An interturn insulation test platform was constructed, and the voltage-withstand tests were conducted on vegetable insulating oil-paper insulation and mineral insulating oil-paper insulation under lightning impulse voltage, switching impulse voltage, and power frequency voltage. The results show that under power frequency voltage, the breakdown voltage of vegetable oil-paper insulation is higher than that of mineral oil-paper insulation. Under switching impulse voltage, the breakdown voltage of vegetable oil-paper insulation is slightly higher than that of mineral oil-paper insulation. Under negative lightning impulse voltage, the breakdown voltage of vegetable oil-paper insulation is significantly lower than that of mineral oil-paper insulation. Considering the differences in breakdown voltage of interturn insulation with different specification of wires, on the basis of test results, the field strength of mineral oil-paper interturn insulation and vegetable oil-paper interturn insulation were simulated and calculated by finite element method so as to guide the design of interturn insulation for vegetable insulating oil transformer. The simulation results show that the maximum field strength of mineral oil-paper interturn insulation is higher than that of vegetable oil-paper interturn insulation under the breakdown voltage.

In order to study the feasibility of using sapium sebiferum seed oil as the natural ester insulating oil for transformers, sapium sebiferum seed oil was subjected to refining treatments including degumming, deacidification, decolorization, and dehydration, to prepare a sapium sebiferum seed insulating oil. Its physicochemical and electrical properties were compared with those of mineral insulating oil, and accelerated thermal ageing test was carried out on it under 130℃ to study its thermal ageing characteristic. The results show that the main fatty acid component of sapium sebiferum seed insulating oil is polyunsaturated fatty acid, its physicochemical and electrical properties can meet the requirements of relevant standards, and its kinematic viscosity and dielectric loss factor are greater than those of mineral insulating oil, but the ignition point is much higher than that of mineral insulating oil. After thermal ageing at 130℃ for 250 h, 500 h, 750 h, and 1 000 h, the sapium sebiferum seed insulating oil has less color change and higher breakdown voltage than mineral insulating oil, but its increase amplitude of dielectric loss factor is great.

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.

Under the background of “carbon peaking and carbon neutrality” development strategy goal, in order to explore the application prospects of green and environment friendly bio-based epoxy resins in electrical equipment, a bio-based resin of maleopimaric-based epoxy resin (MPAER) was prepared using a renewable resource of rosin as raw material. Taking methylhexahydrophthalic anhydride (MHHPA) as the curing agent, we systematically studied the curing characteristics, as well as the thermal, mechanical, and electrical properties of the MPAER/MHHPA system, and the MPAER/MHHPA system was compared with the DGEBA/MHHPA system composed of commercial diglycidyl ether of bisphenol A (DGEBA). The results show that the MPAER/MHHPA system and DGEBA/MHHPA system have equivalent curing reaction activity. The glass transition temperature of the MPAER/MHHPA system is 112.8℃, its mechanical and electrical properties are slightly weaker than those of the DGEBA/MHHPA system, and its electric strength is 9.4% lower than that of the DGEBA/MHHPA system. However, the comprehensive performance of the MPAER/MHHPA system is still good, and its performance can be further improved by optimizing the structure of MPAER or blending with other types of epoxy resins.

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.

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.

Under high thermal fault, the internal state change and gas production mechanism of insulation system in super/ultra-high voltage transformer is unclear, which seriously restricts the state analysis and diagnosis of transformer. In view of this problem, the generation path of characteristic gas and decomposition mechanism of oil-paper insulation system in super/ultra-high voltage transformer were studied under high thermal fault by enthalpy theory and simulation method. The gas generation mechanism was obtained according to the enthalpy theory, and the gas generation mechanism and path proposed in this paper were verified by simulation. The results show that the chain alkanes in the oil-paper insulation system are more likely to crack than the cycloalkanes and bicyclic aromatic hydrocarbons under high thermal fault. The generation rate of cracking characteristic gas of various materials in descending order is cellulose, chain alkanes, cycloalkanes, and bicyclic aromatic hydrocarbons. According to the gas generation energy, the characteristic gases CH₄ and C₂H₆ are the easiest to generate, while C₂H₂ is the most difficult to generate. The generation rate of characteristic gases in oil-paper insulation system can be used to judge the severity of high thermal fault.

The mechanical properties of insulation pressboard are key factors in modeling the structure of transformer windings. The operating transformer winding is subjected to periodic electromagnetic forces, and the static stress-strain test results cannot characterize the dynamic mechanical properties of insulation pressboard. In this paper, an asymmetric hysteresis model was proposed to study the dynamic mechanical properties of the insulation pressboard under periodic electromagnetic forces, and the model includes not only linear damping and stiffness coefficients, but also nonlinear dynamic stiffness. In the experiment, a pneumatic vibration exciter was used to simulate the amplitude and frequency of the electromagnetic force, and the stress-strain data of the insulation pressboards under different clamping forces was obtained. A multi-objective optimization algorithm based on NSGA-II algorithm was used to train the model parameters. The results show that the stiffness and damping of the insulation pressboard are closely related to the clamping force, and the oil-immersed pressboard has obvious damping characteristics. As the clamping force increases, the dynamic stiffness of the insulation pressboard decreases during the loading and unloading processes. Compared with the amplitude of periodic electromagnetic force, the frequency of periodic electromagnetic force has more significant effect on the mechanical characteristics of insulation pressboard.

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.