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.

The buffer layer of high-voltage cable will generate gas products during the ablation process. However, the correlation between the gas product concentrations and conductive property of buffer layer during the ablation process is still unclear at present. Therefore, we conducted a simulated ablation experiment on cable buffer layer and studied the evolution law of current density and gas product concentrations during the ablation process of buffer layer. The results show that under both the dry and wet conditions, the current density of buffer layer exhibits a bi-exponential function decay law with the increase of ablation time, and the decay rate of current density shows a trend of decrease rapidly at first and then unchanged basically with the increase of ablation time, only the wet sample exhibits peak current density during the initial stage of ablation. The gas chromatographic test results show that under the wet condition, the gas products during the ablation process of buffer layers are CO₂, H₂, CO, CH₄, C₂H₄, C₂H₆, and C₂H₂. Under both the dry and wet conditions, the gas product concentrations increase rapidly at first and then tend to a stable value with the increase of ablation time, and the increase time of gas concentration is consistent with the decrease time of current density, which indicates the change laws of current density and gas concentration with the ablation time is closely related. It is analyzed that there is a correlative relationship between the current density decay rate and the gas products generation rate during the ablation process of buffer layer, and the variation of gas product concentration can reflect the severity of buffer layer ablation.

An accelerated thermal ageing test was designed for the main insulation sample of a generator VPI stator bar, and the ultrasonic velocity, ultrasonic spectrum, and ultrasonic defect waveform of samples were analyzed at various ageing temperatures on the basis of the principle of ultrasonic testing. At the same time, artificial hole defects and impurity defects were introduced into the insulation samples to explore the effect of defect introduction on the ultrasonic waveform of the samples. The results show that as the thermal ageing test progresses, the overall ultrasonic velocity in the main insulation of stator bar shows a decreasing trend. The reason is that during the thermal ageing process of the stator bar main insulation sample, the layering of internal structure can cause refraction, reflection, and dissipation of the sound wave during propagation process, resulting in the propagation speed of the sound wave in the insulation sample decrease. The defects can be detected and accurately located through ultrasonic echoes, which indicates that the acoustic performance testing method has good practicality in the diagnosis of stator bar main insulation.

On the basis of surface discharge tests and finite element electric field simulation methods, the surface discharge and electric field characteristics of GIS basin insulators with metal ball or wire particle defects were studied. The results show that under different metal particle defects, both the pulse voltage and ultraviolet photon number increase with the increase of voltage. The surface discharge of basin insulators with metal wire defects is more severe, compared to the situation where there are metal ball defects on the high-voltage side, the discharge is more intense when there are metal ball defects on the low-voltage side, and the change trends of simulation results are consistent with the experimental results. When there are metal particle defects on the surface of GIS basin insulators, the surface discharge intensity is positively correlated with the distortion degree of electric field, and the correlation between the distortion degree of electric field and the average pulse amplitude is significant.

It is found that ablative white spots are often attached to the buffer layer by disassembling high-voltage XLPE fault cables. To study the ablation characteristics of buffer layer, the chemical elements of white spot at different positions of buffer layer were analyzed by using energy dispersive spectrometer (EDS), and the conductivity of the white spots buffer layer were measured. Then on the basis of the measurement results of conductivity, an electrothermal coupling simulation model of high voltage XLPE cable was established, and the heat production characteristics of white spot buffer layer under the action of high frequency overvoltage were calculated. The results show that the white spots in the ablative area of buffer layer are the water-blocking powder precipitated by the buffer layer, and the conductivity of the buffer layer decreases obviously after the white spots are precipitated. Under the action of high frequency overvoltage, the higher the overvoltage frequency, the greater the resistance heat generated in the local periphery of buffer layer white spot, and the higher the temperature rise, which may eventually cause overheating and erosion of the buffer layer.

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.

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.

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.

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 view of the problem and difficulty of isothermal relaxation current method in evaluating the insulation state of distribution cables, a new sample of domestic unaged 10 kV distribution cable was used as the test object in this paper, and the isothermal relaxation current of the cable section and the high-field conductance current of the insulation slice during the 288 hours of accelerated thermal ageing process at 140℃ were detected. The variation trend and range of current relaxation component, ageing factor A, and threshold electric field E_t during thermal ageing were analyzed. The results show that there are three obvious polarization relaxation peaks in the isothermal relaxation current, and the time constants τ₁, τ₂, and τ₃ are in the range of 7-12 s, 31-39 s, and 210-536 s, respectively. During the thermal ageing process, the material traps corresponding to isothermal relaxation current Peak2 and Peak3 change greatly, and the change of Peak3 is the most obvious. The ageing factor A based on the isothermal relaxation current is in the range of 1.72-3.17. The A decreases at first and then increases with the increase of ageing time, and the corresponding conductance threshold electric field E_t shows the opposite trend of rising at first and then decreasing, which indicates that there is a clear correlation between the threshold electric field E_t and the ageing factor A, they are both the macroscopic appearances of internal molecular structure of the insulating material. The ageing factor A of the domestic cable before ageing is 1.91, which is close to the "aged" state of the German standard DIN VDE 0276, and the A drops to 1.72 after ageing for 48 h, which reaches the "better" state of the German standard. The high A of the domestic cable may be related to the residues of cross-linking by-products of cables, so the degassing process should be improved in the production of domestic cables.