With the rapid development of modern electrical equipment, higher requirements have been put forward for nanocomposite films with higher dielectric strength and mechanical properties. Therefore, we modified boron nitride nanosheets (BNN) with 3-aminopropyltrihydroxysilane to obtain modified BNN (aBNN), and then mixed aBNN with aramid nanofiber (ANF) to prepare dense ANF/aBNN nanocomposite films by high-temperature hot-pressing method. The thermal stability, mechanical properties and electrical insulating properties of films were characterized. The results show that with the increase of aBNN content, the thermal weight loss rate of the nanocomposite film decreases significantly. When the mass fraction of aBNN is 10%, the tensile strength, elongation at break, and toughness of the ANF/10%aBNN nanocomposite film reach the maximum value, which is 235 MPa, 14.0%, and 32.4 MPa·m^1/2, respectively, it is 25%, 9.4%, and 75.1% higher than that of ANF/10%BNN, respectively. The electrical strength of ANF/10%aBNN is as high as 154 kV/mm, which is about 15% and 11.6% higher than that of pure ANF and ANF/10%BNN, respectively. And the volume resistivity reaches the maximum value of 7.94×10¹⁷ Ω·cm (tested at 60℃), which is 893% and 694% higher than that of pure ANF and ANF/10%BNN, respectively.

To investigate the influence law and mechanism of polyethylene glycol diglycidyl ether (PEGDGE) on the mechanical and thermal properties of epoxy materials for insulated pull rods, molecular dynamics simulations were used to calculate and analyze the macroscopic properties and microscopic structural parameters of epoxy resin cross-linked systems with PEGDGE mass fractions of 0, 5%, 10%, 15%, and 20% (percentage of epoxy resin mass), respectively. The effect of PEGDGE content on the mechanical and thermal properties of epoxy materials for insulated pull rods was summarized, the influence mechanism was elucidated from the perspective of system structure, and the calculation results were verified through experiments. The results show that with the introduction of PEGDGE, the glass transition temperature, tensile strength, and bending strength of epoxy resin, as well as the viscosity of castable decrease, while the impact strength of epoxy resin increases. When the mass fraction of PEGDGE is 5%, the material shows the best comprehensive performance. PEGDGE molecules with high flexibility increases the free volume fraction, mean square displacement, and the ratio of bulk modulus to shear modulus (K/G) of the epoxy resin system, which enhances the mobility of molecular segments, and leads to the increase of toughness and the decrease of rigidity of the epoxy resin material.

In order to solve the problem of significant decrease of insulation performance caused by condensation on the surface of switchgear insulation components in high temperature and high humidity environments, in this paper, E51 epoxy resin was modified by adding different mass fractions of nano-alumina, and the electrical properties of the modified samples were tested. The results show that the resistivity and dielectric loss factor of the modified epoxy resin decrease slightly. In the condensation environment formed under different temperature difference, the flashover voltage of the modified epoxy resin clean sample with nano-alumina mass fraction of 1%, 3%, and 5% is 56.7%, 84.5%, and 66.7% higher than that of unmodified sample, respectively. With nano-alumina mass fraction of 1%, 3%, and 5%, the flashover voltage of the contaminated sample is 10.8%, 17.3% and 14.9% higher than that of unmodified sample, respectively, and the effective value of the leakage current is 40.3%, 46.6% and 45.8% lower than that of unmodified sample, respectively. In summary, the electrical properties of modified epoxy resin samples containing 3% nano-alumina are improved significantly.

In this paper, epoxy resin bulk molding compound (EP-BMC) was prepared by mixing short cut glass fibers and calcium sulfate whiskers with epoxy resin matrix. After molding and curing, the influence of glass fiber filler ratio on the wear resistance, mechanical properties, and dimensional stability of EP-BMC material was researched. The results show that with the increase of glass fiber filler ratio, the wear resistance and the linear expansion coefficient of EP-BMC material after thermal ageing decrease continuously, while the tensile strength and bending strength increase at first and then decrease. When the mass ratio of glass fiber to filler is 30∶40, the EP-BMC material shows optimal comprehensive performance. After thermal ageing, the volume wear is 1.00 mm³, the tensile strength and bending strength is 56 MPa and 145 MPa, respectively, the linear expansion coefficient is 24.94 μm·m^-1·℃^-1, and the volume resistance reaches 2.0×10¹³ Ω.

Insulating materials are prone to flashover along the surface due to their inherent properties, contamination accumulation, rain and snow, and so on. In this paper, a multifunctional nanocomposite coating (SiO₂/MWCNTs/PDMS) was prepared through a "polymer+nanofiller" method by using polydimethylsiloxane (PDMS) elastomer as the matrix, SiO₂ nanoparticles and multi-walled carbon nanotubes (MWCNTs) as fillers. The trap distribution, DC surface flashover voltage, and hydrophobicity of the nanocomposite coating were tested and analyzed. The results show that the composite coating has a high surface roughness, which hinders the development of surface discharge. The surface flashover voltage of the composite coating increases from 17.7 kV to 24.3 kV, with a growth of 37.3%. With the increase of SiO₂ and MWCNTs content, the water contact angle of the composite coating has no obvious change the maximum water contact angle reaches 150.5°, and the composite coating has good self-cleaning ability. The research results can provide reference for the engineering application of composite insulation coating materials in the future.

The electric field distribution of cable joints under DC operation is influenced by the conductivity of insulating materials, which exhibits non-linear characteristics under the effects of temperature and electric field, so the electric field distribution within the joints is exceptionally complex. In order to select or determine suitable insulating materials for joint in engineering applications and improve the electric field distribution inside the joint, we constructed a simulation model for the prefabricated joint structure of 10 kV voltage level XLPE-insulated DC cables. By changing the non-linear characteristic parameters of the conductance of silicone rubber, the influence of the conductance activation energy and conductance field strength dependence of silicone rubber on the electric field distribution inside the joint under full load operation was explored. The results show that under high load conditions, the DC steady-state field strength at the insulation interface of the joint is influenced by the conductance activation energy and the conductance field strength dependence of the insulating material, the conductance activation energy has a greater impact. From an economic perspective, the ratio of the conductance activation energy and field strength dependence coefficient of conductance between silicone rubber and XLPE insulating material should not be higher than 0.94 and not be lower than 0.50, respectively.

In order to explore the ageing resistance of nitrile rubber products, such as high-temperature resistance, transformer oil resistance, and heat-compression resistance, we conducted accelerated ageing tests on nitrile rubber (NBR) under high temperature conditions of 90, 120, and 135℃ in hot air, hot oil, hot air compression, and hot oil compression, respectively. The effects of ageing temperature, ageing time, and ageing environment on the mechanical properties of NBR were researched, and compression set was used as an evaluation index to predict the actual service life of NBR. The results show that the ageing rate of NBR increases with the increase of temperature. During the ageing process, with the increase of ageing time, the Shore hardness and compression set of NBR increase, while the elongation at break decreases. 25^# transformer oil can slow down the decrease in Shore hardness and compression set performance of NBR, while it slows down the decrease at first and then accelerates the decrease in fracture elongation. Based on the Arrhenius law, the predicted service life of NBR in hot oil compression environment at temperatures of 40, 50, 60, 70, and 80℃ is 3.726, 1.877, 0.985, 0.542, and 0.303 years, respectively.

In order to investigate the influence of copper and insulating paper on the properties of alkylbenzene insulating oil inside oil-filled high-voltage cables, alkylbenzene insulating oil was placed in four different environments and subjected to a thermal ageing experiment at 120℃ for 50 days. Ageing characteristic parameters of oil sample such as acid value, dielectric loss factor, interfacial tension, and water content were measured during the ageing process, and the correlation between the four indicators was studied using regression analysis. The results show that as the ageing time increases, the ageing degree of oil sample intensifies, copper accelerats the ageing of alkylbenzene insulating oil, while insulating paper has no significant effect on the ageing of the oil. The dielectric loss factor of insulating oil is positively correlated with its acid value and water content, and negatively correlated with interfacial tension, both of which are exponential functions. The regression fitting equation is y=A₁·exp(±x/t₁)+y₀, and the goodness of fit is greater than 0.94. In the results of multiple linear regression, there is a common constraint relationship between the dielectric loss factor, acid value, interfacial tension, and water content.

In order to reduce the use of greenhouse gas SF₆ in switchgear, we designed a 126 kV environmental friendly GIS by an insulating scheme using "vacuum disconnect + clean air", and focused on researching the insulation performance of its isolated grounding switch. Firstly, the breakdown characteristics of clean air insulation medium under different working pressure conditions were researched based on verification test of SF₆ busbar insulation, and the allowable design field strength value of clean air insulation medium was determined based on this characteristic. Then, the working pressure of environmentally friendly GIS (0.65 MPa) was determined by utilizing the allowable field strength value and equipment size. Finally, taking the allowable design field strength requirement of clean air at 0.65 MPa as the constraint condition, a simulation model was constructed to research the influence of the structural design of the isolated grounding switch on its internal electric field distribution characteristics. The results show that the chamfer position at the edge of the isolated contact and the three-phase junction of the air, conductor, and epoxy material of the basin insulator are the weak links in insulation. Combined with the verification test of the GIS prototype, the insulation performance of the environmental friendly GIS isolated grounding switch designed in this paper meets the design requirements, and the method for determining the allowable field strength of the clean air insulation medium is reasonable and sufficient.

Aiming at the refining and regeneration issues of retired transformer insulating oil, we used catalytic hydrogenation to decolorize retired transformer oil. Based on this, polyethylene glycol modified chitosan adsorption process was used to remove corrosive sulfur and heavy metal copper ions, and achieve the regeneration of retired transformer oil. The results show that when the catalytic hydrogenation temperature is 220℃, the reaction pressure is 4 MPa, and the volume ratio of hydrogen to oil is 300∶1, the retired transformer oil can achieve decolorization. The self-made modified chitosan-polyethylene glycol composite adsorbent material (CS-PEG) can quickly remove the corrosive sulfur and metal copper ions from oil samples. After being treated by this process, the retired transformer oil becomes transparent, its acid value decreases to 0.003 mg(KOH)/g, the breakdown voltage reaches 45 kV, and the dielectric loss factor drops below 0.001. This process has good potential for application.