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 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.

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.

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.

In recent years, with the rapid development of new energy vehicles and flexible direct current transmission projects, and other fields, there was an increasing demand for the metallized film capacitors with high volume ratio and high temperature resistance. Especially under extreme conditions such as high temperature and high electric field, higher requirements were put forward for the electrical performance of dielectric films in capacitors. In this paper, the current research status and development trend of dielectric film materials for metallized film capacitors in recent years were summarized. Firstly, the key factors affecting the energy storage performance of dielectric films were introduced and the failure reasons of metallized film capacitors under operating conditions were analyzed. Secondly, the modification methods of energy storage performance for dielectric films designed on the basis of four aspects, such as molecular chain structure, aggregation state structure, doping of functional fillers, and surface modification were summarized. Finally, the strategies to improve the energy storage performance of dielectric films of metallized film capacitors were summarized and prospected.

The one-dimensional ANF and two-dimensional edge-hydroxylated BNNS (BNNS-OH) were mixed to prepare ANF/BNNS-OH composite insulating papers with “brick -mud” structure by vacuum filtration technology. The mechanical properties, thermal conductivity, dielectric properties, and breakdown properties of the composite insulating paper were studied. The results show that the BNNS-OH arranges in ANF orderly, and the structure is dense. The ANF/BNNS-OH composite insulating paper has excellent mechanical properties, thermal conductivity, and breakdown properties. When the mass fraction of BNNS-OH is 10%, the tensile strength and electric strength of the composite insulating paper are 242.4 MPa and 312.9 kV/mm, respectively. When the mass fraction of BNNS-OH is 40%, the thermal conductivity of the composite insulating paper reaches 6.76 W/(m·K), which is 158.02% higher than that of pure ANF insulating paper. At same time, the composite insulating paper has excellent high temperature wideband dielectric stability.

A high heat resistant o-allylphenol-dicyclopentadiene epoxy resin was synthesized using dicyclopentadiene, o-allylphenol, and epichlorohydrin as raw materials, and its structure was characterized by infrared spectrum and gel chromatography. Then the epoxy resin was cured with bisphenol-A phenolic resin, benzoxazine resin, and active ester respectively, and a PCB substrate was pressed. The curing behavior of the system was studied by differential scanning calorimetry and thermogravimetric analysis. The mechanical properties, dielectric properties, and water absorption properties of the PCB substrate were tested, and compared with the curing system of phenol-dicyclopentadiene epoxy resin. The results show that compared with phenol-dicyclopentadiene epoxy resin, the o-allylphenol-dicyclopentadiene epoxy resin has higher heat resistance (glass transition temperature T_g and 5% thermogravimetric temperature T_d5% are higher), bending strength, impact strength, high temperature bending strength retention, and better dielectric properties, lower water absorption.

To address the issues of inadequate high-temperature insulation performance and thermal stability of wires, a high-temperature resistant ceramic coating was prepared using the nano alumina and a small quantity of nano silica as the primary raw materials by nanoparticle surface modification technology, then the ceramic coating was coated on quartz fiber braided layer to prepare a high-temperature composite insulating material. The structure, composition, and thermal stability of the coating were analyzed by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), and thermogravimetric-differential scanning calorimetry (TG-DSC). The morphology, volume resistivity, and electric strength of the high-temperature resistant ceramic coating-quartz fiber composite insulation layer before and after calcination were analyzed by scanning electron microscopy (SEM), high insulation resistance tester, and automatic voltage tester. The results show that the ceramic coating forms a ceramic protective layer on the quartz fiber braided layer after high temperature calcination, which can enhance the temperature resistance rating of the quartz fiber and improve its insulation performance. When the temperature exceeds 800℃, the insulation resistivity of the high-temperature resistant composite insulation layer still exceeds 2×10⁶ Ω·m, and the average electric strength at room temperature is as high as 400 kV/m, which has certain application prospects in the wires on specialized equipments such as aerospace engines, excitation coils, transformers.

An ANF/mica composite insulating paper was prepared by vacuum assisted filtration and hot pressing technology taking aramide nanofiber (ANF) as matrix and natural mica (mica) as filler. The microscopic morphology, tensile strength, electrical insulation properties, and temperature resistance of the composite insulating paper were studied systematically. The results show that the mica and ANF are superimposed in order during vacuum filtration process, and the mica fragments fill the gaps in paper effectively, creating a dense "brick-and-mortar structure", which significantly enhances the electric strength and insulating properties of the composite insulating paper. Furthermore, the glass transition temperatures of pure ANF insulating paper and ANF/mica-10 composite insulating paper are higher than 300℃, exhibiting excellent thermal stability. Although the addition of mica slightly reduces the tensile properties of pure ANF insulating paper, its insulation strength and tensile performance remain superior to traditional mica paper.