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.

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 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.

In order to study the influence of sand covering at the umbrella skirt of porcelain insulator on the surface electric field and potential distribution, a two-dimensional symmetric electrostatic field model of XP-70 porcelain suspension insulator was established based on the finite element method, and the surface electric field and potential distribution of the insulator under different sand covering conditions were analyzed. The results show that the surface electric field of porcelain insulator shows U-shape distribution, and the electric field and potential are affected by the geometry of porcelain insulator and the medium material. There is a local peak of electric field strength at the junction point between the upper and lower surfaces of the umbrella skirt of each insulator and the fittings. When the insulator umbrella skirt surface is covered with sand, there is a weak effect on the its surface potential, but the field strength at the sand cover of umbrella skirt will decrease, and the field strength decrease amplitude of the insulators near the high voltage side and the low voltage side is greater. The decrease amplitude is not related to the sand layer thickness. With the increase of sand layer thickness on insulator surface, the field strength at the junction between the upper surface of each insulator umbrella skirt and the fittings will increase greatly at first and then decrease to a stable value. When there is no sand belt in the sand layer, the field strength at the no sand belt increases, and the increase amplitude is related to the sand layer thickness and the width of no sand belt.

The frequency domain reflection method can effectively detect the fault in cable, but the traditional methods can only locate the fault in cable and can not detect the impedance state of the fault. Therefore, we proposed a cable fault detection method based on the correlation coefficient of reflection coefficient spectrum in this paper. Firstly, the comparison function was designed, then the function curve of correlation coefficient was constructed by comparing the function and reflection coefficient spectrum, and the position and type of the extreme value in the function curve were used to detect the position and impedance state of fault, respectively. At last, a 10 kV power cable with fault was conducted simulation research and a 60 m of 10 kV power cable with fault was conducted experimental research. The simulation and experiment results show that the cable fault detection method based on correlation coefficient of reflection coefficient spectrum has high location accuracy on the cable faults, and it can accurately detect the impedance state of fault.

Aiming at the thermal ageing problem of silicone rubber, a non-linear ultrasonic testing method was introduced to carried out related experimental research. The silicone rubber samples of cable joint were conducted thermal ageing test at 200℃ for different time, and the variation trends of relative non-linear coefficient, micro structure, and surface morphology of the aged samples were tested and analyzed. The results show that with the increase of thermal ageing time, the relative non-linear coefficient of the silicone rubber shows an obvious increasing trend. On the basis of the test results, it is obtained that there is a good linear correlation between the relative non-linear coefficient and the thermal ageing time, and the determination coefficient R² is greater than 0.95. After thermal ageing, the organic content of silicone rubber decreases gradually, the crosslinking degree increases gradually, and the micro defects such as local holes, cracks, and filler precipitation begin to appear on the surface. The microstructure undergoes a certain degree of degradation, which results in the enhancement of ultrasonic non-linear effect.

The anti-pollution flashover coating in a converter station appears rapid hydrophobicity failure phenomenon in a short time after coating, and there is a large domestic winery within 5 kilometers of it, which belongs to a special operating environment. In order to analyze the reasons for the rapid hydrophobicity failure of the anti-pollution flashover coating in this special environment, two groups of anti-pollution flashover coatings were selected and placed in the converter station to conduct simulation tests, and then the hydrophobicity, roughness, and Fourier transform infrared spectroscopy of the two groups of anti-pollution flashover coatings were analyzed in the field and laboratory. The results show that the hydrophobicity of the anti-pollution flashover coating decreases from grade HC1 to grade HC4-HC5 within 7 months. Affected by the surrounding winery environment, the contamination on anti-pollution flashover coating surface in the converter station contains organic substances such as alcohols and phenols, which affects the migration of small molecular siloxanes, leading to the hydrophobicity failure of the anti-pollution flashover coating, while the coating does not show obvious ageing, and its hydrophobicity can be restored immediately after scrubbing the surface dirt.

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.

In this paper, the performance and characteristics of low smoke halogen-free flame retardant cable material was reviewed. The advantage and disadvantage of ethylene-vinyl acetate copolymer (EVA) as the base material was introduced.The types and flame retardant mechanism of halogen-free flame retardant were reviewed. Finally, the development direction of low smoke halogen-free flame retardant cable material was prospected.

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.