In this paper, the research progresses of functional polysiloxane, silane coupling agent, POSS, and other organosilicon modified epoxy resins were reviewed from two aspects of physical and chemical modification. Combined with the development demand of material science, it was proposed that the water-based and photocurable environment-friendly silicone modified epoxy resin would be the future development direction.

In this paper, the reasons for the poor oxidation resistance of natural esters were analyzed from their chemical composition, the currently assessing methods and improving techniques of oxidation stability for natural esters were reviewed, and the advantages and shortcomings of different methods were pointed out, which provides a reference for correctly evaluating the oxidation resistance of natural esters.

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.

A quartz reinforced polyimide resin composite with high wave-transmitting and low thermal conductivity was prepared by the autoclave molding process using a fluorine-containing polyimide resin as resin matrix and quartz fiber cloth as reinforcement. At first, the curing behavior of fluorine-containing polyimide was preliminarily determined by DSC and viscosity-temperature curve. Then the optimal curing process parameters was determined by studying the influences of different curing process parameters on the mechanical properties of the composites. At last, the thermal conductivity, dielectric properties, and wave-transmitting properties in a wide frequency range of the composites were investigated. The results show that during the molding process of polyimide composite, the optimal molding temperature is 300℃, the molding pressure is no less than 1.0 MPa, and the curing temperature is 370-390℃. The polyimide composite prepared according to the optimal molding process parameter has 0.57 W/(m·K) of thermal conductivity in the range of 25-450℃ and excellent dielectric performance in the range of 7-18 GHz, and its transmittance is more than 83%, which meets the application requirements of wave-transmitting functional materials.

In order to evaluate the application of silicone gels in the packaging of IGBT power modules, three domestic silicone gels were selected for comprehensive comparison, including the appearance, density, viscosity, mixing ratio, and gel time before curing and insulating properties, oil penetration, damping, adhesion force, and high temperature resistance at 200℃ after curing. The differences of the three silicone gels were analyzed, and IGBT power module was encapsulated with the three silicone gels, respectively, then the encapsulated modules were conducted the temperature cycle test. The results show that the initial viscosity and mixing ratio of silicone gels have an impact on the packaging process and equipment, and the penetration, insulating properties, oil penetration, damping, and adhesion after curing have a guiding role in the selection of silicone gel, but the high temperature resistance and temperature cycling resistance are the most important indicators to evaluate whether the sample can be applied to the packaging of IGBT power module.

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 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.

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.

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.

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.

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.