In order to explore the change law of Shore A hardness and surface roughness of silicone rubber and fluorosilicone rubber under continuous low temperature environment, we put the test pieces made of the two raw materials into the low temperature test box, and carried out low temperature ageing test at -50℃ for 0, 48, 96, 144 h, respectively. The change law of Shore A hardness, surface roughness, and surface morphology with low temperature ageing time were studied, and then its principle was analyzed. The results show that at the constant low temperature environment of -50℃, when the ageing time increase from 0 h to 144 h, the Shore A hardness of the two materials increases slowly at first, then increases sharply, and finally decreases slowly. The surface roughness of the two material decreases at first, then increases sharply, and finally increases slowly. Throughout the ageing process, both the Shore A hardness and surface roughness of fluorosilicone rubber are smaller than that of silicone rubber. It shows that under low temperature environment, fluorosilicone rubber is more stable than silicone rubber.

A series of thermal insulating EPG composite with high performance and light wight were prepared through solvent-free BMC thermocompression technique using multifunctional group epoxy resin (MF4101) as matrix, methyl tetrahydrophthalic anhydride as curing agent, and hollow glass beads with high strength as filler and thermal insulating phase. And the structure, mechanical properties, and thermal properties of the composite were studied. The results show that the average particle size of hollow glass beads is 25.6 μm, and it remains intact in the composite. When the amount of hollow glass beads is 80, 120, and 140 phr, the density of EPG composite is 0.82, 0.72, and 0.71 g/cm³, respectively; the compressive strength is 105.7, 68.1, and 67.4 MPa, respectively; the thermal conductivity is low, the value is 0.012 9, 0.085 4, and 0.0826 W/(m·K), respectively. Besides, with high glass transition temperatures and epitaxial degradation temperatures (>300℃), the EGP composite material can be used under high temperature and high pressure for a long time.

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.

A high resistance insulating layer for edge protection of carbon-ceramic linear resistors was prepared using SiO₂-Al₂O₃-B₂O₃ ternary glass as matrix and mullite as filler. The adaptability of expansion coefficient between high resistance insulating layer and resistance ceramic was studied, and the voltage shock resistance was tested using impulse voltage of 1.2/50 μs. The results show that the glass content affects the expansion coefficient, porosity, and electric strength of the high resistance insulating layer. When the glass content in the high resistance insulating layer is more than 80%, the electric strength of the resistance shows a significant downward trend. With the increase of the coating thickness of the high resistance insulating layer, the electric strength of the carbon-ceramic linear resistance increases obviously. When the thickness of the high resistance insulating layer is controlled at about 0.35 mm, the electric strength of the resistance reaches the maximum value. Using SF₆ gas in place of air can increase the resistance significantly. In the SF gas environment of 0.2 MPa, under the protection of high resistance insulating layer, the withstand flashover voltage of the resistance reaches 22.5 kV, which is 80 % higher than that without protection.

In order to accelerate the dissipation of the surface charge and improve the flashover voltage of insulator, we propose the plasma fluorination modification technology. Changing the surface modification time, the surface physical, chemical, and dielectric properties of epoxy resin sample with the same formula as insulator was test before and after modification. The results show that as a method of both physical and chemical surface modification, plasma modification can introduce hydrophilic groups to the surface of the sample and change its wettability. With the increase of modification time, the surface roughness of the sample increases at first and then decreases. At the same time, the plasma modification can introduce fluorine to the surface of the material, shallow the surface traps, improve the surface conductivity, and reduce the accumulation of surface charge. Under the selected parameters, the surface flashover voltage increases to the maximum after modification for 9 minutes, and the Weibull distribution calculation shows that the increase rate is about 37.17%. After plasma surface modification for too long, the material structure is damaged, the surface traps become deeper, the surface conductivity and surface flashover voltage decrease.

Polypropylene laminated paper (PPLP) used in DC superconducting cable is in a wrap-around structure. Due to the existence of rectifier, PPLP withstands AC-DC composite voltage, and it is easy to generate partial discharge at the butt gap. Under long-term working voltage, the insulating property of PPLP changes and affects partial discharge. In this paper, the DC electrical ageing experiment was conducted on PPLP in liquid nitrogen, and the butt gap was simulated by internal discharge model. The electric field distribution of internal discharge model was obtained by simulation calculation, and the electrical ageing mechanism and partial discharge results were discussed and analyzed. The results show that with the increase of ageing time, the electrical conductivity and relative permittivity of PPLP show an increasing overall trend; the DC electric strength of PPLP decreases gradually, but still maintained good insulation properties; the intensity of partial discharge increases the partial discharge phase mainly concentrates in the rising stage of composite voltage, and the ratio between AC and DC of composite voltage is the main factor affecting partial discharge.

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.

The core content of 500 kV DC cable joint design is the performance and geometric structure of reinforced insulation material. In this paper, the electric field distribution characteristics of the main insulation and reinforced insulation double-layer dielectric of the DC cable joint were calculated and simulated. The development mechanism of DC cable joint breakdown caused by interface discharge was analyzed. The breakdown characteristics of the dielectric interface between cross-linked polyethylene (XLPE) and silicone rubber (SR) in DC cable joint were analyzed. The results show that the conductivity of the reinforced insulation and the main insulation of the cable joint and the interface tangential electric field strength are the key parameters of the reinforced insulation design. Within the changing allowance of temperature and electric field, the conductivity of the reinforced insulating material should always be less than that of XLPE. The tangential electric field strength of the interface between the main insulation and the reinforced insulation is the key control parameter affecting the operation reliability of the DC cable joint, and its threshold is 2.5 kV/mm under the most unfavorable conditions. The research results provide a new method to solve the design problems of DC cable joints, especially for the reinforced insulation.

The paper proposes a evaluation method for the micro properties of impurity content for cable insulation, which can effectively avoid the effect of subjective factors of manual microscopic observation in the purity evaluation process. On the basis of broadband dielectric impedance spectroscopy method, the change law of dielectric loss factor of 35 kV and 110 kV XLPE cable insulation samples with the test frequency during different thermocycling processes were investigated, and the stress characteristics at the interface between XLPE insulation and impurity during the thermocycling process were simulated. The correlation between the macrophysical parameter broadband dielectric loss and the microscopic property cleanliness for XLPE cable insulation were analyzed. The results show that after 10 cycles of thermocycling between -196℃ and 50℃, the low-frequency dielectric loss factor of 35 kV XLPE cable insulation at 0.1-1.0 Hz is more than doubled, while the dielectric loss factor of 110 kV XLPE sample does not change obviously. The simulation analysis shows that during the thermocycling process, there is interface stress between the polyethylene insulation and the micro-impurities, the stress fatigue enlarges the microscopic defects in the interface area and then accelerates the increase of low-frequency dielectric loss factor.