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.

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 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%.

In order to achieve long-term stable extrusion of insulating materials, a cross-linked polyethylene with different antioxidant content was prepared by melt blending, and the effect of different antioxidant content on the scorch resistance of cross-linked polyethylene was studied. At the same time, the mechanical properties, electric strength, dielectric properties, and thermal properties of cross-linked polyethylene were comprehensively evaluated. The results show that with the increase of antioxidant content, the torque of cross-linked polyethylene decreases gradually, the cross-link time increases slowly, and the scorch resistance of the material is improved. In addition, the temperature of cross-linked polyethylene material is reduced slightly, which ensures the stability of long-term extrusion for material. The conductivity of cross-linked polyethylene does not change significantly with the increase of antioxidant content, while the AC electric strength and dielectric loss increase slightly. The AC electric strength increases by 4.5%, the dielectric loss factor is less than 5.0×10^-4, and the melting and crystallization characteristics do not change significantly.

High performance glass fiber reinforced epoxy resin composites were prepared by vacuum impregnation and autoclave molding using multifuctional AG80 epoxy resin and phenolic epoxy resin as composite epoxy resin matrix, composite diaminodiphenyl sulfone (DDS) as curing agent and 2-ethyl-4-methylimidazole as accelerator. The results show that the prepared high performance epoxy resin composites have excellent high temperature and high humidity resistance. When the content of DDS is 35 phr, the tensile strength, compressive strength, and bending strength of epoxy resin composites reach 385, 549 and 407 MPa at room temperature, respectively, the insulation resistance reaches 1.0×10⁹ Ω, and the bending strength reaches 210 MPa at 200℃. In addition, the epoxy resin composite still maintains good mechanical properties and insulating properties after high temperature and high pressure hygrothermal test at 205℃ and 140 MPa, which can meet the application requirements of petroleum logging tools in high temperature and high humidity environment.

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 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.

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.

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 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.