The characteristics and research methods of transformer interturn breakdown, detection and protection and characteristics of interturn fault were introduced in this paper, and the research direction of transformer interturn fault was prospected, which can provide reference for the academic research and operation and maintenance of transformer interturn fault.

In order to study the effect of mesoscale crystal morphology of XLPE material on its AC breakdown characteristics and analyze its mechanism, XLPE samples with different crystal morphologies were prepared by controlling the cooling rate of samples during cooling crystallization. At the same time, the crystalline structure and morphology of the samples were characterized and observed by scanning electron microscope (SEM) and X-ray diffraction (XRD), and its dielectric properties were tested by the broadband dielectric spectrometer, three electrode system, and AC breakdown system. Finally, the test results were verified and the mechanism was analyzed by means of simulation. The results show that decreasing the cooling rate can prolong the crystallization time, making the molecular chains regularly arrange and stack to form large-size spherulites with a relatively high crystal area and relatively perfect structure. The improvement of crystal structure makes the relative dielectric constant of the XLPE sample increase slightly, the conductivity decrease, and the breakdown strength and stability significantly improve. The simulation results are consistent with the test results. The perfect crystal morphology of the sample at mesoscale reduces the degree of electric field distortion between spherulites and inhibits the occurrence of partial discharge and breakdown.

A halogen-free flame retardant unsaturated polyester insulating impregnating resin was prepared by introducing DOPO into unsaturated polyester. The effect of adding flame retardant on the properties of the resin were analyzed by infrared spectroscopy, thermogravimetric analysis and flame retardancy experiment. The results show that the addition conversion rate of DOPO can be improved by using methyl tetrahydrophthalic anhydride (MTHPA) as the carrier to react with DOPO first and then with maleic anhydride (MA). The prepared resin is uniform, transparent after curing, and has good flame retardance, which can reach UL94 V0 level. With the increase of phosphorus content, the thermal stability of resin decreases, and the optimal phosphorus content is about 2.7%. When the molar ratio of unsaturated acid to saturated acid is 1∶1 to 1.5∶1 and using the compound initiation polymerization system, the resin has good reactivity and storage stability.

To investigate the possibility of using black shale as a filler in the plastic industry, the composition and morphology of black shale in Guilin area were studied. It was found that black shale has nano layered structure, and was mainly composed of silica, K-feldspar, and organic carbon. The black shale/HDPE composite were prepared by modifying black shale with different coupling agents and surfactants, and their mechanical properties, morphology, volume resistivity, and dielectric constant were studied. The results show that aluminate coupling agent and sodium dodecylbenzene sulfonate can improve the compatibility between shale and HDPE. When the shale filling amount is 50 phr, the tensile strength, impact strength, and volume resistivity of black shale/HDPE composite reduce. The tensile strength remains at 23.47 MPa, the maximum impact strength is 6.39 kJ/m², and the volume resistivity can also be maintained above 10¹⁴ Ω·cm, maintaining good mechanical properties and insulating properties.

In order to guide the selection of fluorocarbon resin film forming material cured at room temperature in the development of anti-pollution flashover coating, the structure and properties of fluorocarbon resin film forming materials were characterized by FT-IR, AFM, UV ageing, thermogravimetric analysis, contact angle test, volume resistivity and high-voltage capacitor bridge. The results show that the optimal mass fraction of curing agent for FEVE-based type I and type II fluorocarbon resins are 19% and 24%, respectively. Under the optimal curing agent content, the contact angle of FEVE-based type I and type II fluorocarbon resins are 91° and 104°, respectively. After UV ageing for 800 h, the appearance color, hydrophobicity, hardness, adhesion, thermal decomposition temperature, and molecular structure do not change. After 30 min of ultrasonic fog wetting, the AC wet lightning voltage of fluorocarbon resin is about 25 kV, indicating that the FEVE-based fluorocarbon resin has excellent electrical insulation properties and ageing resistance, and is a good base material for the development of antifouling flashover coatings.

A thermochromic microcapsule epoxy resin composite insulation material (TEP) was prepared, and its power frequency permittivity (ε_r), dielectric loss factor (tanδ), and DC conductivity (σ) were analyzed in this paper. The results show that the temperature characteristic of dielectric constant of composite insulation material has an infelction point at 70℃. When the temperature is lower than 70℃, εr increases rapidly with the increase of temperature. When the temperature is higher than 70℃, the change rate of εr with temperature decreases significantly. The tanδ decreases significantly when the temperature is 50-70℃. The addition of thermochromic microcapsules can effectively reduce the DC conductivity of composite insulation material. In the thermochromic temperature range of 50-70℃, the solid-liquid phase transition occurs inside thermochromic microcapsules, which is the main reason for the special temperature characteristics of ε_r and tanδ. In the solid-liquid phase transition process, the molecular activity of the core material in microcapsule increases gradually, and the resistance that it needs to overcome in the orientation polarization with the external electric field decreases, resulting in the rapidly increase of ε_r and the significant decrease of tanδ with the increase of temperature. When the core materials of microcapsule are fully transformed to liquid state, its molecular activity decreases with temperature, leading to the significant decrease of ε_r with temperature.

In order to study the effect of antioxidant types in transformer oil on the thermal ageing performance of insulating paper, antioxidants T501, T531, and DBP were added to the insulation system composed of naphthenic mineral oil and insulating paper, and the antioxidant mass fraction was 0.4%. The heat ageing test was carried out at 130℃ for 600 h. The moisture and furfural content in the insulating oil, the moisture content and polymerization degree in the insulating paper were determined every 120 h. At the same time, the aged insulating paper was characterized by FTIR, XRD, SEM, and EDS. The results show that the addition of antioxidant T501 and T531 have little effect on the deterioration of insulating paper, and the deterioration of insulating paper in the oil with antioxidant DBP is aggravate in the late ageing stage. Since the antioxidant T531 has a combination of neutralization and hydrolysis, it inhibits the degradation process of cellulose, and the ageing degree of T351 insulating paper is the lightest.

In order to study the influence of humid environment on the insulating performance of traction motor stator, we took the newly manufactured and overhauled stator winding of traction motor with silicone insulation system as the research object. The damp heat tests were carried out on the stator winding and its end, the insulating performance of the insulation system before and after moisture absorption were tested, and the main ways of moisture penetration into the insulation system were analyzed. The results show that the insulation resistance of the stator winding insulation system decreases after the damp heat test. The weakest part in the wet environment is the connection welding part of the end winding insulation, which is the main way of moisture to penetrate into the insulation system. Once this moisture channel is formed, it is easy to dry, but in the humid environment, the moisture will enter the channel and cause the insulation resistance decrease. After long term operation, the insulation performance of stator winding will decrease due to humidity.

The nanomolecular model of TiO₂/vegetable oil interface structures before and after modification of two silane coupling agents (KH570 and KH792) were established by molecular dynamics simulation, and the effect of TiO₂ interface before and after modification with silane coupling agents on the diffusion behavior of water molecules in oil were further investigated by dynamics simulation. The results show that compared with the untreated TiO₂, the modified TiO₂ interface has stronger adsorption of water molecules, which inhibits the migration behavior of water molecules in the oil, resulting in the significant reduction of their diffusion coefficient, thus reducing the formation of “small bridges” of water molecule impurities in the oil, and improving the insulating properties of vegetable insulating oil. Among them, the modification effect of KH792 is more significant. Further, by calculating the interaction energy between water molecules and TiO₂ interface system, the number of hydrogen bonds form and the free volume fraction, the causes and physical mechanisms of above phenomena are explain, which provides theoretical support for the study of nanoparticle doping to improve the insulating properties of vegetable insulating oil.

In this paper, the effect of electrical parameters of the semi-conductive layer on the surface electric field distribution of post insulator used in substation was calculated and analyzed by COMSOL. The results show that the semi-conductive layer can weaken the maximum electric field caused by water droplets, wet pollution, and dry pollution to different degrees, and the wet pollution is the most significant, with the electric field decreasing amplitude of 41.58%. Coating semi-conductive layer at the high voltage terminal has a significant improvement effect on the electric field, and the maximum decreasing amplitude of surface maximum electric field is 14.5% compared with not coating semi-conductive layer. When the high and low voltage terminals are coated by semi-conductive layer with the best relative dielectric constant, the comprehensive balance of electric field improvement is better. In the normal range of porcelain electrical parameters, the optimal electrical parameters of semi-conductive layer are universal, the relative dielectric constant of the optimal semi-conductive layer at high voltage terminal is 22, and the relative dielectric constant of that at low voltage terminal is 12. In addition, the resistivity of the semi-conductive layer at high and low voltage terminals should be at least greater than 1×10⁷ Ω·m and 6×10⁷ Ω·m, respectively, and the maximum electric field will be less than the case without semi-conductive layer.