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.