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 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.

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.

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.

Polyurethane foam adhesive has good expansion filling characteristics, electrical insulation performance, and waterproofness. To achieve its application in filling the inner layer of the cable joint protective shell, at first, we tested the thermal, electrical, and mechanical properties of polyurethane foam adhesive with different foaming ratios. Then, a two-dimensional axisymmetric model of the cable joint was established, and the steady-state temperature field distribution of the cable joint under different filling adhesive conditions was simulated and analyzed. Finally, a physical model of the 110 kV intermediate joint was established, and thermal cycling tests were conducted on cable joints using different filling adhesives. The results show that all the performance test results of polyurethane foam adhesive are good. With the increase of foaming ratio, the thermal conductivity, insulation performance, and mechanical property of the foam adhesive decrease, with a foaming ratio of 3 times, the foam adhesive shows optimal comprehensive performance. The absolute error between the simulated and measured temperature values of various structure inside the joint using different filling adhesives are basically no more than 10%, which verifies the effectiveness of the simulation model. The steady-state temperature distribution of the joint filled with foam adhesive is similar to that of the joint filled with traditional waterproof adhesive.

This paper reviewed the research progress on active esters for epoxy curing at home and abroad in recent years, with a focus on the structures of different active esters. By classifying active esters according to raw material sources and ester bond positions, the characteristics and differences of active esters with different structures in epoxy resin curing agents were explored. Finally, the development trend and application prospects of active esters for epoxy curing were discussed.

Due to its advantages of high flash point, high ignition point, and biodegradability, natural ester insulating oil is gradually being promoted and applied in high voltage level power transformers. In order to provide basic data support for the insulation structure design of high voltage and large capacity natural ester transformer, we took mineral oil as a reference, and selected natural ester insulating oil as the test object to analyze its breakdown characteristics and gas generation law under lightning impulse voltage. The results show that the lightning impulse breakdown voltage of natural ester turn-to-turn insulation is above 200 kV, with the increase of turn-to-turn insulation thickness and insulation gap distance, it shows an upward trend and is slightly lower than the breakdown voltage of mineral oil under the same conditions. H₂ and C₂H₂ dissolved in oil are the main characteristic gases under lightning impulse voltage, and their relative percentage content increases with the increase of insulation gap. The Duval pentagon method is used for fault diagnosis of dissolved gases in oil, and the discharge at the fault points are basically diagnosed as high-energy discharge, which are consistent with the energy released by lightning impulse.

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.

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 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.