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.

Epoxy resin and its composite materials play a major insulation role in electrical apparatus due to their excellent thermodynamic and electrical insulating properties. With the gradual development of electrical apparatus towards high voltage and high power, as well as the continuous rise of voltage levels, the performance requirements for epoxy insulating materials inside electrical apparatus are increasingly increasing. This paper focused on epoxy resin insulating materials for high-voltage electrical apparatus, and reviewed the current research and application progress from three aspects: formulation composition, curing process, and performance improvement of insulation systems. It was aimed to establish the relationship between the composition, structure, and macroscopic properties of epoxy insulation systems, provide suggestions and prospects for the development direction of domestic epoxy resin insulating materials in the future, and accelerate the localization development of epoxy resin materials for high-voltage insulation.

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.

Partial discharge often occurs due to condensation on the surface of insulator inside the switchgear of box-type substation at the bottom of the wind turbine tower, which seriously threatens the operational safety of equipment. In order to further understand the electric field distribution and discharge process on the surface of epoxy resin with condensation, we used artificial spray condensation was to simulate the natural condensation process in this study. The influence of condensation on the electric field distribution of the insulation surface was simulated and analyzed when the electric field non-uniform coefficient was changing. The spectrogram of partial discharge on the epoxy resin surface under different condensation amount was measured, and the change law of the insulation surface discharge was further discussed. The results show that the artificial spray condensation can quantitatively simulate the condensation amount on the insulation surface under natural condensation. Condensation at different locations can cause the distortion of partial electric field, leading to the accumulation and increase of surface charges on the discharge path, which increases the possibility of partial discharge. When the non-uniformity coefficient of surface electric field is larger, the partial discharge initial voltage is lower, and partial discharge is easier to occur. The increase in the adhesion amount of condensation on the insulation surface promotes the partial discharge. With the increase of condensation amount, the degree of surface electric field distortion and the probability of water droplet fusion increase, while the initial discharge voltage decreases, the number and amplitude of surface discharge increase.

In recent years, buffer layer ablation failure occurs frequently in high voltage cables with corrugated aluminum sheathed structure, but there is a lack of effective method to determine the severity of ablation defects in cable buffer layer. In order to explore the evolution law of gas product concentration during buffer layer ablation, and use it to diagnose the severity of ablation defects, a simulated experimental platform for buffer layer ablation was established in this paper. The law of ablative characteristic gas concentration of buffer layer with different water contents changing with ablation time was investigated,and the variation law was quantitatively analyzed by using a negative exponential function n=-Aexp(-t/τ)+n₀. The results show that the concentration of C₂H4, C₂H₆, and H₂ increases in a negative exponential relationship with the increase of ablation time. With the increase of water content, the concentration of C₂H₄ and C₂H₆ decreases slightly, while that of H₂ increases. The generation rate coefficient(A/τ) of C₂H₄ and C₂H₆ can reflect that whether the buffer layer is damp, and the A/τ of H₂ increases gradually with the increase of water content in buffer layer, which is expected to be one of the bases for judging the degree of damp of buffer layer.

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.

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.

Cable joint is a key accessory of high-voltage DC cable, its insulation performance determines the stability of high-voltage DC transmission system. To verify the effectiveness of the charge transport model in calculating the electric field distribution of cable joints, we calculated the mobility of injected charge carriers and the conductivity of ionized charges through blocking experiments, and proposed a charge transport model that simultaneously considered the effects of injected and ionized charges, the undetermined parameters in the transport model were simplified. Then the electric field distribution of the XLPE-EPDM double-layer structure was simulated and calculated by using a simulation model, and the results were compared with the experimental results. The results show that with the increase of electric field intensity, the polarity of charge on the interfacial of the XLPE-EPDM double-layer structure is reversed. The simulation results calculated by the simulation model are in good consistency with the experimental results, which proves the effectiveness of the simulation model.