With the development of power electronic equipment toward high-frequency, miniaturization, and integration, the performance of traditional polypropylene (PP) film materials is gradually becoming insufficient to meet the requirements of modern capacitors for high electric strength, low dielectric loss, and long service life. To address this, the modified PP film materials with different grafting rates were prepared by grafting 4-methylstyrene onto polypropylene (PP) via an aqueous suspension grafting method, and the effect of grafting rate on their comprehensive properties was studied. The results show that the optimal swelling time and reaction time of grafting modification are 120 minutes and 150 minutes, respectively. With the increase of grafting rate, the heating melting curve tends to shift towards lower temperatures, while the cooling crystallization curve tends to shift towards higher temperatures. When the grafting rate is 0.88%, the modified PP exhibits the highest tensile strength and elongation at break, with the electric strength reaching a maximum value of 400.8 kV/mm, and the trap density reaching a maximum value of 9.52×10¹⁹ m^-³·eV^-1, which is nearly 3.8 times higher than the maximum trap energy level density of pure PP material.

Polyethylene is the preferred material for lithium battery separators, its hydrophilicity directly determines the electrolyte ion transmission efficiency and the interface stability of battery. To improve the hydrophilicity of polyethylene separator, we employed atmospheric pressure plasma jet treatment using 3-aminopropyltriethoxysilane as a reaction medium to activate and modify the separator surface. The effects of treatment time and treatment distance on the hydrophilicity of the separator surface were studied by experiments, and the optimal treatment conditions and effects were obtained. The surface morphology and chemical structure of the separator were characterized using scanning electron microscopy and X-ray photoelectron spectroscopy to analyze the effect of plasma treatment on its micro-physical and chemical properties, thereby analyzing the mechanism of its performance improvement. The results show that with the increase of treatment time and distance, the hydrophilicity of the separator increases at first and then decreases. The optimal performance is achieved at a treatment time of 6 min and a treatment distance of 20 mm, where the water contact angle of the modified separator approaches 0°, achieving super-hydrophilic effect. After treatment, the separator tends to be hard and brittle, and its thermal shrinkage rate decreases by 51%. The plasma jet introduces -NH₃⁺ hydrophilic groups onto the separator surface, and through etching, cross-linking, polymerization, and deposition, a nano-silicon oxide film with larger pores is formed on the material surface, which significantly enhance the surface hydrophilicity and thermal shrinkage resistance of seperator.

This research aims to synergistically enhance the thermal and mechanical properties of epoxy resin to cope with the risk of insulation failure under long-term electrical-thermal-mechanical multi-field coupling conditions. Biphenyl liquid crystal epoxy resin (BLCER) was introduced into the bisphenol A type epoxy resin (E-51) matrix, and liquid crystal-modified epoxy resin was obtained through melt blending followed by curing. The thermal and mechanical properties of the modified resin were tested, and the toughening and thermal conductivity modification mechanisms of BLCER on the resin matrix were analyzed. The results show that the addition of BLCER can enhance the thermal stability and thermal conductivity of the modified resin. When the mass fraction of BLCER reaches 20%, the thermal conductivity of the modified resin increases to 0.382 W/(m·K), which is 2.26 times higher than that of pure E-51. The mechanical properties of the material increase with the content of BLCER. When the mass fraction of BLCER reaches 20%, the tensile and flexural strengths of the modified resin reach 90 MPa and 120.9 MPa, respectively, and the impact strength reaches 40.1 kJ/m², which are significantly higher than those of pure epoxy resin.

Cross-linked polyethylene (XLPE) submarine cable is a key transmission equipment in flexible low-frequency transmission scenarios such as medium and long-distance island transmission and offshore wind-solar new energy power generation. In this paper, XLPE insulated cable was conducted electrothermal ageing tests under low frequency voltage, and the effects of ageing voltage frequency on the electrical properties, mechanical properties, and micro-structure of XLPE insulation were studied. The results show that when the ageing voltage frequency is 10-50 Hz, the AC electric strength, volume resistivity, and elongation at break of XLPE ageing samples increase at first and then decrease with the increase of ageing voltage frequency. The electrical properties of XLPE samples aged under 20 Hz and 30 Hz of voltages are better than those aged under other voltage frequencies. The change trend of crystallinity of XLPE ageing samples with ageing voltage frequency is consistent with the electrical properties. The thermal ageing at lower voltage frequency contributes to the recrystallization of XLPE insulating materials, while the thermal ageing at higher voltage frequency will damage the crystalline structure of the material and increase the proportion of amorphous regions. The research results can provide a reference for the applicability of XLPE insulated cables in low frequency transmission technology.

Degassing heat treatment is the longest process in the production of cross-linked polyethylene (XLPE) cables, and reducing degassing time is an important way to improve cable production efficiency. Focused on the migration of residual by-products in XLPE insulating materials for high-voltage cables, we established a diffusion model of cross-linked by-products driven by concentration gradient. The concentration of by-products in the insulation of a 320 kV DC cable after degassing was measured and compared with the simulation results, and the effects of temperature and initial concentration of by-products on the degassing process were investigated. The results show that the simulation and measured results of the concentration distributions of methane and acetophenone in the 320 kV DC cable after degassing are essentially consistent, verifying the correctness of the model. Higher temperatures can accelerate the degassing process of by-products. Within the temperature range of 65-75℃, for every 5℃ increase in temperature, the degassing time for methane is shorten by approximately 30%, and the degassing time for acetophenone is shorten by approximately 72 h. Reducing the initial by-product concentration can also shorten the cable degassing time. It is an important way to reasonably regulate the initial concentration of by-products and degassing temperature for optimizing the cable degassing process and improving enterprise efficiency.

In order to obtain the characteristic gases generated during the decomposition of cross-linked polyethylene (XLPE) at different stages under electrical and thermal factors to judge the degree of degradation, we systematically studied the gas production characteristics of XLPE under thermal field and electrical field through thermogravimetric-infrared (TG-IR) experiments, high-energy discharge gas production experiments, and molecular dynamics (MD) simulations based on reactive force field (ReaxFF). The results show that under the action of thermal field, XLPE primarily decomposes to generate ethylene, propylene, and long-chain hydrocarbons, accompanied by oxidation products such as CO and CO₂. While under the action of electrical field, the characteristic gases are mainly acetylene and propyne, and distinct absorption peaks of propyne appear in the infrared spectrum under high-energy discharge. Molecular simulation further reveals the differences in decomposition pathways of XLPE under electric and thermal fields. Specifically, decomposition under the thermal field is dominated by end-group breakage, while the electric field accelerates free radical reactions and promotes the generation of highly unsaturated substances. Finally, a normalized characteristic gas infrared spectrum library is constructed through density functional theory (DFT) calculation. The gas production process is divided into different stages based on the turning point of thermogravimetric curve, the peak spectrum change temperature of gas infrared spectrum, and the molecular simulation trajectory time of the decomposition process. This study clarifies the characteristic gases of XLPE during electrical/thermal decomposition and the gas production mechanisms, which can provide a theoretical basis for the fault detection of XLPE cable based on gas infrared spectrum.

In this paper, a novel crosslinked network cellulose insulating paper was prepared by citric acid crosslinking modification, and the dielectric constant and dielectric loss factor of the insulating paper were measured before and after modification. Then the composite insulation system of the modified insulating paper and mineral insulating oil were carried out partial discharge and electrical life tests. The results show that compared with the unmodified insulating paper, the dielectric constant and dielectric loss factor of the novel crosslinked network insulating paper decreases by 15.39% and 29.78%, respectively, and the electrical life index increases by 37.94%. The novel crosslinked network insulating paper-insulating oil composite insulation system has lower discharge repetition rate, discharge energy, average discharge, and maximum discharge.

In order to investigate the performance degradation characteristics of multi-layer Nomex insulating paper used in transformers during the thermal ageing process, firstly, the multi-layer oil-immersed Nomex insulating paper was conducted accelerated thermal ageing test, then a frequency domain dielectric spectroscopy testing platform and a surface potential testing platform were established to obtain the dielectric loss factor and surface potential decay curves of oil-immersed insulating paper at different ageing time, and the surface trap distribution characteristics of the oil-immersed insulating paper with different ageing degree were calculated and analyzed. The results show that with the increase of thermal ageing degree, the dielectric loss factor of oil-immersed Nomex insulating paper samples increases significantly across all frequency bands. The dielectric loss factors of double-layer and triple-layer oil-immersed insulating paper samples are significantly higher than that of single-layer oil-immersed insulating paper sample, and the dielectric loss factor of triple-layer oil-immersed insulating paper sample exhibits an even greater increase. As the thermal ageing degree increases, the initial surface potentials of the insulating paper samples gradually decrease, and the surface potential decay rate increases with ageing time, while at the same ageing cycle, the surface potential decay rate gradually decreases with the increase of insulating paper layer number. The shallow trap density of oil-immersed insulating paper increases with the increase of ageing degree, while the deep trap density decreases. The decline rates of deep trap density and energy level of double-layer oil-immersed insulating paper are lower than those of single-layer oil-immersed insulating paper, while the increase rates of its shallow trap density and energy level are higher than those of single-layer oil-immersed insulating paper. The research results can provide some reference for the design of transformer oil-paper insulation.

In order to evaluate the application potential of environmentally friendly polypropylene materials in high-voltage cable accessories, the electrical properties include electric strength, space charge distribution, and polarization current of novel polypropylene insulating material and silicone rubber under typical operating conditions were studied to assess their voltage withstand capability, charge accumulation behavior, quasi-steady-state polarization current. At the same time, a 110 kV cable joint simulation model was established using finite element simulation software to simulate the electric field distribution at the joint, and the application performance of polypropylene/silicone rubber composite insulation in high-voltage AC cable joints was explored. The results show that the novel polypropylene exhibits excellent electric strength, although the electric strength decreases with the increase of temperature, it still remains 88.80 kV/mm at 90℃. The electric strength of the polypropylene/silicone rubber composite insulation is primarily influenced by the silicone rubber, but it exhibits good thermal stability and maintains 39.70-47.01 kV/mm within 30-90℃. Space charge test reveals that the polypropylene still has significant charge suppression ability under 20 kV/mm, which can effectively improve the electric field distortion at the composite interface. Calculation based on simulation model indicates that the internal electric field distribution in the 110 kV cable joint using this composite insulation is reasonable, and the maximum electric field strength at the polypropylene/silicone rubber interface is only 5.7 kV/mm, which is far lower than its electric strength. The research has confirmed that the reliability of the novel polypropylene/silicone rubber composite insulation structure meets the operational requirements of high-voltage cable joints.

In order to evaluate the thermal ageing of silicone rubber for cable intermediate joint insulation layer, this paper proposed an evaluation method based on nonlinear ultrasonic signal characterization. Firstly, a ultrasonic detection simulation model of silicone rubber ageing was established, and tests were conducted on the real cable joint specimens with different thermal ageing time at 200℃. Then the nonlinear ultrasonic detection was carried out at typical positions by using wedge coupling method. Lastly, the correlation between the ageing time and ultrasonic nonlinear coefficient was verified and the mechanism was explored. The results show that the experimental and simulation results are highly consistent in the change trends of the characteristic parameters of transmitted wave signal in time-domain and frequency-domain. Specifically, as the ageing time increases, the fundamental wave amplitude and the second harmonic amplitude both gradually decrease, and the ultrasonic nonlinear coefficients gradually increase. Under actual ageing time of 480, 720, and 960 h, the relative errors between the ageing time of silicone rubber obtained by substituting the nonlinear ultrasound coefficients obtained from the experiment into the fitting relationship equation and the actual ageing time are 1.58%-5.66%, 2.57%-6.66%, and 0.85%-4.75%, respectively, and the consistency between the fitted results and the actual ageing time is better, which verifies the validity of nonlinear ultrasonic testing method in the assessment of thermal ageing damage of silicone rubber.