At present, most of the researches on SF₆ substitute gas rely on experimental selection, with high cost, heavy workload, and low efficiency. Studying the theoretical relationship between molecular structure parameters and insulation performance of SF₆ can provide direction for the molecular design and selection of SF₆ substitute gas, and improve the researching efficiency. Firstly, we focused on the current quantitative structure-activity relationship model with development potential, especially a new type model involving molecular electrical parameters, force parameters, and geometric parameters. Then the molecular design method based on the new quantitative structure-activity relationship model was introduced. Finally, the problems and development directions to be further studied of the new quantitative structure-activity relationship model in the research of SF₆ substitute gases were discussed from the three aspects of gas insulation performance database, the diversification of predictive properties, and the improvement of molecular design methods.

In order to research the insulation ageing characteristics of cross-linked polyethylene (XLPE) cables, it is necessary to perform ageing tests under laboratory conditions. In this paper, the current research progress on insulation ageing tests and detection techniques of XLPE cables was reviewed. Firstly, the common ageing types and phenomena of XLPE cables were introduced, and the current research results on the growth mechanism and influencing factors of water tree ageing and electrical tree ageing were elaborated. Secondly, the accelerated ageing test methods for XLPE cables under laboratory conditions and their effect on cables were introduced. Then, the current detection methods of cable insulation ageing were briefly classified, the principle, applicable conditions, and advantages and disadvantages of each methods and the characteristics and application method of each insulation detection stage were introduced. Finally, the problems related to cable insulation ageing and their future research directions were discussed.

In this paper, five kinds of epoxy resin samples with different ratios of acid anhydride curing agent were prepared by hot pressing method. The thermal and dielectric properties of the samples were tested, and then the best anhydride curing agent ratios were selected, and the steric effects caused by methyl substitution were analyzed. The results show that the mixed anhydride curing sample with the molar ratio of methylhexahydrophthalic anhydride and hexahydrophthalic anhydride of 8∶2 shows the highest glass transition temperature, and the electrical strength is improved, while the dielectric loss remains unchanged, which is closely related to the increased rigidity of the system.

The liquid crystal epoxy monomer was cured to obtain liquid crystal epoxy resin prepolymer, and liquid crystal epoxy resin fiber films with different fiber diameters were obtained by electrospinning technique. The birefringence of the samples was observed by polarizing microscopy and removable hot stage, and the mechanical properties, dielectric properties, and insulation properties of the liquid crystal epoxy resin fiber films with different fiber diameters were systematically evaluated. The results show that the liquid crystal epoxy resin prepared by electrospinning method can form and maintain an ordered liquid crystal phase. The finer the fiber diameter, the higher the degree of orientation arrangement, and when the fiber diameter is 280 nm, the tensile strength (7.53 MPa) of the liquid crystal epoxy resin fiber film is the largest. Under the test frequency ranging from 10^-1 Hz to 10⁶ Hz, the dielectric constant of the liquid crystal epoxy resin reaches to the highest value of 2.34, and the dissipation factor is only 0.002 at industrial frequency. In addition, the liquid crystal epoxy resin fiber film has high resistivity, and when the fiber diameter is 280 nm, the volume resistivity of the liquid crystal epoxy resin fiber film can reach to 5.49×10¹⁵ Ω·cm.

This article introduced the relevant characteristics of fungi. Fungi were cultivated under laboratory conditions and transplanted to the surface of silicone rubber insulators. Then, the static contact angle, ESDD, NSDD, and pollution flashover voltage of contaminated silicone rubber insulators were measured. The inhibition of fungi on the hydrophobicity of silicone rubber insulators and its influence on the pollution flashover voltage were analyzed. The results show that the adhesion of fungi on the surface of the silicone rubber insulator decreases the hydrophobicity of the insulator. The higher the concentration of fungus, the worse the hydrophobicity; the pollution flashover voltage on the surface of the silicone rubber insulator decreases slightly due to the adhesion of fungi; at the same time, the higher the concentration of fungi, the higher the ESDD and NSDD.

Combined with the special application environment and special structural characteristics of traction motor, the polyester imide insulation system of traction motor based on polyesterimide resin and three-in-one mica tape was studied in this paper. The heat resistance and processability of polyesterimide resin were studied by thermogravimetric analysis (TGA) and viscosity-temperature curve, on the basis of it, simulated insulation structure was prepared using the three-in-one mica tape with good compatibility with polyesterimide resin to verify the electrical ageing performance and reliability of the insulation system. The results show that the insulation system based on the selected polyesterimide resin and three-in-one mica tape has outstanding processability, mechanical properties, electrical properties, heat resistance, reliability, and low cost. The heat resistance index reaches to 215, which meets the requirements of high bonding strength, high heat resistance, and high reliability of traction motor.

Vegetable insulating oil is a kind of environment-friendly insulating oil with high ignition point, its electrical performance is similar with that of mineral insulating oil, but the kinematic viscosity is higher than that of mineral insulating oil. In this paper, the process conditions for preparing insulating oil with low viscosity by transesterification reaction using vegetable insulating oil as raw material and NaOH and ethanol as catalyst were discussed. And the effect of transesterification reaction conditions on the kinematic viscosity of vegetable insulating oil was investigated. The results show that when the molar ratio of alcohol to oil is 6∶1, the reaction time is 1h, the reaction temperature is 70℃, and the mass fraction of NaOH is 0.5%, the kinematic viscosity of the product can reach to 5.81 mm²/s, which is close to that of mineral oil. When the mass fraction of catalyst is no more than 0.5%, the kinematic viscosity of the product is inversely proportional to the amount of catalyst, and vegetable insulating oils with different kinematic viscosity can be prepared by controlling the amount of catalyst.

In this paper, the compatibility of four kinds of insulation materials, including enamelled round wire, enamelled rectangular wire, impregnated resin, and rubber gasket materials, with automatic transmission fluid (ATF) for oil-cooled electric vehicle motor was studied. Deionized water was added to ATF and the volume fraction was 0.5%, the compatibility experiments of four insulation materials with ATF were conducted at 155℃ according to the thermal class. The results show that the enamelled round wire, enamelled rectangular wire, and the impregnated resin has good compatibility with ATF. The performance of acrylic rubber was degraded obviously during the experiment, which does not meet the performance requirements of sealing materials.

In order to explore the impact of the performance of silicone dry mica tape on the reliability of insulation system of traction motor, we conducted the material basic performance, laboratory simulation of wire rod, and insulation system reliability evaluation on two imported mica tapes and two domestic mica tapes. The results show that the mica tape with less resin and higher air permeability shows a better compatibility with the silicone impregnating varnish. The formed insulation system has a lower thermal dielectric loss factor and a higher curing rate, which improves the breakdown voltage and improves the reliability of the insulation system.

In order to obtain superhydrophobic film by simple and mold free method, on the basis of the transformation of 3D printer transmission system, we filled hydrophobic silica nanoparticles in thermoplastic elastomer solution material to prepare printing ink. Then ordered porous superhydrophobic film was prepared using the ink by 3D printing technology. The printability of ink and the wettability, wear resistance, insulating property, and oil-water separation of the film were investigated. The results show that the porous structure film prepared by this method shows well super-hydrophobicity, high oil-water separation efficiency, good insulating property and mechanical properties such as wear resistance and durability.

The surface flashover of insulating material is affected by many factors, such as surface roughness, nano fillers, and chemical functional groups. In this study, polyamide mesh was used as support and hydrophobic nano silica particles were used as modified materials. Nano fillers were embedded into polyamide mesh by the treatment method of dissolution and resolidification. The microstructure was determined by changing the mesh size, and the chemical groups on the composite surface were changed by fluorinated nanoparticles. The coupling effect of microstructure/nano filler on surface flashover was studied, and the material was endowed with superhydrophobic properties. The results show that with the polyamide mesh of 300 mesh, the composite has the best anti flashover performance, and the flashover voltage was increased by 20%.

The corona accelerated ageing was conducted on silicone rubber, the insulation characteristic parameters of silicone rubber under different ageing time were measured, and the ageing mechanism of silicone rubber was deeply discussed according to the parameters. The results show that corona ageing causes serious damage to the surface structure of silicone rubber, and obvious holes and cracks are formed on its surface, resulting in serious pulverization. Corona ageing makes the long molecular chain of silicone rubber break into small molecular chain, reduces the flexibility of silicone rubber molecular chain, forms various defects, which leads to the decrease of the insulation performance of silicone rubber. With the increase of corona ageing time, the energy level centers of electron and hole traps decrease slowly at first and then decrease fast. Corona ageing leads to the gradual development of deep traps into shallow traps, reduces the binding effect on electrons, and finally leads to the occurrence of surface flashover of silicone rubber.

Outdoor oil-filled cable terminals are key accessories in high-voltage transmission and transformation lines. However, high-voltage cable terminal failures have occurred continuously under cold weather in China, which seriously affects the safety of power grid operation. For this reason, an equivalent experimental device for the cable main insulation-stress cone interface insulation of the oil-filled cable terminal was designed, and the effect of the silicone rubber/XLPE interface coating silicone oil on the partial discharge activity under 10℃ and -30℃ was tested. Moreover, the failure mechanism was studied according to microscopic observations and electric field simulation. The results show that under 10℃, coating silicone oil on the interface can effectively improve the compatibility and insulation strength of the cable terminal interface. When there is no scratch, the partial discharge initial voltage of the interface coating with silicone oil is about 17.2% and 200% higher than that without coating silicone oil. However, under -30℃, silicone oil has a solidification shrinkage effect, resulting in the generation of air gap or the re-exposure of inherent blemish, and the partial discharge initial voltage decreases significantly, which is even slightly lower than that without coating silicone oil. The electric field simulation results show that the maximum field strength distortion value under very cold environment is 6.26 kV/mm, which is higher than the electric strength of air, and it is easy to cause discharge breakdown.

Accelerated thermal ageing test was conducted on mineral oil-paper, natural ester-paper, mineral oil, and natural ester at 140℃ for 1 640 h. The change law of acid value and dielectric dissipation factor of the four oil samples in different ageing stage were emphatically analyzed, and the appearance changes of aged oil and paper were compared. According to that, the influence of the participation of insulating paper on the properties of different insulating oils during the ageing process was comprehensively compared. The results show that the acid value, dielectric dissipation factor, and ageing degree of the aged oil samples without insulating paper are higher than those with insulating paper. The ageing difference of natural esters with and without insulating paper is smaller than that of mineral oil, and the holding capacity for acidic substances is better than that of mineral oil, which can delay the ageing of insulating paper to a certain extent.

In order to supply more accurate input voltage to the design of insulation structure for variable frequency wind generator, we took the stator winding of permanent magnet synchronous wind generator as the research object, the equivalent circuit model of cable and motor stator winding coil was built by MATLAB software, and the effects of cable length and the pulse width modulation (PWM) pulse rising edge time output by frequency converter on the transient voltage distribution characteristics of motor winding were analyzed. The results show that with the increase of cable length and the decrease of pulse rising edge time, the maximum voltage to ground and inter turn of motor end and winding increases, and the maximum voltage to ground transfers from the middle coil to the first coil. When the pulse rising edge time is 2.0 µs, the voltage distribution in the winding tends to be uniform.

Under repetitive impulse voltage, tests of the growth characteristics of electrical tree were conducted on laminar composite insulation consist of impregnating resin and insulating tape for wind turbine generator. The effect of impulse voltage repetitive rates on the electrical tree initiation characteristics, morphological features, and growth curve of the insulation composited by epoxy modified unsaturated polyester resin with polyimide film reinforced mica tape was studied. The growth characteristics of electrical tree extending feature along the interface of insulating tape was analyzed. The results show that under the bipolar square wave impulse voltage with the peak voltage of 7 kV and the repetitive rates of 500 Hz, 1 000 Hz and 2 000 Hz, respectively, the electrical trees in samples are all branch-shaped and the branches are relatively sparse. The electrical tree extends laterally along the interface when it grows to the insulating tape, hindering the radial growth of the electrical tree, increasing the breakdown time of the sample.With the increase of the repetitive rate of the impulse, the initiation time of the electrical tree is shortened, the initiation rate is promoted, the branches increases and its discharge channels becomes thinner, the fractal dimension is almost unchanged, and the average radial growth rate increases.

The high frequency repetitive impulse generated by the inverter can lead to uneven overvoltage with high amplitude along the stator windings, which will accelerate the ageing of insulation system and even cause faults. On the basis of the transient analysis software PSCAD/EMTDC, the equivalent circuit model for three-phase stator windings of 2.5 MW permanent magnet direct-drive generator was established, and the parameters of corresponding equivalent circuit were calculated by finite element method. Moreover, the experimental platform was built for verifying the validity of the calculation results. The results show that under the effect of three-phase pulse width modulation (PWM) pulse voltage, the amplitudes of the overvoltage to ground, coil to coil overvoltage, and turn to turn overvoltage of the stator winding for permanent magnet direct-drive wind generator show a decreasing trend from the connecting terminal of motor to the neutral point of winding. The experimental results further verify the accuracy of the equivalent circuit model of three-phase stator winding.

Aiming at the problerm of seleting energy in the intrinsic conductivity measurement by charge decay method,the intrinsic conductivity of polyimide was measured by charge decay method under the electron irradiation energy range from 5 keV to 20 keV. The influence of irradiated electron energy on the test results was studied, and the fitted method of surface potential decay data was improved by adding a polarization decay time constant. The results show that a higher irradiated electron energy causes a higher charged balance potential on the surface of insulating material, resulting in more serious polarization inside the dielectric, which affects the test results of the conductivity in charge decay method. The surface potential decay data can be fitted and interpreted well by the improved method, which provides an basis for the selection of irradiated electron energy.