In order to achieve long-term stable extrusion of insulating materials, a cross-linked polyethylene with different antioxidant content was prepared by melt blending, and the effect of different antioxidant content on the scorch resistance of cross-linked polyethylene was studied. At the same time, the mechanical properties, electric strength, dielectric properties, and thermal properties of cross-linked polyethylene were comprehensively evaluated. The results show that with the increase of antioxidant content, the torque of cross-linked polyethylene decreases gradually, the cross-link time increases slowly, and the scorch resistance of the material is improved. In addition, the temperature of cross-linked polyethylene material is reduced slightly, which ensures the stability of long-term extrusion for material. The conductivity of cross-linked polyethylene does not change significantly with the increase of antioxidant content, while the AC electric strength and dielectric loss increase slightly. The AC electric strength increases by 4.5%, the dielectric loss factor is less than 5.0×10^-4, and the melting and crystallization characteristics do not change significantly.

Using aramid fibrid as reinforcing material and introducing into mica paper-based materials, we manufacture an aramid fibrid/mica composite insulating paper by wet paper with pulp. The morphology, mechanical strength, insulating properties, thermal stability, and glue permeability of the composite paper were systematically studied. The results show that the flake mica and ribbon-like aramid fibrid are orderly stacked to form a “brick-mud” structure. The increase of aramid content makes the composite paper structure more compact, and the mechanical strength also increases. With the increase of aramid content, the gap between mica is filled, and the air permeability of composite paper decreases. The electric strength and thermal stability of the composite paper decrease with the increase of thickness, but the composite paper still maintains good insulating properties and thermal resistance.

In order to study the reliability of nitrile butadiene rubber (NBR) sealing element under the action of extremely low temperature and oil medium, the mechanical properties and microstructure of sealing rings in high-voltage transformers in extremely cold regions were studied. The mechanical characteristics, morphology change, chemical structure characteristics, and thermal response characteristics of the sealing ring after serviced for one year in extremely cold environment were obtained by tensile test, micron indentation test, scanning electron microscope (SEM), infrared spectrum (FTIR), and differential scanning thermal analysis (DSC). The results show that the elastic modulus and hardness of NBR sealing ring decrease in extremely cold environment, which leads to the loss of sealing effect. This is because the surface of sealing ring swell under the joint action of low temperature and oil medium, and micro-cracks appear. Oil immersion in NBR makes the molecular chain spacing increase, and the compliance of main chain of NBR is improved, meanwhile, the molecular structure of NBR changes due to the hydrolysis reaction of cyanide group.

In order to study the performance changes of irradiation crosslinking low-smoke halogen-free flame-retardant insulation layer and sheath layer for photovoltaic cables before and after getting moistened, the insulation layer and sheath layer of photovoltaic cable with various water-immersion time were conducted mechanical properties, thermal extensibility, dynamic thermomechanical analysis (DMA), Fourier transform infrared spectroscopy (FTIR), and volume resistivity tests. The results show that the long-term water-immersion causes hydrolysis of molecular chains in the material, and the entanglement of molecular chains weakens, which lead to decrease of tensile properties of samples. After water-immersion, the initial storage modulus of the insulation layer and sheath layer samples decreases, the adhesion force between filler particles and matrix resin decreases, and the mechanical loss peak of the insulation layer presents double peaks characteristic. With the increase of moistening degree, the EVA in the polyolefin matrix swells, and the free volume increases. Some flame retardant fillers are separate from the binding of matrix and become impurity ions, making the carrier concentration and mobility increase, which leads to continuous decrease of volume resistivity.

From the perspective of inorganic nanoparticles hybrid polyimide (PI), the research status of dielectric constant, conductivity, electric strength, and corona resistance of PI hybrid materials at home and abroad in recent years was reviewed and commented. The influence of different inorganic nanoparticles doping on the electrical properties of PI materials was expounded, the problems existing in the process of PI hybrid were analyzed, and the direction of PI hybrid materials can be further studied was prospected.

The faults caused by internal interface defects of composite insulators is a great threat to the safe and stable operation of power grid. In order to study the influence of different shapes of defects and their sizes and moisture immersion on the electric field distribution of insulators, an isosceles triangle defect model including tip curvature radius parameter was proposed. A 3D model of 500 kV composite insulator was established, and the electric field of defects with different shapes and sizes and moisture ratio were simulated and compared by the COMSOL. The results show that the isosceles triangle defect model can better reflect the tendency of defect developing to the low voltage side. The tip curvature radius of defect has no obvious effect on the air gap, but there is a point effect in the water gap. With the increase of moisture content in the defect, the maximum electric field strength increases gradually. Under the action of point effect and moisture immersion, the electric field strength at the tip of low voltage side is distorted severely, which increases the possibility of partial discharge and accelerates its development to the low voltage side.

Aiming at the contaminant composition of transmission line insulator in Ningxia Yellow River irrigation area are not clear, and the degree of environmental impact is unknown, we subdivided the environment of Ningxia Yellow River irrigation area into 5 categories: industry, agriculture, urban residential area, desert, and grassland, and insulator contaminants samples in the corresponding environments were taken to conduct microscopic morphology, element content, crystal composition, anion and cation composition and content detection and analysis. Meanwhile, the pollution accumulation characteristics of insulators in irrigated and non-irrigated areas were compared and analyzed. The results show that the soil composition in the Yellow River irrigation area determines the basic composition of insulator contaminants. The industrial and agricultural environment have bigger influence on the micro-structure and different ingredients content of the insulator contaminants, and the urban residential area is followed. The pollution accumulation degree of insulators in irrigated areas was obviously higher than that in non-irrigated areas. In order to further improve the operation reliability of the transmission lines in Ningxia Yellow River irrigation area, some suggestions for anti-pollution flashover operation and maintenance are put forward, which can be use as reference for relate operation and maintenance units.

With the development of UHV DC transmission system engineering in China, the voltage level of converter transformers is getting higher and higher, and insulation problems are becoming more and more prominent. The study of partial discharge is of great significance to the insulation condition judgment and equipment life evaluation of converter transformer. In this paper, the insulation characteristics, the process of field tests, and the detection methods of partial discharges and their precautions of converter transformer were introduced, the research achievements of experts and scholars at home and abroad on the partial discharge of converter transformer were reviewed, and the research directions of partial discharge of converter transformer were prospected, which provided a reference for the operation, maintenance, and research of converter transformers.

Biaxially oriented polylactic acid (BOPLA) films were prepared by twin-screw extruder and static stretching machine, and they were buried in outdoor soil. The natural degradation process and mechanism of the BOPLA films were studied by analytical balance, Fourier transform infrared spectoscopy (FI-IR), scanning electron microscope (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The results show that the BOPLA film degrades slowly due to its dense surface at the initial degradation stage. After degrading for 10 months, the dense layer on the surface is eroded seriously, and the degradation goes deep into the film, the degradation is accelerated. The crystallinity, grain size, glass transition temperature, and other properties, which affected by the degradation of crystalline and amorphous regions, reach the peak value after degrading for 3 months, and then show a fluctuating downward trend.

In order to accurately evaluate the maximum impulse voltage which corona resistance enameled wire endured, the corona resistance time of enameled wire under different impulse voltage was tested respectively, and the optimal fitting relationship curve equation between them was analyzed. The results show that the corona resistance time decreases exponentially with the increase of impulse voltage. Because the corona resistance time in the fitting equation has practical physical significance, no matter how the corona resistance time changes, it is greater than zero, which can indirectly solve the maximum impulse voltage that the corona resistance enameled wire can endure.