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 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.

Aiming to the copolymerized polypropylene (PP) material with low transparency, an electrical tree initiation voltage test system based on high frequency current sensor (HFCT) was designed. It was confirmed that the test system could detect partial discharge signal as low as 5 pC, and the test sensitivity was higher. Through the identification test of partial discharge signal, it was found that the main spectra of discharge caused by electrical tree initiation located at 12.9 MHz, which were different from the other disruptive partial discharge signals probably generated in test system. It was proved that the obtained partial discharge signal with a specific frequency characteristic was caused by the electrical tree initiation of sample. The transparent XLPE sample was conducted verification experiment, it was found that the electrical tree initiation voltage measured by the test system was almost the same as that measured by microscopic observation system, which confirmed the practicability of the electrical tree initiation voltage test system based on HFCT. Then, the effects of three voltage stabilizers of AOHBP, RBBT, and RQCT on the AC electrical tree initiation voltage of copolymerized PP material were investigated, respectively. The results show that three kinds of voltage stabilizers can all increase the initiation voltage and quenching voltage of partial discharge in the process of electrical tree initiation of PP with appropriate addition amounts. The optimal components are PP+0.6 phr AOHBP, PP+0.4 phr RBBT, and PP+0.6 phr RQCT, respectively. Among them, PP+0.6 phr AOHBP has the best inhibiting effect of electrical tree initiation, making the initial voltage of electrical tree increase by 33.0%.

In this paper, the positive and negative DC breakdown voltage of ester insulating oils and mineral insulating oil in extremely uneven field under small and medium gap were studied, and then compared with their lightning breakdown voltage. The results show that the DC breakdown voltage of ester liquids is lower than that of mineral insulating oil. The negative DC breakdown voltage is lower than the lightning breakdown voltage under small gaps, but it is higher than the lightning breakdown voltage under medium gaps.

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.

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.

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%.

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.

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.

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.