The current lead insulation of high-temperature superconductivity equipment is under the combined action of large temperature gradient field and strong electric field. Compared with a uniform temperature field, its electric field distortion is more serious, and it is easy to induce surface discharge to generate high-energy particles, destroy the insulation surface structure and accelerate insulation degradation. In this paper, the degradation reaction process of bisphenol F epoxy resin under the impact of high-energy particles, such as O₃⁻, HO^–, H₃O⁺ and NO⁺, is calculated based on ReaxFF simulation. According to the different types of high-energy particles under different voltage polarities, the micro-degradation mechanism, pyrolysis degree and pyrolysis products of epoxy resin are analyzed. The results show that in addition to the chemical reaction of high-energy particles with epoxy resin, their kinetic energy will also destroy the molecular structure of the material, causing the cross-linked epoxy resin to pyrolyze, and the impact of positive particles has a more obvious impact on the pyrolysis of epoxy resin.

Current lead is an important part of the superconducting cable termination. When a short circuit fault occurs, a large amount of heat generated in a short period of time will affect the tempera-ture distribution of current leads. In this paper, a temperature field simulation model of current leads is built on the basis of the-oretical calculation. Based on the optimized parameters of the HTS cable, the influence of magnitude and time of short circuit current on the temperature distribution of the current lead is studied, and the effect of the short circuit fault on temperature rise in different positions is also analyzed. The obtained results show that the magnitude and time of short circuit current have great effects on temperature distribution of current lead. Effect of short circuit current on the temperature distribution at the hot end is larger than that at the cold end.

The current lead insulation of the high temperature superconducting DC current limiter is in the terrible working environment of strong electric field and temperature gradient field from room temperature to liquid nitrogen (LN ₂ ) temperature. Bisphenol F epoxy resin, as a common terminal insulation material, is prone to surface flashover during equipment operation, which leads to premature failure of insulation. In order to improve the reliability of the terminal insulation system, epoxy resin/γ-Al ₂ O ₃ nanocomposites were prepared. The dielectric constant, DC conductivity, trap distribution, partial discharge characteristics and DC surface flashover voltage of the nanocomposites at room temperature and in LN ₂ were measured and analyzed. The results show that with the increase of γ-Al ₂ O ₃ nanoparticles content, the DC surface flashover voltage of the nanocomposites first increases and then decreases, and the partial discharge inception voltage generally increases. Appropriate γ-Al ₂ O ₃ nanoparticles doping can effectively inhibit the generation and development of surface discharge.