In this paper, we analyzed the basic characteristics of natural ester oil, and introduced the basic research results in electrical structure design and insulating oil processing of a 110 kV oil-immersed transformer using natural ester oil, and then compared with that of mineral insulating oil transformer with the same grade. The application of natural ester insulating oil in power transformers was discussed. The results show that when the natural ester oil is used in transformers with voltage of 110 kV and below, the design principle of electrical structure can refer to mineral insulating oil transformer standard. The impregnation treatment of insulating parts and the selection of sealant pad when using the natural ester insulating oil are quite different from using mineral insulating oil. During the storage and transportation process, natural ester insulating oil should avoid contact with air to prevent oxidation. The kinematic viscosity of natural ester insulating oil has an obvious effect on the temperature rise of transformer, which should be corrected accordingly when designing the structure. On the basis of the excellent properties of natural ester insulating oil, it has broad prospects in power transformer field.

Due to the presence of electric field, water droplets on the surface of hydrophobic coating are prone to generate corona discharge, which will further develop into surface flashover in severe cases. In order to improve the wet flashover voltage of coating, a superhydrophobic coating was prepared by nano-silica modified methyl silicone resin, the adhesion and wear resistance of the coating were tested, and then the flashover voltages of different types of coatings were measured and the surface flashover phenomena were observed. The results show that the adhesion of the superhydrophobic coatings reaches level 0. The coatings still maintain good superhydrophobicity after mechanical wear, and the static contact angle is greater than 155°. The wet flashover voltage of the coating reaches 26.2 kV, which is 42.4% higher than that of the RTV silicone rubber coating. The superhydrophobicity is conducive to the movement of water droplets on coating surface under electric field to create a dry area, therefore the superhydrophobic coating still has good insulating properties in wet environment.

Low glue vacuum pressure immersion (VPI) insulation system has been widely used in the manufacturing of high voltage motor. In this paper, the coil manufacturing process in low glue VPI process was studied, and the effect, value, and improvement possibility of each coil manufacturing process were analyzed. The existing problems and improvement measures of the current process were proposed, and a coil sample was made to conduct properties comparison tests. The results show that there are unnecessary processes that consume time and energy in the traditional coil manufacturing process, which can be improved by changing the shape of winding former and coating pre-coated insulation layer. Compared with the previous coil manufacturing process, the improved coil manufacturing process has the advantages of better coil performance, shorter manufacturing cycle, lower production cost, higher work efficiency, and more environmentally friendly.

A bionic superhydrophobic coating with excellent hydrophobicity and self-cleaning properties was used to prepare insulation surfaces, a DC flashover test of the contaminated insulation surface wetted by fog water was designed to study the DC pollution flashover characteristics of the bionic superhydrophobic insulation surface. At the same time, according to the wetting state of surface droplets, the pollution flashover voltage of the superhydrophobic coating surface was predicted from the perspective of electric field. The results show that the superhydrophobic coating surface exhibits self-cleaning properties during wetting and voltage applying process, and the flashover is formed through surface droplets and dry regions. The flashover voltage predicted by the method in this paper is negatively correlated with the droplet volume and positively correlated with the contact angle, the predicted value is in good agreement with the measured value, and the accuracy is higher than that of the traditional prediction model.

An experimental platform was built to conducted thermal ageing experiments at 105℃, 155℃, and 180℃ respectively for 30 d on a domestic meta-aramid insulating paper, and the changes of chemical structure, micro-morphology, and electrical properties of the paper during thermal ageing process were studied. On the basis of isothermal surface potential decay method, the surface trap distribution characteristics of the samples at different thermal ageing stages were compared, and the polymerization degree and electric strength of the samples under different ageing temperature were fitted. The results show that the thermal ageing has a destructive effect on the surface and cross section of meta-aramid paper macroscopically, resulting in a decrease of the polymerization degree overall. Microscopically, the thermal ageing has a significant destructive effect on the amide bonds, C-N bonds, and C=O bonds in the molecular structure of meta-aramid paper. The thermal ageing causes the volume conductivity of meta-aramid paper to increase and the electrical strength to decrease. During the thermal ageing process, shallow traps will appear briefly and then disappear, and the higher the temperature, the earlier the shallow traps appear, which is of great significance for the quantitative judgment of thermal ageing stage for the meta-aramid paper.

A large number of tests were carried out on XWP2-70 and XP-160 insulators under sunny weather in Wuhan insulator artificial pollution test field, and the dynamic relationship between the first harmonic of leakage current and meteorological factors under different pollution degrees was obtained. The mathematical model of the relationships among the surface salt density of insulators, leakage current, and environment relative temperature under different gray density were established. The relation expression between the first harmonic amplitude of leakage current and the relative humidity under different salt density was predicted by nonlinear regression analysis method, and the quantitative relationship between salt density and the relation expression coefficient was obtained. The results show that the leakage current on insulator surface always reaches the maximum value at 2-6 PM at night, and decreases to the minimum value at 13-17 PM in the day. The overall leakage current curve presents a saddle-shaped curve. The first harmonic of leakage current is positively correlated with humidity and negatively correlated with temperature. Under the same humidity and different temperature, the first harmonics of leakage current are almost the same, but under the same temperature and different humidity, the first harmonics of leakage current change greatly. The leakage current mainly depends on the environment relative humidity, when the relative humidity is higher, the leakage current increases faster with the increase of the relative humidity. Therefore, the influence of humidity should be mainly considered when establishing a pollution prediction model.

Epoxy composites with different orientation degree of nano BN were prepared by applying different DC electric fields during the curing process of BN/epoxy resin mixture, and the influences of different electric field strength on the orientation degree of BN nanosheet were studied, while the influences of orientation degree of BN nanosheet on the thermal conductivity and electrical properties of epoxy composites were discussed. The results show that with the increase of DC electric field strength, the orientation of BN nanosheet is closer to electric field direction, the thermal conductivity of epoxy composites is improved, and the dielectric constant and electrical conductivity increase. By adjusting the distribution and orientation of BN nanosheet, the thermal conductivity and insulating properties of epoxy composite are improved synergistically.

Biaxially oriented polypropylene (BOPP) film is an important part of capacitor. The key parameters (ash content, isotacticity, molecular weight, melt flow rate, isotactic sequence length) of polypropylene resin used as raw materials for BOPP films and their influence rules were summarized in this paper. At the same time, the existing production technology of BOPP capacitor film was summarized, and the methods to improve the performance of BOPP film were further reviewed. Finally, it is proposed that the future development of BOPP films for capacitors will focus on the ultra-low ash resin raw materials and heat resistant films.

An epoxy resin-based sheet molding plastic (E-SMC) was prepared by using multi-function epoxy resin as the resin matrix, dicyandiamide as main curing agent, and mica as fillers. Then the epoxy molding composite was prepared by molding process, and its mechanical properties, thermodynamic properties, and electrical properties were systematically tested and studied. The results show that the epoxy molding composites have high mechanical strength, and the tensile strength, bending strength, vertical compression strength and parallel compression strength of typical samples can reach 64, 178, 440, and 332 MPa, respectively. At the same time, the epoxy molding composites have low density (1.69-1.76 g/cm³), high glass transition temperature (T_g up to 201℃), and excellent electrical strength properties, and the breakdown voltage of typical samples is up to 100 kV, the electric strength can reach 17.1 kV/mm, the comparative tracking index (CTI) is 600 V.

To deeply understand the self-recovery mechanism of electrical tree in silicone rubber (SiR), the self-recovery characteristics of SiR electrical tree were studied in this paper. The morphology variation during the self-recover process of electrical tree in SiR were observed, the elastic modulus and crosslinking density of SiR during the self-recovery process of electrical tree were tested, and the self-recover mechanism of SiR electrical tree was analyzed. The results show that the electrical trees in SiR exhibit self-recovery characteristics without external interventions including external electrical field and healing fillers, wherein some branches of electrical tree gradually degrade and eventually disappear, meanwhile the fractal dimension gradually decreases, and the rate of self-recovery exhibits the stage characteristics of fast at first and then slow. During the self-recovery process, the elastic modulus of SiR sample increases slightly from 0.964 MPa to 0.977 MPa, and the crosslinking density decreases slightly from 1.886×10^-4 mol/g to 1.883×10^-4 mol/g. After recovery, the physical crosslinking density of electrical tree deteriorated area increases slightly from 0.55×10^-4 mol/g to 0.58×10^-4 mol/g. Combined with the growing mechanism of SiR electrical trees, it is analyzed that the self-recovery process of SiR electrical tree is essentially the elastic contraction of tree channel, which is controlled by the gas flow in the channel and accompanied by the reconstruction of hydrogen bond.