In this paper, the effects of properties of chopped fiber on the breakdown strength, conductivity, trap characteristics, and mechanical properties of meta-aramid paper were studied. The results show that based on the reference sample of which the fiber diameter is 25 μm, fiber length is 6 mm, crystallization temperature is 300℃, and the ratio of precipitated fibrids and chopped fibers is 7:3, when the fiber diameter increases to 45 μm, the embedding degree of chopped fibers decreases, interface pores appear, and the breakdown and tensile strength of aramid paper can decrease by 16% and 24%, respectively. When the length of fiber increases to 18 mm, chopped fiber morphology shows coiling-type thus forming the "hard-form" interface, the breakdown strength of aramid paper decreases by 63%, while the tensile strength shows little change. When the crystallization temperature decreases to 230℃, the structural stability of chopped fibers reduces, which causes their melting under hot-pressing process, and the breakdown strength and tensile strength decreases by 36% and 50%, respectively. With the increase of proportion of chopped fiber, the breakdown strength of aramid paper increases at first and then decreases, which is along with the change of paper compactness, while the tensile strength of aramid paper increases monotonically with the increase of chopped fiber content, which reflects the necessity of chopped fibers for the stable molding of aramid paper and the weakening effect of excessive chopped fibers on electrical insulation. In addition, the aramid papers with low breakdown strength show a higher conductivity and a shallower trap depth, which can be regarded as reference indexes for the insulation performance of meta-aramid papers.

With a high voltage grade and large transmission capacity, ultra-high voltage (UHV) gas insulated metal enclosed transmission line (GIL) needs insulator with higher resistance to the comprehensive effect from electric, heat, and force. In this paper, epoxy composite materials were prepared by doping micro-Al₂O₃, micro-SiO₂, and micro-Al₂O₃-SiO₂ blend fillers, respectively. The mechanical, thermal, and electrical properties of the blend system were tested and analyzed. The results show that with the increase of the volume proportion of Al₂O₃, the comprehensive mechanical properties of the composites are improved, and pure micro-Al₂O₃/epoxy composite exhibits the best mechanical properties. Doping two fillers improves the thermal conductivity and arc resistance of the composites, but slightly reduces the glass transition temperature and increases the thermal expansion coefficient. When the volume ratio of Al₂O₃ and SiO₂ in composites is 1:1, the arc resistance duration and the thermal conductivity of the composite reaches 1.198 W/(m·K） and 186.63 s, respectively. With the increase of the volume proportion of SiO₂, the dielectric constant of the composites decreases, while the breakdown strength increases. The power frequency breakdown strength of the pure micro-SiO₂/epoxy composites is the highest, reaching 36.63 kV/mm.

In order to analyze the effects of rutile nano-TiO₂ doping on the properties of polyethylene (PE) materials from the microscopic perspective, PE and TiO₂/PE composite models with different mass fractions of water molecular were constructed by using molecular dynamics simulation method. And then taking temperature as a variable, the thermodynamic properties and microstructure of PE before and after being modified by nano-TiO₂ and the diffusion ability of water molecules in the composite system were analyzed. The results show that after doping with nano-TiO₂, the glass transition temperature of PE system increases by 33 K, the Young's modulus increases by 428.17%, and the shear modulus increases by 338.62%. Nano-TiO₂ greatly inhibits the movement of PE molecular chain and the diffusion of water molecules, which increases the stability of the composite system. The addition of water molecular and the increase of temperature decrease the thermodynamic properties of the composite system, both of which destroy the stability of the composite system.

By using organic-inorganic composite technology, the high temperature resistant insulation layer was prepared by coating quartz fiber wrap cladding with silicone nano alumina sol. The micro morphology and structure of the organic silicon-nano alumina sol coating were analyzed by SEM, FTIR, XRD and other characterization techniques. The thermal stability of the organic silicon-nano alumina sol composite insulating paint was analyzed by TG-DSC. The insulation performance and breakdown voltage performance of high-temperature wire were tested at room temperature and high temperature. The results show that the organic silicon-nano alumina sol composite insulating paint has good thermal stability, and it can significantly improve the temperature resistance level of the glass fiber wrap cladding. The high-temperature wire shows good high temperature insulation and high voltage resistance. At 800℃, the electrical resistance is greater than 1 MΩ·m, and the normal temperature breakdown voltage is greater than 2 000 V. It is suitable for special environments such as high temperature and high voltage in the aviation and aerospace fields.

In the preparation of tetragonal nano-barium titanate powder by traditional solid-phase method, the dispersion and particle size of the BaCO₃ precursors play a crucial role in the morphology, particle size, and dielectric properties of the obtained tetragonal BaTiO₃ nanoparticles. In this paper, nano BaCO₃ powders were prepared by controlling the concentration of the Ba(OH)₂ using Ba(OH)₂ and drikold as raw materials. Then, BaTiO₃ powders and ceramic were prepared using the BaCO₃ powders, and the dielectric properties of BaTiO₃ ceramic was studied. The results show that the short rod-shaped nano BaCO₃ powders with a particle size of 180 nm and the highly dispersed, highly uniform and pure tetragonal BaTiO₃ powders with a particle size of 400 nm were prepared. The dielectric constant and dielectric loss factor of the BaTiO₃ ceramic obtained by calcination at 1 250℃ is 4 885 and 0.018 9, respectively.

In this paper, the oil resistance reliability of impregnated resin, enameled flat wire, and aramid fiber paper for oil-cooled motors was studied, and the performance changes of insulating materials after long-term contact with automatic transmission fluid (ATF) under high temperature conditions were investigated. The results show that the insulating materials are greatly affected by the moisture in ATF in the oil resistance test, water and air can promote the hot oxygen ageing of ATF to generate acidic substances, which can accelerate the hydrolysis of material. After conducting high-temperature oil resistance test for 2 000 h, the two impregnating resins, enameled flat wire D and two aramid papers show excellent oil resistance and good reliability.

In order to analyze the influence of natural ester insulating oil on the insulation performance of high-voltage transformer, in this study, a 220 kV power transformer was taken as the research object, the wave process calculation was carried out on it to obtain the node potential and oil channel gradient voltage under the full wave of lightning impact. And the electric field distribution under power frequency and full wave voltage of lightning was obtained by establishing a calculation model of transformer main insulation electric field, and then the insulation margin was calculated. The results show that the main insulation margin of natural ester insulating oil transformer is large at power frequency, while it is small at full wave of lightning. By improving the insulation structure of natural ester insulating oil transformer, the main insulation distance between medium voltage and high voltage windings of the natural ester insulating oil transformer is reduced by about 6%; the minimum insulation margin under the full wave of lightning can be increased by 15% by increasing the insulation thickness and radius of the winding turn, and the cost is saved effectively.

Polarization-depolarization current (PDC) method is widely used to evaluate the insulation status of cross-linked polyethylene (XLPE) cables. However, the existing studies tend to use a single dielectric characteristic parameter to reflect the ageing condition of insulation, which does not make full use of the rich dielectric response information in PDC results, and a single dielectric parameter is difficult to apply to different ageing types. To solve the above problems, an improved radar spectroscopy evaluation method was proposed to evaluate the insulation condition of XLPE cable by comprehensively utilizing multidimensional dielectric parameters. To verify the effectiveness of the proposed method, PDC test was conducted on short XLPE cable specimens after being artificially accelerated thermal and water tree ageing. Then the PDC results were analyzed by the proposed multidimensional dielectric parameter radar spectroscopy method. The results show that the area parameter of polygon in radar chart can effectively reflect the degree of ageing in both types of aged XLPE cables.

Simulation calculations were conducted on the stator bars and windings of generator in a high altitude area by establishing a simulation model, and the rationality of the anti-corona design of the stator bar and winding was explored. According to the design, the stator bars and windings were manufactured and the reliability of the anti-corona structure was further verified through experiments. The simulation calculation results show that when the altitude is 3 000 m, the maximum field strength of the stator bar during the operation voltage, anti-corona assessment voltage, and voltage withstand process is 0.32, 0.44, and 0.53 kV/mm, respectively, and the maximum loss is 2.19×10⁵, 1.46×10⁶, and 6.34×10⁶ W/m³, respectively. The maximum electronic density between the layers of the generator winding is 1.32×10¹⁷ m^-3. After the modification of the oblique clearance of the stator winding, the maximum field strength of the stator bar during the operation voltage, anti-corona assessment voltage, and voltage withstand process is 0.78, 1.50, and 2.14 kV/mm, respectively, and the maximum loss is 3.01×10⁵, 6.8×10⁵, and 3.23×10⁶ W/m³, respectively. The experimental results show that the stator bars can pass the corona test under 40.7 kV and the withstand voltage test under 73.5 kV for 1 minute. With the increase of altitude, the ultraviolet photon number of the winding at 1.1U_n increases gradually, while that number is less than 1 000 when the altitude is below 3500 m. The anti-corona performance of the designed winding meets the design and operation requirements of the unit.

In this study, EPDM seal ring commonly used in gas insulated switchgear (GIS) equipment was treated at -55℃, and the effects of low temperature on its surface morphology, structure, glass transition temperature, and mechanical properties (tensile and compression permanent deformation) were investigated. The results show that the low temperature treatment cannot damage the macromolecular chain structure in the seal ring, but it is easy to cause frosting, and the glass transition temperature shows an increasing trend. The mechanical properties of the seal ring change greatly after low temperature treatment, the hardness and breaking strength decrease, while the elongation at break and compression permanent deformation increase. The degree of change in tensile property is related to the amplitude of alternating temperature difference in alpine environment, the greater the amplitude, the greater the breaking strength loss of the seal ring.