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 the process of transportation and laying, the submarine cable will inevitably be twisted. If the twisting angle is too large, it will cause irreparable damage for the submarine cable. In this paper, a torsion model of submarine cable was established by finite element method, and the characteristic parameters that can effectively reflect the mechanical characteristics of submarine cable were determined by analyzing the temporal and spatial distribution characteristics of stress and strain. The threshold values of each characteristic parameter when torsion failure occured were established, and the mechanical parameter system that can represent the torsion behavior of submarine cable was established. The results show that the axial stress distribution of the submarine cable is more uniform at the initial stage of torsion. With the increase of torsion angle, the axial stress distribution of cable body will fluctuate. A parametric system including copper conductor stress, XLPE insulating layer stress, lead alloy stress, armor layer stress, and torsion angle can be established for parametric evaluation of submarine cable torsion behavior.

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.

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 solve the problem of interface breakdown and surface discharge caused by uneven distribution of electric field of power cable and its terminal insulation, the structural parameters of 35 kV cold shrinkable power cable terminal were optimized to improve its insulation level in this paper. Firstly, the influence of axial length and end radius of stress cone on the terminal electric field distribution was analyzed based on COMSOL simulation software, and the optimal combination of terminal structural parameters was obtained. Then the power cable terminal samples were prepared, and the performance indexes were verified by power frequency AC voltage resistance and partial discharge tests. The results show that the axial length of the power cable terminal stress cone is the main factor affecting the change and distribution of interfacial electric field, and the change of terminal radius has little effect on the terminal electric field. The increase of axial length of stress cone alleviates the interfacial electric field intensity, but it is easy to cause discharge along the surface. The optimal axial length and upper radius of stress cone are 25 mm and 2.5 mm, respectively.

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.

Defects will occur during production and operation of insulator, which will cause the accumulation of surface charge, and affect the distribution of electric field of insulators. In serious cases, surface flashover will occur, and then affect the operation safety of electrical equipment. Therefore, it is of great significance to study the nondestructive testing and evaluation methods of defects in insulators. Firstly, this paper summarized the influence of insulator defect types such as bubble, crack, and metallic foreign matter on insulator insulation performance, and analyzed the generation and development mechanism of different defects. Then, the testing principle and research status of new nondestructive testing methods based on acoustic, optical, and thermal characteristics were summarized and introduced. Finally, the detection methods were comprehensively evaluated from the perspectives of speed and accuracy, the detection effects of different detection methods on insulator defects were evaluated, and the research direction of insulator defect detection in the future were prospected.

In order to improve the ageing resistance of insulating paper in oil-immersed transformer, three kinds of common silane coupling agents were selected to modify the insulating papers by immersing. The obtained samples were subjected to the combined thermal ageing test of oil paper at 130℃ for 35 days, and the tensile strength, permittivity, and breakdown voltage of the insulating papers were measured periodically. The results show that all the three kinds of silane coupling agents can improve the ageing resistance of insulating paper, the insulating paper modified by 3-aminopropyltriethoxysilane almost maintains the original three-dimensional network structure of cellulose during the thermal ageing process, and it exhibits the optimal mechanical strength, dielectric properties, and breakdown resistance.

Under high voltage DC electric field, the particles and defects on the surface of epoxy resin will distort the local electric field and form a non-uniform electric field, and that will induce surface flashover. Most of the existing epoxy resin surface modification schemes focus on the uninformity of treatment, which has limited improvement on the voltage resistance under non-uniform electric field. In this paper, a simulation study was carried out on non-uniform electric field, and the gradient modification scheme was designed according to the characteristics of the electric field. The plasma fluorination modification technology was combined with the concept of gradient insulation, and the plasma step gradient fluorination modification of epoxy resin was realized on the basis of traditional fluorination modification. The results show that the surface morphology, chemical composition, and electrical properties of epoxy resin exhibit a step gradient distribution after plasma step gradient fluorination. Moreover, plasma step gradient fluorination can not only reduce the maximum surface field strength of epoxy resin, but also regulate the dynamic behavior of interface charge, and greatly improve the surface flashover performance of epoxy resin, the improvement effect is better than that of plasma uniform fluorination.

In order to study the influence of the relative dielectric constant of motor insulation structure on the electric field distribution at different frequencies, this article took the relative dielectric constant of a main insulation structure at different frequencies as a variable to calculate its influence on the electric field distribution of the main insulation sandwich structure in the slot and the notch. At the same time, the optimization measures for the electric field of slot were analyzed. The results show that in the sandwich structure of main insulaton, because the film has a lower dielectric constant, it bears a larger electric field than mica tape. When the relative dielectric constant of the air at the notch is constant, the electric field strength of the air at the notch decreases slightly with the decrease of the relative dielectric constant of the main insulation. The insulating paint in the small gap at the chamfer of the notch iron core can reduce the electric field strength of air; without insulatin paint, the small gap generated by chamfer can produce a larger electric field strength of air. Vacuum potting of the notch can effectively reduce the electric field strength of air at the notch.