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.

In this paper, the key role of 60 kV θ-pinch coil insulation of field-reversed plasma device in equipment operation was introduced briefly. Combined with operating conditions, the selecting processes of key parameters and manufacturing process of θ-pinch coil insulation were expounded, and its mechanical properties and insulating properties were tested and analyzed. On the basis of the sample analysis, the corresponding prototype was made to test and analyze. The results show that the field strength of the coil corner can decrease by 41% through optimizing the main insulation thickness reasonably and increasing the insulation fillet properly, making the service life of coil prolong by 9 times, and the breakdown voltage is 20% higher than the design voltage. Compared the ANSYS calculating results with the sample test results, it is found that selecting 8 MPa pressure during impregnation curing can effectively enhance the adhesion. The research results provide ideas for the insulation structure design of 60 kV θ-pinch coil of field-reversed plasma device.

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.

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.

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.

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.

In order to reveal the ageing characteristics of metallized film capacitor under ultra-high DC field, the capacitor and its dielectric material were studied. On the basis of the practical working conditions of capacitor, the special designed capacitor elements were conducted ageing tests at 60℃ under the DC field of 0E_n, 1.4E_n, 1.5E_n, and 1.6E_n, respectively. The capacity of the capacitor elements during ageing and the base film (biaxially oriented polypropylene (BOPP) film) after ageing failure were tested. The results show that the failure mechanism of the capacitor is related to the ageing electric field, and there is an electric field threshold. When the ageing electric field is lower than the electric field threshold, the capacitor will go through a long-term failure, and its capacitance decreases affected by the performance degradation of film, the electrical strength of the film decreases with the decrease of the activation energy of molecular segment motion. When the ageing electric field is higher than the electric field threshold, the capacitor will go through a short-term failure, and the extremely high electrical stress causes the original weakness to break down rapidly, the self-healing area increases rapidly, so the equipment life is greatly shortened.

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.

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.