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 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 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.

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.

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.

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.

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.

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.

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.

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.