To improve the dielectric properties of polypropylene (PP), different mass fractions of β-nucleating agent and nano-montmorillonite (MMT) were added into a PP matrix in this paper to construct various ternary composite systems β-MMT-PP, and the synergistic effect of the two on the microstructure and dielectric properties of PP was investigated. The modified PP materials were characterized by means of X-ray diffractometry (XRD), differential scanning calorimetry (DSC), polarizing optical microscopy, pulsed electro-acoustic (PEA) method, conduction current, and DC breakdown tests. The results indicate that the addition of an appropriate amount of β-nucleating agent and MMT can effectively improve the microstructure of PP. When the mass fractions of β-nucleating agent and MMT are 0.5% and 1.0%, the β-crystal content and crystallinity in the composite system reach their peak values of 84.01% and 55.4%, respectively. With the addition of β-nucleating agent and MMT, both the space charge injection threshold field strength and the breakdown strength of PP are improved, reaching maximum values of 19.73 kV/mm and 94.99 kV/mm, respectively. An appropriate amount of β-nucleating agent can induce the transformation from α-crystal form to β-crystal form and refine the spherulites, thereby better improving the dielectric properties of the material.

This study aims to clarify the effects of the crystallization characteristics of domestically washed polypropylene resin and the casting process on the microstructure of cast films and the comprehensive properties of biaxially oriented polypropylene (BOPP) films. Using domestically washed polypropylene resin as the research object, the effects of crystallization characteristics of the domestic resin and casting process on the regulation of the cast film microstructure and the resulting effects on the comprehensive properties of BOPP films were systematically investigated by means of characterization techniques such as polarizing optical microscopy (POM) and wide-angle X-ray diffractometry (WAXD). The results show that the domestic resin can form β-crystals of relatively small size during slow cooling. Increasing the chill roll temperature can increase the crystallinity, β-crystal content, and spherulite size of the cast film, while the β-crystals on the cast film surface directly influence the size and distribution morphology of the crater rings on the surface of the domestic BOPP film. The comprehensive properties of the domestic BOPP film have approached those of imported products of the same specification.

To prepare epoxy resin-based composites with excellent comprehensive properties, this study synthesized dendritic nanosilica (DSiO₂) via a dual-template method and applied them to modify epoxy resin (EP). The relationship between structure and property of the composites was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption-desorption tests. The results indicate that after modification with the silane coupling agent Z-6040, DSiO₂ exhibits excellent dispersibility in epoxy resin. As the mass fraction of DSiO₂ increases from 0 to 0.9%, the onset curing temperature of the composite decreases from 160.7℃ to 111.3, and the peak temperature decreases from 196.3℃ to 159.6℃; the tensile strength increases from 24.2 MPa to 53.6 MPa, the elongation at break increases from 10.5% to 13.5%, and the Rockwell hardness increases from 85.1 to 91.5. Compared with the unmodified EP, the DSiO₂/EP composites exhibit significantly increased storage modulus, a glass transition temperature (T_g) that shifts toward higher temperature, and enhanced thermal stability.

To address the dielectric matching problem in the oil-paper insulation system composed of cellulose insulating paper and low-permittivity insulating oil, this study employed low-temperature plasma for the surface treatment of insulating paper to improve the oil-paper insulation performance. A nanosecond pulse power supply was used to drive dielectric barrier discharge (DBD) to generate Ar/HMDSN plasma, and the effects of operating parameters such as precursor flow rate and treatment time on the properties of insulating paper and oil-paper insulation were investigated. The changes in surface physicochemical characteristics were analyzed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to explore the mechanism of property changes of the insulating paper. The results show that the insulation and mechanical properties of the insulating paper first increase and then decrease with the increase of precursor flow rate and treatment time, with the most significant improvement achieved after treated for 6 min under the flow rate of 15 mL/min. Compared with the untreated insulating paper, the relative permittivity of the insulating paper treated under these conditions decreases by 35.7%, the tensile strength increases by 23.1%, the flashover voltage and breakdown strength increase by 34.2% and 25.0%, respectively, and the flashover voltage and breakdown voltage of oil-paper insulation is correspondingly improved by 24.4% and 17.2%. During the plasma treatment process, low-polarity molecular fragments generated from the reaction precursor can penetrate the insulating paper and undergo deposition polymerization on the fiber surface, reducing molecular polarity, thereby comprehensively improving the both the surface and the bulk insulation properties of insulating paper.

To develop composite separator materials with excellent flame retardancy, electrical properties, and mechanical properties to meet the safety requirements of power battery systems for new energy vehicles, we prepared a series of ATO/PS composites by adding different mass fractions of nano antimony tin oxide (ATO) to polystyrene (PS). The micromorphology, mechanical properties, flame retardancy, electrical properties, and corrosion resistance of PS and ATO/PS composites were systematically compared. The results show that when the ATO mass fraction is 4%, the ATO/PS composite achieves the best comprehensive performance. Compared with pure PS, its tensile strength, elongation at break, flexural strength, and impact strength increase by 27.75%, 36.71%, 20.31%, and 26.54%, respectively; the flame retardancy is significantly improved, with the limiting oxygen index increasing by 23.7% and the UL-94 rating upgrading from NR to V-0; in terms of electrical properties, the volume resistivity decreases by 77.5% and the dielectric loss factor decreases by 51.5%. When the ATO mass fraction is 5%, excessive ATO leads to a decline in mechanical properties due to the agglomeration effect, and the improvements in flame retardancy and electrical properties slow down.

To systematically investigate the short-term and long-term DC voltage endurance characteristics of polypropylene (PP) materials, we took PP sheet specimens as the research object and tested their DC breakdown strength at different temperatures and thicknesses. Through linear voltage ramp and stepwise voltage ramp tests, the effects of voltage application method and ramp rate on the DC breakdown strength of the specimens were studied. On this basis, combined with the breakdown test data under constant voltage, the DC voltage endurance coefficients of the material determined by different voltage application methods were compared, and the applicability of each method was analyzed. The results show that as the temperature increases, the DC breakdown strength of the PP specimens decreases, which conforms to the Arrhenius equation. As the specimen thickness increases, the breakdown strength decreases following an inverse power law. The faster the voltage ramp rate, the higher the measured DC breakdown strength. As the voltage application time increases, the breakdown strength of the specimens decreases. The DC voltage endurance coefficient of the PP material determined by the inverse power law of electrical ageing based on the data from the constant voltage method and the stepwise voltage ramp method is approximately 13.

To address the key problems in ultra-high voltage flexible DC transmission system that the core biaxially oriented polypropylene (BOPP) films for dry-type DC capacitors rely on imports, and the high ash content of domestic polypropylene resins leads to insufficient insulation and ageing resistance of the films, we selected imported electrical-grade, domestic continuously washed low-ash, and domestic unwashed high-ash polypropylene resins to prepare BOPP films. The microscopic morphology, crystal structure and electrical properties of the films were characterized systematically, and the combined electro-thermal ageing tests under AC-DC superimposed conditions were conducted. The results show that BOPP films prepared from low-ash domestic washed polypropylene resin have higher electric strength and more stable high-temperature dielectric performance. Moreover, the crystal structure of the films has no significant changes after ageing, and their electrical properties are close to those of the imported BOPP films.

To address the challenge of on-site, non-destructive, and live assessment of the mechanical life of distribution cable outer sheaths, a thermal ageing platform and a hygrothermal accelerated ageing platform were established in this paper, and the evolution law of the compression modulus of PVC sheaths with ageing time and multi-stress coupling effects was systematically investigated. Based on the changing law of compression modulus, an Arrhenius single-stress ageing model and a Peck hygrothermal coupled ageing model were constructed, and the prediction errors of the two models were compared; meanwhile, an on-site sampling scheme with radial and axial multi-point sampling was proposed. The results show that the compression modulus increases exponentially with ageing time, while the elongation at break decreases rapidly. At 120℃, the degradation rate at 60% relative humidity is significantly higher than that at 40% relative humidity, and the humid environment can further accelerate the rigid-to-flexible transition process of the material. Under hygrothermal environments, the Peck hygrothermal coupled model can significantly reduce the prediction errors compared with the Arrhenius model. The error of radial and axial multi-point sampling on the cable can be reduced to 4.1% compared with the traditional specimen testing.

Metal particles are easily generated during the installation and operation of DC gas-insulated transmission lines (GIL). Under electrodynamic forces, the particles may contact with insulators, causing electric field distortion on the insulator surface, partial discharge, or even insulation breakdown, which seriously threatens the safe operation of GIL equipment. Based on a coupled electric field-flow field mathematical model for DC GIL, combined with the motion trajectories of metal particles inside the DC GIL, the feasibility of an lifting type particle trap as a particle movement suppression scheme was investigated. The results show that after installation of particle trap, the jumping motion of most particles is suppressed. The electric field strength in the bottom area of the trap is significantly reduced, but the degree of electric field distortion increases at the top area of trap, and insulator and high-voltage conductor, indicating that a balance between the electric field shielding range and distortion risk must be considered when designing trap parameters. By optimizing trap parameters such as lifting height, grid width, baffle width, and distribution angle, the low-field-strength coverage area can be expanded, which enhances the electric field shielding effect and particle movement suppression capability of the trap, and reduces the proportion of escaped particles.

Dry air is widely used as an alternative to SF₆ gas in gas-insulated switchgear (GIS). However, metallic particle contamination is a key issue that restricts the development of high-voltage GIS. In this paper, a model for predicting the cumulative breakdown probability of high-voltage air gaps was established on the basis of time-volume theory, and the influence of metallic particles on the breakdown characteristics of high-voltage dry air gaps at high voltage levels was studied. The results show that metallic particles located near the electrodes are more likely to cause gap breakdown, and those near the high-voltage electrode are more likely to cause breakdown than those near the grounded electrode. Meanwhile, particles with sharp protrusions are more likely to cause gap breakdown than round particles. Therefore, in the design of gas-insulated equipment, particle traps or barriers should be used to keep metallic particles away from the electrodes, and the occurrence of particles with sharp protrusions should be avoided as much as possible.