The research progresses of different polymers (polyimide, perfluorocyclobutyl-based polymer, benzoxazinyl polymer, benzocyclobutene resin, etc.) with low dielectric constant and low dielectric loss factor in recent five years were reviewed. The influence of different design strategies of polymer structures (chemical composition, molecular structure, pore structure, etc.) on their properties (dielectric properties, water absorption, thermal stability, mechanical properties, etc.) was discussed mainly, and the influencing mechanisms were analyzed briefly. At last, the four common methods (reducing molecular polarity, increasing the free volume of molecular, introducing porous structure, and introducing cross-linking structures) for the design of different low dielectric polymers were summarized, and the development direction of low dielectric polymers in future was prospected.

In order to study the rejuvenating effect difference of rejuvenation fluid on water tree ageing cable when different catalysts were combined with siloxane, we selected a methyl phenyl dimethoxy siloxane (PMDMS) and a long-chain siloxane, tetraisopropyl titanate (TIPT) and long-chain benzene sulfonic acid two catalysts to prepare four rejuvenation fluids with different formula. Water tree aged cables were rejuvenated by injecting the rejuvenation fluid and conducted second ageing, and their electrical properties and microstructure changes were analyzed by the power frequency breakdown test, water tree morphology observation, and FTIR test. The results show that four kinds of rejuvenation fluids can inhibit the growth of water tree, and the breakdown voltage of the water tree aged sample is improved. The rejuvenation fluid composed of long-chain siloxane and long-chain benzene sulfonic acid has the highest retention rate in the insulation layer, and the rejuvenating effect is the best. The rejuvenation fluid composed of PMDMS and long-chain benzene sulfonic acid has the lowest retention rate in the insulation layer, and the rejuvenating effect is the worst. It is proved that when the diffusion speed of siloxane and catalyst in insulation layer matches, the retention rate of the siloxane can be improved, and the long-term rejuvenating effect can be enhanced.

In this paper, the research process of alicyclic polyimides (Al-PIs) at home and abroad in recent years was reviewed, and the synthesis of typical monomers and polymers were described from the historical evolution perspective mainly. The applications of alicyclic polyimides in transparent flexible display, gas separation membrane, photosensitive material, and liquid crystal orientation membrane were discussed, and the development trend and application prospect of alicyclic polyimides were prospected.

The free acid value and PH₃ release amount of PA66 prepared by red phosphorus flame-retardant with different coating process were compared, and the morphology and contact resistance of the corresponding contact element after surface contamination were tested. The effects of housing using different red phosphorus flame-retardant PA66 on the electrical performance of AC contactor were analyzed, and the experiment of simulating the actual application environment was conducted. The results show that the red phosphorus flame-retardant PA66 using multi-layer coating process has low free acid value and PH₃ release amount, which has little effect on the electrical performance of AC contactors and can be used as one of the alternative materials for AC contactor housing.

Three kinds of organic ultraviolet absorbers with the same concentration were added to polyethylene terephthalate (PET) films, and the properties of PET films before and after UV ageing were tested, and then the effects of ultraviolet absorbers on the UV ageing properties of PET films were studied. The results show that the UV ageing properties of PET films are related to the structure of ultraviolet absorber. Compared with triazine and benzotriazole ultraviolet absorbers, oxazinone ultraviolet absorber exhibits red shift of UV absorption wavelength, wider UV absorption range, and stronger UV absorption intensity because of its hyperconjugated structure. With the increase of ultraviolet radiation energy, the mechanical properties and glossiness of the three kinds of UV resistant transparent films decrease gradually, and the yellow index increases gradually. When the ultraviolet radiation energy is higher than 120 kWh/m², the property differences of the three kinds of UV resistant transparent films before and after ageing are obvious. The property difference of the film containing oxazinone hyperconjugated structure ultraviolet absorber before and after UV ageing is the smallest, and the ageing resistance is the best.

The setting of boundary conditions is a key factor that affects the accuracy of stress calculation for basin insulator. In this paper, an axisymmetric model of basin insulator for miniaturized 252 kV GIS was established. The Mooney-Rivlin function model of rubber sealing ring was introduced to simulate and calculate the stress of basin insulator under different constraint boundary conditions by finite element analysis software, and the result was compared with the measured value of hydraulic test. The results show that the boundary condition using the friction contact is consistent with the engineering practice, which is suitable for the setting of stress simulation boundary condition for basin insulator. The research results can provide reference for the miniaturization and lightweight design of basin insulator of other voltage levels.

The dielectric constant (D_k) and dielectric loss factor (D_f) of polyimide under high frequency can be reduced by changing the polarity of polymer and introducing pore structure in summary. In this paper, the research progress of the two modification methods at home and abroad in recent years was summarized. It is indicated that the properties of polyimide can be optimized by adding pore structure on the basis of introducing polar macromolecules. At the same time, the shortcomings of properties characterization in literature were pointed out, and the suggestions were proposed.

The linear expansion coefficient of cured E51 epoxy resin was tested by using the TMA mode of DMA, and the effects of curing agent types (methyltetrahydrophthalic anhydride (MeTHPA), 4,4-diaminodiphenylmethane (DDM), dicyandiamide (dicy)), and filler powder types and dosage on its linear expansion coefficient were analyzed. The results show that when T<T_g, the linear expansion coefficient of cured E51/Dicy is smaller than that of cured E51/MeTHPA and E51/DDM. When T＞T_g, the linear expansion coefficient of cured E51/dicy is larger than that of cured E51/MeTHPA and E51/DDM. After filling SiO₂, Al(OH)₃, and Al₂O₃ respectively, the linear expansion coefficient of the epoxy composites are significantly lower than that of pure epoxy material, and the linear expansion coefficients of the epoxy composite filled with Al₂O₃ is the smallest. With the increase of inorganic filler content, the linear expansion coefficient of the epoxy composite decreases. However, when the mass fraction of inorganic fillers is 70%–80%, the linear expansion coefficient changes little with the change of filler content.

In order to study the influence of temperature on the nonlinear resistance characteristics of different stress grading materials, a measurement method using the presetting low resistivity tape as the electrode was proposed and applied. The nonlinear volt-ampere characteristics of four stress grading materials under different temperatures were tested. At the same time, the influencing degree of temperature on the nonlinear resistance characteristics of different stress grading materials were studied by function fitting method. The distribution differences of surface electric field along the stress grading structure at stator winding end of 24 kV hydro-generator under the withstand voltage test voltage and the rated phase voltage at different temperatures were further simulated and compared. The results show that the nonlinear volt-ampere characteristics and surface resistivity of four stress grading materials show obvious temperature dependence, with the increase of temperature, both the initial surface resistivity and nonlinear coefficient decrease, there is little difference among the surface electric field distributions along the stress grading structure of 24 kV hydro-generator under different temperatures.

A aluminum thin-walled cylinder was used to replace the cable to finish the actual setting process of terminal. The interface pressure between the 110 kV prefabricated cable terminal and the stress cone was measured by the electrical measurement method and elastic mechanics theory. By finite element simulation analysis and comparing the calculating result and test result, a reasonable finite element simulation analysis model was established and the terminal setting process was simulated. Several analysis models with different interference were established to study the influence of interference, silicone rubber material parameter, and spring compression on the interface pressure. The results show that the maximum interface pressure is located in the middle of the maximum radius of stress cone. The interface pressure is proportional to the spring compression before the spring compressing to 90 mm, and the interface pressure changes little during the process of the spring compressing from 90 mm to 85 mm. The interfacial pressure is affected by the interference and the cross-sectional area of cable, and it is greatly affected by the elastic modulus of stress cone, and less affected by the elastic modulus of cross-linked polyethylene (XLPE) insulation.