Aiming at the contaminant composition of transmission line insulator in Ningxia Yellow River irrigation area are not clear, and the degree of environmental impact is unknown, we subdivided the environment of Ningxia Yellow River irrigation area into 5 categories: industry, agriculture, urban residential area, desert, and grassland, and insulator contaminants samples in the corresponding environments were taken to conduct microscopic morphology, element content, crystal composition, anion and cation composition and content detection and analysis. Meanwhile, the pollution accumulation characteristics of insulators in irrigated and non-irrigated areas were compared and analyzed. The results show that the soil composition in the Yellow River irrigation area determines the basic composition of insulator contaminants. The industrial and agricultural environment have bigger influence on the micro-structure and different ingredients content of the insulator contaminants, and the urban residential area is followed. The pollution accumulation degree of insulators in irrigated areas was obviously higher than that in non-irrigated areas. In order to further improve the operation reliability of the transmission lines in Ningxia Yellow River irrigation area, some suggestions for anti-pollution flashover operation and maintenance are put forward, which can be use as reference for relate operation and maintenance units.

Dibenzyl disulfide (DBDS) is a corrosive impurity in transformer oil, which can easily lead to transformer failure. In this paper, a γ-Al₂O₃ was prepared from pseudo-boehmite by calcination method, and a series of Ag/γ-Al₂O₃ were prepared by loading Ag⁺ on γ-Al₂O₃ carrier by equal volume impregnation method. The adsorption phase equilibrium and kinetics curves of dibenzyl disulfide on Ag/γ-Al₂O₃ and the removal rate of dibenzyl disulfide in operating transformer oil by Ag/γ-Al₂O₃ were studied. The results show that the adsorption isotherm of DBDS on Ag/γ-Al₂O₃ belongs to Langmuir model. The equilibrium adsorption capacity of Ag/γ-Al₂O₃ for DBDS is 69.5 mg/g at 298 K, which is 105.9 times higher than that of γ-Al₂O₃, showing excellent adsorption performance. The removal rate of Ag/γ-Al₂O₃ for DBDS in the operating transformer oil is close to 100% under appropriate mass ratio of oil and adsorbent, and the DBDS adsorption capacity of Ag/γ-Al₂O₃ is not affected by temperature changes. The adsorption kinetic process of DBDS on Ag/γ-Al₂O₃ is well fitted by the pseudo-second-order kinetics model, and the activation energy of DBDS desorbing from Ag/γ-Al₂O₃ is 71.673 kJ/mol.

In order to compare the thermal ageing properties and application characteristics of polyamide fiber paper commonly used for wire wrapping in the market, the thermal ageing properties in air, metal, and oil, oil absorption properties, and oil pollution properties of 2 mil aramid paper for wire wrapping from home and abroad were studied. The results show that the thermal ageing properties of three kinds of meta aramid paper in air are basically at the same level. When the aramid paper contacts with metal, the thermal ageing properties of the domestic aramid paper (2^#) is significantly lower than that of foreign aramid paper (1^#) and ZhuZhou Times Fiber Pioneer aramid paper (3^#), the gap with the latter two is at least 15%, and the performance retention rates of the latter two are basically the same. After the aramid paper conducts thermal ageing in mineral oil (105℃), synthetic ester oil (130℃), and silicone oil (150℃) for 168, 336, and 504 h, respectively, the properties of three kinds of aramid paper do not decrease significantly. After the aramid paper is immersed in insulating oil, the oil absorption characteristics of three kinds of aramid paper are close, and there is no obvious pollution to oil, which indicates that the aramid paper has good compatibility with insulating oil. The research shows that the comprehensive performance of 3^# aramid paper is better than that of 2^# aramid paper, which indicates that 3^# aramid paper can realize the domestic substitution of high level aramid insulating paper.

The application status of polypropylene (PP) cables were introduced in this paper, and the modification principles, existing advantages and disadvantages, and research status of polypropylene insulation materials were summarized. The research and development emphasis of polypropylene semi-conductive shielding materials were described. Finally, the research progress of PP cable at home and abroad was introduced, and the research direction of PP material was pointed out.

In order to study the performance changes of irradiation crosslinking low-smoke halogen-free flame-retardant insulation layer and sheath layer for photovoltaic cables before and after getting moistened, the insulation layer and sheath layer of photovoltaic cable with various water-immersion time were conducted mechanical properties, thermal extensibility, dynamic thermomechanical analysis (DMA), Fourier transform infrared spectroscopy (FTIR), and volume resistivity tests. The results show that the long-term water-immersion causes hydrolysis of molecular chains in the material, and the entanglement of molecular chains weakens, which lead to decrease of tensile properties of samples. After water-immersion, the initial storage modulus of the insulation layer and sheath layer samples decreases, the adhesion force between filler particles and matrix resin decreases, and the mechanical loss peak of the insulation layer presents double peaks characteristic. With the increase of moistening degree, the EVA in the polyolefin matrix swells, and the free volume increases. Some flame retardant fillers are separate from the binding of matrix and become impurity ions, making the carrier concentration and mobility increase, which leads to continuous decrease of volume resistivity.

Electrical tree is a common phenomenon in XLPE cable, and there may be different scales of spike defects during the operation of cables. In this paper, the relationship between electrical tree growth morphology and partial discharge characteristics under different tip curvature radius was studied. The results show that the sample with small tip curvature radius will eventually develop into branch electrical tree under the tree initiation voltage, while the sample with large curvature radius will eventually develop into cluster electrical tree, and the discharge capacity of cluster electrical tree is greater than that of branch electrical tree. The positive and negative half cycle of PRPD diagram of the cluster electrical tree is similar to the “wing shape”. The discharge shape of the positive half cycle of the branch electrical tree is “triangle shape”, and the negative half cycle shape is “wing shape”. The growth rate of the two electrical trees shows the characteristics of “fast-slow-fast”. The growth rate of the branch electrical tree is higher than that of the cluster electrical tree, and the branch electrical tree is more harmful in the actual cable.

In DC transmission lines, cable line is easy subjected to the impact of operating overvoltage and lightning overvoltage, which leads to cable line superimposed by impulse voltage on the basis of DC voltage, making the space charge accumulation on insulation layer change. In order to study the effect of impulse voltage superposition on the charge accumulation in the operating DC cable lines, a PEA method space charge measurement system under DC superimposed impulse voltage was developed through improvement on the traditional PEA method, combining with equivalent circuit formula deduction and Pspice software simulation, and reasonable selection of RC-component in measurement system. The space charge characteristics of XLPE samples under DC superimposed impulse voltage were measured. The results show that the coupling efficiency of impulse voltage and DC voltage is very high, and the space charge characteristics show that the superimposing the same polarity of impulse voltage can promote the injection and migration of the same polarity charge more compared with superimposing different polarity of impulse voltage.

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).

Composite insulators have been widely used in power transmission lines. In recent years, there are many grid accidents caused by insulator core rod deterioration. It is urgent to find out the influence factors and rules of composite insulator core rod deterioration. In order to study the influences of different voltage applied time and environmental humidity on the core rod deterioration of composite insulator under uniform electric field, the electric field distribution generated by the dielectric barrier discharge method was simulated and analyzed. An electrical ageing experiment platform was designed and built, and the core rod samples were conducted 200 h, 400 h, and 800 h of electrical ageing tests at power frequency under dry and humid environments. The physical and chemical properties of new sample and the aged samples were tested, and the corresponding influence laws were analyzed. The results show that after electrical ageing, the epoxy resin content in the core rod decreases. When the ageing time is less than 400 h, the epoxy resin content under humid and dry environments has little difference. When the ageing time increases to 800 h, the epoxy resin content under humid environment is significantly lower than that under dry environment.

In order to evaluate the impregnating resin for driving motor of new energy vehicles, epoxy resin and polyester imide resin were selected as research objects. The properties of the two impregnating resins were compared by thermal weight loss and bonding strength tests, and their long-term ageing characteristics were compared emphatically. The results show that the VOC content and long-term thermal resistance of the two impregnating resins meet the requirements. The bonding strength of epoxy resin is higher than that of polyester imide at 25℃, but decreases rapidly at 150℃ and 180℃. Ageing at 200℃ for 2 000 h, high and low temperature impact for 600 cycles, high and low temperature for 8 cycles under ATF oil immersion, high and low temperature for 8 cycles under ATF oil + 0.5% water closed immersion, and ageing at 150℃ for 2 000 h under ATF oil immersion experiments have similar effects on the bonding strength of the two impregnating resins. However, under the condition of ATF oil + 0.5% water closed immersion at 150℃, the bonding strength of epoxy resin is only 16.41%, 13.64%, 4.29%, and 4.29% of the initial value after aged for 500, 1 000, 1 500, and 2 000 h, while the bonding strength of polyester imide is higher than the initial value under the same condition. The structural and elemental changes of epoxy resin before and after its bonding strength decreasing significantly were compared by Fourier transform infrared spectroscopy and X-ray electron spectroscopy, it is inferred that the hydrolysis at high temperature is the main reason for the decline of bonding strength.