The boron nitride nanosheets (BNNS) was surface modified by γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560), and then epoxy resin/functionalized BNNS (EP/BNNS-KH560) composites were prepared by doping BNNS-KH560 into epoxy resin matrix. The structure and morphology of the functionalized BNNS were measured, and the properties of EP/BNNS-KH560 composites were studied. The results show that the surface of BNNS is grafted with KH560 successfully, which exhibits a transparent thin layer structure under transmission electron microscope. The addition of BNNS-KH560 with a wide energy level gap can maintain the high insulating properties, excellent dielectric properties, and mechanical properties of the composites, and improve their thermal stability. Additionally, the BNNS-KH560 can form a good heat conduction channel in epoxy resin matrix, and improve the thermal conductivity of the composites effectively. When the mass fraction of BNNS-KH560 in composites is 20%, the thermal conductivity of the composites can reach 0.51 W/(m·K).

The operating environment of EMU is complex, under the influences of multiple factors such as electricity, heat, and high-speed airflow, the performance of insulating material for high-voltage cable terminal on the roof is an important factor affecting the safety and stability of power supply system for EMU. In this study, the thermal conductivity, glass transition temperature, and dielectric properties of typical insulating materials for cable terminal on the roof were tested and analyzed by combining experimental analysis with simulation calculation. The electric field distribution at room temperature and the temperature distribution at different ambient temperatures of the cable terminal were studied by establishing an electric-thermal coupling simulation model of the roof cable terminal. The results show that the thermal conductivity of both ethylene-propylene-diene monomer (EPDM) and epoxy resin (EP) increases with the increase of temperature, and decreases with the increase of temperature when the temperature is higher than 80℃. At room temperature, the thermal conductivity of EPDM and EP is 0.251 W/(m·K) and 0.431 W/(m·K), respectively. The dielectric constant of EPDM decreases gradually with the increase of temperature, decreasing from 3.7 at -60℃ to 3.28 at 100℃. The dielectric constant of EP increases gradually with the increase of temperature, increasing from 5.02 at -60℃ to 5.29 at 100℃, which is due to the difference of their glass transition temperature. The simulation results show that the change of electric field at the terminal of AC cable caused by temperature is small, the maximum distortion point occurs at the root of stress cone, and the electric field is 3.12 kV/mm. The secondary electric field concentrates in the main insulation of cable, and the electric field is 2.9 kV/mm.

Electrical tree is a common type of insulation deterioration in power cables. The growth of electrical trees will change the performance of insulating materials, thereby threatening the safe operation of cables. However, traditional detection methods are often unable to realize effective detection of the tiny electrical trees deteriorated area in cable. A 10 kV single-core cross-linked polyethylene (XLPE) was selected, and electrical tree defects were introduced into its insulation. The insulation conductivity and equivalent capacitance between the inner and outer semiconducting layers at different growth stages of electrical trees were measured, and the electrical trees deteriorated area was tested and located by broadband impedance spectroscopy and inverse Fourier transform method. The results show that the growth of electrical trees increases the conduction current of the cable insulation significantly. The increase of electrical tree cumulative damage makes the capacitance value between the inner and outer semiconducting layers increase. Due to the change of conductivity and capacitance, the wave impedance of the electrical tree deteriorated area distorts. Using the broadband impedance spectroscopy and inverse Fourier transform methods can realize the accurate location of the electrical tree deteriorated area. At the same time, the different growth stages of electrical tree will significantly affect the amplitude of distortion points in the impedance spectroscopy and inverse Fourier transform spectrum.

The dry and cold environment of the Qinghai-Tibet Plateau is easy to make the insulators of railway catenary ice-coated, causing serious ice flash accidents. To study the operating status of ice-coated insulators in catenary, a two-dimensional ice-coated model of cantilever insulators was established according to the winter environmental characteristics of Golmud station on the Qinghai-Tibet railway, and the porcelain insulator XP-160 and composite insulator FXBW-110/100 were used as contrast. The spatial electric field distribution and surface temperature distribution characteristics of different types of ice-coated insulators were analyzed by electrostatic field and Joule heat field simulation. Finally, the shed structure of the insulator was optimized. The results show that as the thickness of ice layer and the length of ice crystal increase, the field intensity of each insulator increases gradually, and the surface temperature continues to rise. When the insulator is bridged by the ice crystal, the field intensity decreases, which is slightly lower than the field intensity of clean insulator. The increase of arrangement angle for the cantilever insulator will lead to the increase of electric field, but it has little effect on the temperature. Therefore, the arrangement angle of cantilever insulator should decrease during installation. The insulators with one large and two small shed structure can effectively reduce the increase of field intensity and suppress the temperature rise.

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.

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.

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.

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.

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.