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.

The faults caused by internal interface defects of composite insulators is a great threat to the safe and stable operation of power grid. In order to study the influence of different shapes of defects and their sizes and moisture immersion on the electric field distribution of insulators, an isosceles triangle defect model including tip curvature radius parameter was proposed. A 3D model of 500 kV composite insulator was established, and the electric field of defects with different shapes and sizes and moisture ratio were simulated and compared by the COMSOL. The results show that the isosceles triangle defect model can better reflect the tendency of defect developing to the low voltage side. The tip curvature radius of defect has no obvious effect on the air gap, but there is a point effect in the water gap. With the increase of moisture content in the defect, the maximum electric field strength increases gradually. Under the action of point effect and moisture immersion, the electric field strength at the tip of low voltage side is distorted severely, which increases the possibility of partial discharge and accelerates its development to the low voltage side.

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.

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.

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.

From the perspective of inorganic nanoparticles hybrid polyimide (PI), the research status of dielectric constant, conductivity, electric strength, and corona resistance of PI hybrid materials at home and abroad in recent years was reviewed and commented. The influence of different inorganic nanoparticles doping on the electrical properties of PI materials was expounded, the problems existing in the process of PI hybrid were analyzed, and the direction of PI hybrid materials can be further studied was prospected.

Using aramid fibrid as reinforcing material and introducing into mica paper-based materials, we manufacture an aramid fibrid/mica composite insulating paper by wet paper with pulp. The morphology, mechanical strength, insulating properties, thermal stability, and glue permeability of the composite paper were systematically studied. The results show that the flake mica and ribbon-like aramid fibrid are orderly stacked to form a “brick-mud” structure. The increase of aramid content makes the composite paper structure more compact, and the mechanical strength also increases. With the increase of aramid content, the gap between mica is filled, and the air permeability of composite paper decreases. The electric strength and thermal stability of the composite paper decrease with the increase of thickness, but the composite paper still maintains good insulating properties and thermal resistance.

In order to improve the comprehensive performance of bisphenol A epoxy resin (DGEBA), bisphenol A epoxy resin was modified by alicyclic epoxy resin through blending, and the thermal, mechanical and electrical properties of the blending system were comprehensively analyzed. The results show that when the mass fraction of alicyclic epoxy resin 2021P is 10%, the blending system have better thermal, mechanical and electrical properties. Compared with the pure bisphenol A epoxy resin, the glass transition temperature of the blending system increases by 3.18%, and the bending strength and tensile strength increase by 3.95% and 4.65%, respectively. The leakage current decreases by 6.03%, the dielectric loss factor decreases by 24.25%, and the power frequency electric strength increases by 7.16%.

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 this paper, the aggregation morphology of copper products in transformer oil and its influence on the ageing performance of transformer oil were investigated. The aggregation morphology of copper products in oil were tested by molecular weight distribution test method, and the ageing properties of oil samples were also analyzed periodically. The results show that the distribution of copper products changes with the ageing time obviously. The proportion of ionic copper decreases gradually with the ageing time, while the proportion of colloidal and suspended copper exhibit a tendency of continuous accumulation. The acid value and dielectric loss factor of the transformer oil increase significantly with ageing time, while the breakdown voltage decreases continuously. The concentration of ionic, colloidal, and suspended copper are positively correlated with the acid value and dielectric loss factor, and negatively correlated with the breakdown voltage.