The epoxy resin for casting in saturated reactors is prone to ageing and cracking when subjected to electrical stress and mechanical vibration, it is necessary to improve its mechanical and thermal properties on the basis of maintaining its excellent insulating properties and corrosion resistance. In this paper, taking the functional optimization design as principle, a silicon dioxide dielectric layer was formed on the surface of silicon carbide whiskers (SiCw) by heat treatment to obtain SiCw@SiO₂. Then a SiCw@SiO₂/EP composite dielectric was prepared by doping modification, and its dielectric properties, mechanical properties, and thermal properties were tested. The results show that the SiCw@SiO₂/EP composite dielectric has both high dielectric constant and low dielectric loss, and its toughness is also improved. Due to the continuous thermal conductivity network formed by the contact of SiCw, the thermal conductivity of the SiCw@SiO₂/EP composite dielectric increases by 117% than that of pure epoxy resin.

In this paper, BNNS@SiO₂/epoxy composite dielectrics with different filler content were prepared, the chemical characteristics and microscopic morphology of the composite dielectrics interface area were studied, and the trap characteristics and breakdown properties of the composite dielectrics were studied by thermal stimulation depolarization current method and breakdown test. The results show that BNNS@SiO₂ has a core-shell structure and the thickness of the coated SiO₂ is at the nanoscale. There is a clear chemical bonding effect on the surface of BNNS@SiO₂, which can form a strong interface zone with the epoxy matrix, so as to improve its compatibility with the epoxy matrix. A small amount of BNNS@SiO₂ can effectively improve the electric strength of the composite dielectric, and when the mass fraction of BNNS@SiO₂ is 1%, the electric strength of the composite dielectric increases by 52.3%. When the content of BNNS@SiO₂ nanoparticles is small, the deep traps in the epoxy composite dielectric increases. When content of BNNS@SiO₂ nanoparticles is large, the deep traps decrease and the shallow traps increase. In addition, the thermal conductivity of the core-shell structure BNNS@SiO₂/epoxy composite dielectric increases significantly, which is conducive to the heat dissipation of insulation under high electric field. Through the comprehensive effect of deep trap effect and thermal conductivity improvement, the breakdown performance of epoxy composite dielectric is improved significantly.

An ANF/BTNF paper-based composite film was prepared taking aramid nanofiber (ANF) as the high-temperature resistant matrix and filling with barium titanate nanofiber (BTNF). The effect of different BTNF content on the dielectric properties of the composite films was studied. The results show that the thickness of ANF/BTNF composite film is about 10 μm. When the mass fraction of BTNF is 0%-20%, both the dielectric constant and electric strength of the composite films increase with the increase of BTNF content. When mass fraction of BTNF increases to 40%, the dielectric constant of the composite film increases significantly, but decreases rapidly at high-frequency zone, and the dielectric loss factor increases significantly, at the same time, the electric strength of the composite film decreases slightly. Therefore, the ANF/20BTNF composite film with 20% mass fraction of BTNF has the best comprehensive dielectric properties, the dielectric constant at 1 kHz reaches 4.78, and the electric strength is 8.90 kV/mm.

Transformer oil is prone to microbial contamination during storage, utilization, and transportation, which affects the quality and insulating performance of transformer oil. In this study, the effects of temperature and humidity on the microorganism growth in transformer oil were mainly investigated, and the quality changes of transformer oil before and after treatment were analyzed. The functional group structure and organic species of transformer oil were identified, and some effective treatment methods for microbial pollution in transformer oil were proposed. The results show that both the transformer running oil and faulty oil contain bacillus subtilis, bacillus using sugar to produce acid, bacillus using sugar to produce acid and gas, and bacillus producing acid and gas without sugar. The number of microorganisms in faulty oil is much greater than that in running oil, and the number of bacillus subtilis is the largest, while there is no microorganism cultured in new transformer oil. The high temperature could restrict the growth of microorganism in transformer oil. When the temperature is 60℃, the microorganisms will not be completely inactivated, and once the temperature returns to 37℃, they will start to grow and reproduce again. When the mass ratio of oil and water is 99∶1, 49∶1, 19∶1, and 9∶1, four types of bacillus all exist at 37℃, and the number of bacillus increases with the increase of oil-water mass ratio. The regeneration treatment method of high-pressure sterilization+molecular sieve coarse filtration+ultrafiltration can make the contaminated transformer oil clear and transparent, and the microorganisms disappear. The regenerated oil mainly contains O-H, C-H, C=O, and unsaturated bonds. After regeneration treatment, the breakdown voltage and volume resistivity of transformer oil increase from 25.83 kV and 5.70×10¹⁰ Ω·m to 49.50 kV and 4.68×10¹¹ Ω·m, respectively, and the dielectric loss factor decreases from 6.052% to 0.215%, which meet the requirement of DL/T 1419—2015.

Vegetable insulating oil is easy to age in electrical equipment and produce polar small molecule substances such as formic acid, acetic acid, and formaldehyde, which reduces the physicochemical properties and electrical properties of insulating oil and affects the safety operation of equipment. In order to solve the quality deterioration problem of insulating oil, the aged vegetable insulating oil can be purifed by adsorption technology to reduce the polar small molecule impurities generated during ageing. In this paper, a 2-methylimidazole zinc salt (ZIF-8) and alumina (Al₂O₃) composite material was prepared, the ZIF-8/Al₂O₃ composite material was used to adsorb and purify the aged vegetable insulating oi, and the physicochemical properties and electrical properties of the vegetable insulating oil after adsorption and purification were tested. The results show that after adsorption and purification by ZIF-8/Al₂O₃ composite material, the acid value and dielectric loss factor of the vegetable insulating oil decrease significantly, the volume resistivity and initial oxidation temperature increase significantly, and the quality is improved significantly. In addition, the molecular simulation results also show that the adsorption capacity of ZIF-8/Al₂O₃ composite material for polar small molecules in vegetable insulating oil is better than that of Al₂O₃.

Vegetable insulating oil has gained wide attention due to its green and renewable characteristics as well as excellent fire protection properties, while nanoparticles can effectively improve the electrical properties of vegetable insulating oil. In this paper, the effects of nanoparticles on the electrical properties of vegetable insulating oil were summarized from dielectric loss factor and volume resistivity, and the effects of nanoparticle type, concentration, and surface modification on the breakdown properties of vegetable insulating oil were also discussed. Combining with the differences in the effects of nano-modification on the electrical properties of mineral insulating oil and vegetable insulating oil, we summarized the current research difficulties of nano modified vegetable insulating oil, and prospected the research direction and prospects of nano modified vegetable insulating oil.

In order to improve the toughness and oil absorption of wet-processed insulating parts such as insulation molding parts and angle rings, strengthen the process operability in the assembly process, and thus improve the operation reliability of transformer, the performance of the cotton pulp composite insulating paper with different raw material ratio was studied. The cotton pulp ratio of the cotton pulp composite insulating paper was determined, and then the finished product was processed and their performance was tested. The results show that the comprehensive performance of the cotton pulp composite insulating paper with 25% volume fraction of cotton pulp is the best, and the corner ring and insulating parts produced by the cotton pulp composite insulating paper have better flexibility and oil absorption.

The partial discharge ultrasonic signal attenuates severely on power transformer equipment shell, resulting in larger differences in the partial discharge signals received by different positions of sensors, which greatly affects its measurement accuracy and detection efficiency in field application. In this paper, a partition model of oil-immersed power transformer was built using finite element simulation software, the partitioning rule of partial discharge ultrasonic signal on the main surface of oil tank was obtained, and the transformer spatial sound pressure and partition sound pressure distribution maps were formed. On the basis of monitoring point optimization method of Pearson correlation coefficient and K-means clustering, the monitoring points with the best sensitivity of spatial sound pressure and partition sound pressure were preferably selected and compared. The results show that the average detection efficiency of the A-level monitoring points is 86.0%, which realizes the efficient detection of transformer partial discharge and provides a new method for selecting the placement points of ultrasonic sensors.

Methanol is an important characteristic component in the evaluation of oil-paper insulation state of transformer due to its strong stability and high content in the early ageing stage of insulating oil, while water is an indispensable product during the ageing process of oil-paper. In order to clarify the effect of water on the methanol diffusion in vegetable insulating oil, blending models of vegetable insulating oil, water, and methanol with water content of 1.0%, 1.5%, 3.0%, and 5.0% were constructed, and the diffusion trajectory, diffusion coefficient, interaction energy, hydrogen bonding, free volume of the substances in the model were calculated by molecular dynamics method. The mechanism of water promoting methanol diffusion was explained from microscopic perspective. The results show that with the increase of water content, the interaction energy between methanol and vegetable insulating oil decreases, the hydrogen bond stability of the system decreases, and the free volume increases, which ultimately leads to the enhancement of methanol diffusion in vegetable insulating oil.

Aiming at the problems of large specific surface area of conventional flake boron nitride and sharp increase in resin viscosity when compounded with epoxy resin, we prepared spherical boron nitride and used it as a filler to compound with epoxy resin to prepare spherical boron nitride/epoxy composites. The preparation process and curing characteristics of spherical boron nitride/epoxy composites were studied, and the influences of the morphology and filling amount of flake/spherical boron nitride fillers on the mechanical and electrical properties of epoxy resin composites were compared. The results show that with the increase of reaction temperature, the curing degree change curve of epoxy resin shows “S” shape, and the curing process can be roughly divided into three stages of “slow-fast-slow”. In terms of mechanical properties, adding a small amount of boron nitride can improve the mechanical properties of the epoxy resin composites; when the filling amount is high, spherical boron nitride/epoxy composites have better mechanical properties than flake boron nitride/epoxy composites. In terms of electrical properties, the relative dielectric constant of the epoxy resin composites increases with the increase of boron nitride content, and the dielectric loss factor is lower than 0.02; compared with the flake boron nitride/epoxy composites, the spherical boron nitride/epoxy composites have less “filler-resin” interface, lower relative dielectric constant and dielectric loss factor; adding an appropriate amount of boron nitride can significantly improve the volume resistivity and electric strength of composites.