In order to study the influence of the relative dielectric constant of motor insulation structure on the electric field distribution at different frequencies, this article took the relative dielectric constant of a main insulation structure at different frequencies as a variable to calculate its influence on the electric field distribution of the main insulation sandwich structure in the slot and the notch. At the same time, the optimization measures for the electric field of slot were analyzed. The results show that in the sandwich structure of main insulaton, because the film has a lower dielectric constant, it bears a larger electric field than mica tape. When the relative dielectric constant of the air at the notch is constant, the electric field strength of the air at the notch decreases slightly with the decrease of the relative dielectric constant of the main insulation. The insulating paint in the small gap at the chamfer of the notch iron core can reduce the electric field strength of air; without insulatin paint, the small gap generated by chamfer can produce a larger electric field strength of air. Vacuum potting of the notch can effectively reduce the electric field strength of air at the notch.

With the rapid development of microelectronics industry, flexible printed circuit board (FPCB) has proposed higher requirements on the dielectric properties of polyimide (PI) films, which is the interlayer insulating materialof FPCB. The conventional PI film cannot meet the requirements of 5G high-frequency communication because of its high dielectric constant. In this paper, the research progress of PI film materials with low dielectric constant in recent years were reviewed from two aspects of changing the intrinsic structure of PI and introducing porous structure, and the development prospect of low dielectric constant PI film materials were proposed.

The existing test method standards of the compatibility between electrical insulating fluids and structural materials at home and abroad were introduced, and the test method standards of the compatibility between electrical insulating fluids and structural materials in transformers, power capacitors, cable terminals, and oil cooling motors were discussed respectively. The similarities and differences of test conditions and evaluation parameters in each standard were summarized, and the shortcomings of current standards were analyzed. At last, the standard proposal of IEC 63177 Test methods for compatibility of construction materials with electrical insulating liquids proposed by Guangzhou Power Supply Bureau of Guangdong Power Grid Co., Ltd. was introduced compendiously, which will address the shortcomings of existing compatibility test methods.

In this paper, the main ageing forms and influencing factors of oil-paper insulation for traction transformer were analyzed. The ageing mechanism of oil-paper insulation was studied, the current characteristic parameters characterizing the ageing degree of oil-paper insulation and the main residual life prediction methods were summarized, and the advantages and disadvantages of each characteristic parameter and residual life prediction method and the applicable conditions were analyzed. On this basis, the existing main problems in the ageing state assessment and residual life prediction of oil-paper insulation, as well as the future research directions were discussed.

Organic-inorganic composite dielectrics are often difficult to have both high dielectric constant and high electric strength. In this paper, a sandwich structured composite film was prepared by using aramid nanofibers (ANF) as high-temperature resistant matrix, boron nitride nanosheets (BNNS) as electrical breakdown enhancer, and barium titanate particles (BT) as dielectric modifier through step-by-step vacuum filtration and hot-pressing method, and the effects of sandwich structure and different modifier content on the microstructure and dielectric properties of the composite films were studied. The results show that the sandwich structured composite films have high flexibility and excellent high-temperature stability. The addition of BT decreases the electric strength of single layer and sandwich structured composite films, while the addition of BNNS increases the electric strength of the composite films. The individual addition of BT or BNNS can increase the dielectric constant of composite films at low frequency, while the simultaneous addition of BT and BNNS can increase the dielectric constant in wide frequency domain. Therefore, a composite film with balanced dielectric properties and electric strength can be obtained by adjusting the sandwich structure and modifier content in each layer. When taking the ANF/BNNS film with 10% mass fraction of BNNS as the outer layer and the ANF/BT film with 10% mass fraction of BT as the core layer, the dielectric constant, dielectric loss factor, and electric strength of the prepared composite film is 1.41 (1 kHz), 0.013 (1 kHz), and 13.3 kV/mm, respectively.

In order to improve the bonding strength of epoxy resin potting materials to metals, the effects of molecular structure, amine curing agent type, and inorganic fillers on the tensile shear strength of epoxy resin potting materials were studied. The results show that the epoxy materials prepared by polyurethane modified epoxy resin and dimer-acid modified epoxy resin have higher tensile shear strength. The tensile shear strength of epoxy materials cured by polyamide, polyether amine, and aromatic amine decrease in turn. With the increase of inorganic filler content, the tensile shear strength of epoxy materials increases at first and then decreases. For the nano gas-phase SiO₂ powder, when its filling mass fraction is 4%, the epoxy material has higher adhesive strength, while for the micro powder, its filling mass fraction needs to reach 40%, the epoxy material can have higher adhesive strength.

Light weight and high insulation composite cross-arm has excellent properties of light weight and excellent insulating properties, which has been widely used in power lines in recent years. In this paper, a composite cross-arm with light weight and high insulation of foam core was prepared, and the cross-arm was conducted water absorption, dye penetration, water diffusion leakage current, electric strength, thermal induction, and vibration ageing tests. The results show that the volume water absorption of the composite cross-arm with light weight and high insulation of core is 0.036%, the water diffusion leakage current is less than 75 μA, the AC electric strength is greater than 71 kV/cm, the vibration ageing resistance is good, and the comprehensive performance is better than that of the cross-arm with traditional solid core, which can meet the need of practical engineering application.

A novel low dielectric loss toughening agent (Si-DABPA) was designed and synthesized, and its structure was characterized, then its toughening effect on bismaleimide (DFE950) was studied. The results show that the Si-DABPA and diallyl bisphenol A (DABPA) have the same reactivity to DFE950. Compared with the DFE950/DABPA cured material, the Thermal degradation resistance of the DFE950/Si-DABPA cured material increases, and the dielectric constant (D_k) and dielectric loss factor (D_f) decrease at 10 GHz. Compared with the DFE950/DABPA/PPE cured material, the tensile strenght of the DFE950/Si-DABPA/PPE cured material increases, while the bending strength and impact strength change little.

In order to improve the strength of composite foam material used for post composite insulator core, the poly(p-phenylene benzobisoxazole) (PBO) fiber was used to reinforce composite foam material, and the fiber content suitable for internal insulation applications was determined by studying the effects of different content of PBO fiber on the thermal, mechanical, and insulating properties of composite foam material. The results show that the addition of PBO fiber endows the composite foam materials with the ability to resist impact damage. When the mass fraction of PBO fiber is 0.4%, the energy absorbed by the composite foam materials in the drop weight impact test reaches the maximum. The addition of PBO fiber can decrease the thermal expansion rate of the material, improve the thermal stability, reduce the potential thermal stress risk, and has little effect on the internal insulation performance of composite foam materials.

In this paper, a finite element model of ±400 kV DC wall bushing was firstly established, and the electric field and potential distributions of the DC wall bushing were simulated by COMSOL software. Then the effects of ice edge length, ice cover thickness, and rainfall on the surface electric field of the bushing umbrella skirt were studied. The results show that when the ice edge length increases to bridge the umbrella skirt, the electric field distorts seriously. The increase of ice thickness has little influence on the maximum surface electric field of the umbrella skirt. When the rainfall reaches 10 mm, the maximum surface electric field of the umbrella skirt increases sharply, and the electric field distortion points increase. The research results can provide reference for the development and design of UHV and EHV DC wall bushing.