The main insulation of cross-linked polyethylene (XLPE) HVDC cable was sliced at radial inner, middle, and outer layers to as samples, and their equivalent thermal history was modeled by differential scanning calorimetry (DSC). The changes of chemical and electrical properties of each layer in cable insulation after type test were analyzed by infrared spectroscopy (FTIR), space charge, and DC electrical strength test. The results show that after type test, the equivalent heat treatment temperatures of each layer in cable main insulation are about 70℃, there is a small difference between the equivalent heat treatment time of the middle layer and the outer layer, while the equivalent heat treatment time of the inner layer is about 581 times bigger than that of the middle layer. There are little changes in DC electric strength and chemical properties of each layer in cable main insulation. Due to the equivalent heat treatment time of each layer is different, the impurities, polar small molecules, and other substances in inner insulation layer continue to diffuse from the inner layer to the middle layer, which results in the significant accumulation of heteropolar space charges.

The electric multiple unit roof insulators with different operating years were selected as research objects, and the hydrophobic analysis (contact angle method), Fourier infrared analysis, and scanning electron microscope analysis were conducted on them, respectively. The results show that with the increase of service time, the hydrophobicity of the insulator decreases rapidly, while the decreasing trend slows down year by year, and the hydrophobicity of the top umbrella skirt is generally lower than that of the middle and bottom umbrella skirts, which is consistent with the change trend of Si-CH₃ content in insulator analyzed by FTIR. With the increase of service time, the surface morphology of the insulator changes significantly. The micromorphology of the electric multiple unit roof insulator serviced for 6 years is similar to that of the insulator serviced in 110 kV transmission grid for 15‒19 years, which is one of the important reasons that the hydrophobic ageing speed of electric multiple unit insulator is faster than that of transmission grid insulators.

ZnO varistors doped by Al₂O₃ were prepared under different sintering temperatures, and their microstructure and electrical characteristics were studied by scanning electron microscope, X-ray diffraction, current-voltage test, and capacitance-voltage test. The results show that with the increase of sintering temperature, the leakage current of the ZnO varistor doped by Al₂O₃ was suppressed significantly, this is due to the continuous increase of donor degree and interface state density increases the barrier height of grain boundary. With the increase of sintering temperature, Al³⁺ will continuously dissolve into the ZnO grains, the grain resistivity would reduce, and the residual voltage ratio of the ZnO varistor when a large current is passed decreases. When the sintering temperature is 1150℃, the electrical properties of the ZnO varistor are the best, the voltage gradient is 418.7 V/mm, the leakage current is 0.74, the residual voltage ratio is 1.68, and the nonlinear coefficient is 67.5, which is contribute to improve the protective performance of ZnO arrester and limit the overvoltage of the power system, especially the UHV system deeply.

Compared with mineral insulating oil, natural ester insulating oil has the advantages of high biodegradability, non-toxicity, and strong fire resistance, which has the potential to replace mineral insulating oil in power transformer. A set of lightning impulse discharge characteristics test system including high-speed image acquisition system, test power supply, and electrical signal measurement system was established. The positive and negative lightning impulse discharge characteristics of palm insulating oil and mineral insulating oil were tested, and the stop length, development velocity, and gap breakdown characteristics of the streamer in two oils under positive and negative lightning impulse were compared and analyzed. The results show that under the same applied voltage and polarity, the streamer stop length in palm insulating oil is longer and the streamer development velocity is faster compared with the mineral insulating oil. The contents of vitamin A and vitamin E in palm insulating oil have no effect on the streamer stop length, development velocity, and breakdown voltage. The differences of streamer development characteristics and breakdown characteristics under positive and negative voltages mainly comes from the influence of space charge in insulating oil on the streamer development process.

In order to obtain the influence of orientation angle of two-dimensional microsheet on the growth characteristics of electrical tree in composite dielectrics, on the basis of WZ breakdown model of fractal media, we studied the growth and fractal dimension characteristics of electrical tree under different microsheet orientation angles, growth probability index, and discharge threshold voltage. The change of electric field caused by the change of two-dimensional microsheet orientation angle was analyzed, and the influence mechanism of microsheet on the growth of electrical tree was explained. The results show that when the microsheet is oriented perpendicular to the electric field, the electrical tree has the largest fractal dimension and is most difficult to breakdown. With the decrease of the angle formed by microsheet and electric field direction, both the fractal dimension and breakdown time of electrical tree decrease. With the increase of the growth probability index or threshold voltage, the fractal dimension of electrical tree decreases, and the influence on the electrical tree fractal dimension in microcomposite dielectrics with different orientation angles increases. When the orientation angle of microsheet is perpendicular to the electric field, the electric field distribution is relatively uniform. With the increase of microsheet orientation angle, the electric field concentrates at the both ends of microsheet, and the closer the adjacent microsheet, the more concentration the electric field.

A monitoring method for the operating state characteristics of bushing in UHV converter valve hall was proposed from the perspective of intelligent image processing and three-dimensional modeling technology. This method mainly included using intelligent image processing technology to identify and classify the databases of infrared thermal imager and ultraviolet imager, using Kalman filtering technology to realize on-line measurement in real time for the insulation distance of typical metal fittings, and using three-dimensional modeling technology based on finite element method to build the electric field simulation model of typical main equipment bushing in valve hall, and the electric field distribution on the surface of key metal fittings was obtained. Combined with the image database information, insulation distance information, and electric field distribution information of typical main equipment bushing, its operation state parameters were obtained effectively, and its operation state was evaluated by the intelligent algorithm automatically. The results show that when the Kalman filtering technology is not used, the prediction deviation of the distance at key positions changes severely in 0‒160 s. After using the Kalman filtering technology, the jump amplitude of prediction deviation decreases and is basically controlled at the same error level. The neural network has good learning effect, the fitness function tends to be stable after 100 iterations, and the local weight of fuzzy neural network shows typical nonlinear characteristics. The research conclusion can explore potential hidden dangers and locate positive faults effectively, which provide effective data support and protection strategies for the operation and maintenance of main equipment bushing.

Insulating paper is an important insulating material that produced by papermaking technology and widely used in electrical equipment such as transformers, capacitors, motors, wires and cables. According to its composition, insulating paper can be divided into cellulose paper and non-cellulose paper. With the sustainable development of China’s power industry, motors and other electric equipment are gradually getting more efficient and smaller. Therefore, higher property requirements are put forward to insulating paper, especially high-temperature resistant performance. Although cellulose papers have a long history, their heat resistance is not high enough to meet the operating requirements of electrical insulation systems, which need the thermal class of F or above. Non-cellulose papers with higher heat resistance have sprung up. This article briefly introduces the development history, performance characteristics, main uses, production status, and development trends of various high-temperature resistant non-cellulose insulating papers in China.

The physical process of initiation and development of surface flashover in oil-paper insulation of transformer is complicated, and the discharge mechanism remains unclear. In this paper, through experimental measurement and numerical simulation of the needle-plate electrode model for oil gap discharge and the needle-plate electrode model for oil-paper insulation surface flashover, the discharge characteristics and discharge mechanism of oil gap discharge and oil-paper insulation surface flashover under different thickness of paperboard and different surface distance were obtained and analyzed. The results show that under DC voltage, oil-paper insulation surface flashover voltage is lower than the breakdown voltage of oil gap, this is because the paperboard not only changes the distribution of electric field, increases the parallel electric field component at the needle tip, and decreases the initial voltage of the streamer discharge, but also hinders the spread of space charge, enhances the distortion of electric field, and increases the development speed of streamer. In addition, due to the presence of paperboard, the initiation process of streamer in oil-paper insulation surface flashover discharge is completely different from that of oil gap discharge, that the streamer gradually propagates from the tip to the oil-paper interface. Increasing the thickness of paperboard can increase the parallel component of the electric field at the tip, decrease the initial voltage of the discharge, decrease the development speed of the streamer and reduce the surface flashover voltage. The surface flashover voltage of oil-paper insulation increases with the increase of the surface distance, but its nonlinear variation is due to the effect of applied voltage weakens gradually and the effect of space charge distortion electric field is dominant in the process of the streamer developing to the self-supporting discharge stage.

In this paper, the withstand voltage characteristics of cross-linked polyethylene (XLPE) and its nanocomposites at different temperatures was systematically measured by step voltage rising method. A new method for calculating the key parameters of the Crine model was proposed, and the activation energy and charge acceleration distance of XLPE and its nanocomposites at different temperatures were calculated on the basis of the experimental results of step voltage rising method. The results show that the characteristic breakdown time of both the materials decreases with the increase of temperature. At the same temperature and time step, the characteristic breakdown voltage and breakdown time of XLPE nanocomposites are higher than that of XLPE, and the electrical ageing life of XLPE nanocomposites is longer than that of XLPE under high voltage. With the increase of temperature, the ageing activation energy and charge acceleration distance of the two materials increase. Under the same temperature, both the ageing activation energy and charge acceleration distance of XLPE nanocomposite are smaller than that of XLPE. It is more intuitive to reflect the ageing resistance of insulating materials by activation energy and charge acceleration distance on basis of Crine model than the ageing life index on basis of the inverse power model or exponential model.

To improve the UV resistance of room temperature vulcanized silicone rubber (RTV), we used titanate coupling agent (PN) to modify nano zinc oxide (ZnO), and then nano ZnO-RTV composites were prepared by doping different mass fraction of modified nano ZnO into RTV. The ultraviolet accelerated ageing experiments were conducted on pure RTV and nano ZnO-RTV composites, and the effect of nano ZnO on the ultraviolet resistance of RTV was compared and analyzed. The results show that nano ZnO can effectively improve the UV shielding performance of RTV, and the UV shielding rate of nano ZnO-RTV composite with 1.0% of ZnO can increase by 72.63%; after adding nano ZnO, the electrical strength of RTV is slightly improved. After UV ageing for 2 500 hours, the decreasing amplitude of static con-tact angle and the ageing degree which reflected by surface micro-morphology of pure RTV are far greater than that of nano ZnO-RTV composite, it is verified by the changes of Si-(CH₃)₂, Si-CH₃, and C=O of RTV molecular chains before and after ageing. At the same time, after UV ageing for 2500 hours, the thermal stability of nano ZnO-RTV composite is significantly better than that of pure RTV.