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 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.

Ceramizable silicone rubber composites were prepared by using kilchoanite as ceramic filler, glass frit as flux, and nano silica as reinforcing agent. The effect of the content and size of kilchoanite on the tensile properties of the composites was studied. The ceramic specimens were obtained by sintering the composites at 1 000℃, and then the microstructure of its fracture surface was observed. The phase change of ceramic specimens was analyzed by X-ray diffraction, and its linear contraction and flexural strength were measured. The results show that the increase of the kilchoanite with the same particle size can reduce the tensile strength of the composites, while increase the elongation at break. Under the same content, the kilchoanite with a smaller size can improve the tensile strength of the composites. When the content of kilchoanite is too high or too low, the flexural strength and density of the ceramic specimens decrease. With the decrease of the size of kilchoanite, the flexural strength of the ceramic specimens increases, while the linear contraction also increases. The maximum flexural strength of the ceramic specimens can reach to 58.57 MPa by changing the content and size of kilchoanite.

In order to guide the application of composite cross arms in heavy ice areas, we investigated the icing characteristics of glass fiber reinforced composite material and composite insulated crossarms in this paper. The results show that the icing amount and ice flashover voltage of blank sample under vertical suspension are better than that of horizontal suspension, and its icing amount is less than that of pure aluminum rod and Q345 steel rod with the corresponding hydrophilic. The icing amount of the composite material coated with PRTV coating is less than that of the blank sample, its flashover voltage increases sharply; the ice surface adhesion value is the least, which is 19% of ice surface adhesion value of pure aluminum rod, while the ice surface adhesion value of the blank sample is 78% of pure aluminum rod. The ice coating characteristics of the silicone rubber composite insulated crossarm are just the opposite of that of the composite material sample. Compared with vertical suspending the same composite insulator, when the insulators are horizontal suspending, the icing amount of composite insulated crossarm suspension reduces by 30%, and the flashover voltage increases by 51%.

High-frequency copper-clad laminate is the core foundation to the development of 5G related industries, it has high technical threshold and broad market prospects. In order to clarify the development trend of high-frequency copper-clad laminate field, we comprehensively excavated and deeply studied the patent big data of high-frequency copper-clad laminate and its key technologies, including resin, fiber cloth, filler, and copper foil. The results show that the field of high-frequency copper-clad laminate is still in a period of rapid development, and the technology evolution of resin, fiber cloth, filler, and copper foil are aimed at achieving stable dielectric constant and low dielectric loss. Companies from the USA and Japan occupy the dominant position, the application amount of patent form Hitachi, Sumitomo, Panasonic, Mitsubishi and other Japanese companies are in the front rank. The research on high frequency copper-clad laminate in China starts late but develops rapidly, with two major research and development highlands formed in Guangdong and Jiangsu, and advantageous enterprises emerged such as Shengyi Technology and WAZAM New Materials. However, on the whole, patent technologies of China lack core competitiveness and face strong patent barriers. Accordingly, the countermeasures and suggestions for the high-quality development of high-frequency copper-clad laminate industry in China are put forward.

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.

Compared with other dielectric materials, polymer-based all-organic composite dielectric materials have the advantages of high electrical strength, low dielectric loss, light weight, and excellent mechanical processing performance, and is more suitable for practical applications. In this article, the research progress of polymer-based all-organic composite dielectric materials with the matrix of pure polyvinylidene fluoride (PVDF), PVDF copolymers, and other polymers is reviewed. Some problems still faced in capacitor energy storage and practical application are discussed, and its future development is prospected.

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.

During the operation process, property deterioration of ethylene propylene diene monomer (EPDM) cable is often caused by multiple stresses. In order to explain the variation law and mechanism of dielectric properties of EPDM cable under the extrusion stress and thermal stress, we took EPDM for cable insulation of coal cutter as an object to study. The dielectric spectroscope of EPDM under the combined action of extrusion pressure and thermal stress was measured. The characteristic parameters of dielectric spectroscopy were obtained by simulating the dielectric spectroscopy according to the expression of complex permittivity from the single relaxation Cole-Cole model modified by DC conductivity. The change rule of the DC conductance and relaxation time constant was analyzed. The results show that temperature and extrusion pressure have obvious effects on the complex dielectric constant of EPDM. At a higher temperature, the increase of the real part of the complex permittivity at the lower frequency is obvious. Under the effect of DC conductivity and polarization, with the increase of extrusion pressure and temperature, the increase trend of real part of the complex permittivity at low frequencies slows down, while the real part decreases gradually at higher frequencies. Therefore, the change of DC conductance caused by extrusion stress and temperature is the key to the change of the complex dielectric constant of EPDM.