In order to explore the reasons for the differences in the properties of polyethylene cable materials at home and abroad, the molecular weight distribution, long branch chain content and short branch chain content of the materials were measured by gel permeation chromatography (GPC), rotational rheological test, and self-nucleation annealing thermal classification (SSA), and the relationship between the molecular chain structure of one domestic and two imported 500 kV cross-linked polyethylene cable materials and their dielectric properties were discussed. The results show that the order of long-chain chain content in polyethylene from small to large is: domestic sample, imported B sample, imported A sample. The order of short chain content from small to large is: imported sample B, imported sample A, domestic sample. Among them, the imported sample A has higher content of long-chain chains, which is conducive to the formation of ordered molecular arrangement and crystallization, and further improve its withstand voltage level. Excessive short chain content in domestic samples can hinder the molecular crystallization, resulting in lower breakdown strength. In addition, the differences in the molecular chain structure of the three types of polyethylene have little effect on their dielectric constant, dielectric loss factor, and resistivity.

The ultra-high frequency (UHF) method for detecting partial discharge (PD) is currently one of the important means to evaluate the state and insulation performance of gas insulated switchgear (GIS). In this paper, in order to solve the problem of a large number of missing and false alarms in UHF detection of GIS partial discharge, GIS insulator with metal foreign object attached on the surface was conducted long-term constant voltage experiments. The successful capture probability of discharge signal was analyzed by combining with the existing UHF detection strategies, and optimization schemes of the existing UHF signal detection strategies were proposed from detection time and detection threshold. The results show that the partial discharge of metal foreign object defect attached on the insulator surface has intermittent characteristics, and the existing UHF live detection and online monitoring strategies have low detection probability of discharge. The capture probability of effective discharge can reach 85% by extengding the detection time to 2 247 seconds in optimization of live detection strategy. The detection probability of PD Event can increase by extengding the measurement time of forming a partial discharge event (PD Event) and reducing detection threshold in optimization of online monitoring strategy. In engineering application, the combination of appropriate measurement time and detection threshold can be selected to detect the intermittent discharge.

In order to solve the problem of printing contamination on the surface of silicone rubber cables, the application of low temperature plasma jet in surface treatment of silicone rubber was proposed in this paper. Ar plasma jet was generated with needle-ring structure electrode driven by AC power source, and the surface of silicone rubber cables was dynamically treated at different moving speeds. The influence of processing speed on the hydrophobicity, surface voltage, and breakdown strength of silicone rubber cable was systematically studied. The changes in surface physical morphology and chemical composition of silicone rubber were detected by SEM and EDS. The results show that static jet treatment can cause an increase of the material surface temperature, while dynamic treatment can significantly reduce the temperature rise. The water contact angle and flashover voltage of silicone rubber slightly decrease after treatment. With the increase of processing speeds, the hydrophobic and electrical insulation performance gradually recover. Under the speed of 5 mm/s, the anti-ink adhesion of silicone rubber surface is significantly improved. It can be concluded that the degree of cross-linking polymerization on the surface of silicone rubber increases after the plasma jet treatment, and the diffusion movement of interface molecules at the interface is hindered, which decrease the anti-ink adhesion of the silicone rubber surface.

In order to improve the accuracy of live detection of line porcelain insulator degradation, the influences of layout methods and deterioration degree on the voltage distribution characteristics of high-voltage AC insulator strings were studied in this paper. Firstly, a finite element simulation calculation model with single voltage distribution of AC 220 kV porcelain insulator strings under different layout methods was established, and the voltage distribution characteristics of the insulator strings were simulated and analyzed. Then, combined with the actual measured voltage distribution of 220 kV AC transmission line insulator string in Shandong province, the consistency between simulation calculation and actual measurement was verified. The results show that the tower type of transmission circuit, the number and layout method of the insulator string, and the position and deterioration degree of the degraded insulator have great effects on the voltage distribution characteristics and deterioration discrimination of the insulator strings. Among them, the maximum distributed voltage difference of different tower types can reach 35%, and the maximum distributed voltage difference of different layout methods can reach 18%. The deterioration situation of insulators at different positions can be judged by the distribution voltage drop ratio.

Metallized polypropylene film capacitor has the characteristics of high reliability, self-healing, and low dielectric loss. However, it needs to withstand the combined action of strong direct current electric field and high temperature thermal field for a long time during the working process, which makes the space charge easy to accumulate inside the polypropylene dielectric film, resulting in the degradation of its electrical insulating properties. A self-healing model of metallized polypropylene film was established in this paper. The changes of self-healing area at the self-healing point under different self-healing development time and applied voltage were studied through the evaporation model of metal layer, and the changes of space charge density in the discharge channel under different self-healing development time, applied voltage, and temperature were studied by using the bipolar carrier transport model, so as to explore the microscopic mechanism of self-healing of metallized polypropylene film. The results show that there is a linear relationship between the evaporation area of metallized film and the self-healing development time. With the increase of the applied DC voltage and temperature, the charge migration process in discharge channel strengthens, and the electrons and holes in discharge channel are more likely to migrate and recombine with the charges of opposite polarity. With the self-healing process progresses, the charge amount injected into the discharge channel increases gradually, and the migration of charge to both ends of the discharge channel intensifies, resulting in uneven potential distribution in discharge channel and the electric field will distort in discharge channel.

In this paper, the space charge formation mechanism and space charge effect were systematically described. Three methods of constructing trap energy levels, including filling inorganic nanoparticles, doping small molecule semiconductors, and molecular structure design, were emphatically reviewed. The design strategy to improve the energy storage performance of the dielectric material were deeply discussed, and the preparation methods of high performance polymer dielectric materials were prospected.

In this paper, combined with the application of insulation varnishes on the market in traction motors, the research status and development trend of insulation varnishes for traction motors at home and abroad were reviewed. The insulation varnish systems developed from 180-class (H) diphenyl ether system to the 200-class (N) epoxy anhydride system, and then to the 220-class (R) silicone insulation system, indicating that the insulation varnish system for traction motors were developing towards high heat resistance direction, and the future development and application trend was still high heat resistant insulation varnish systems.

The insulation resistance of the outer sheath of high-voltage cables is an important parameter for measuring the insulation state of high-voltage cables. In this paper, an online monitoring method based on metal sheath circulation current was proposed to evaluate the insulation resistance of the outer sheath of high-voltage cables, so as to realize the real-time monitoring of the insulation state of high-voltage cables. The formation of mental sheath circulation current and its relationship with the insulation resistance of outer sheath were analyzed, and a calculation model was derived. Then the online monitoring of high-voltage cable with single-end grounding and cross-linked grounding have been carried out. The results show that the error between the online monitoring method and the offline measurement method is less than 20%, and the measurement effect of the method is significantly better in the cross-linked grounding segments than in the two-sided cable segments, which is of great significance for the condition monitoring and fault location of the metal sheath of high-voltage cables.

In order to investigate the impact of thermal ageing on the development of DC partial discharge of surface scratched cross-linked polyethylene (XLPE) cables, a surface scratched defect model weas made using a physical 10 kV cable, and subjected to the accelerated thermal ageing treatments with different times. The partial discharge characteristics of defective cables under DC voltage were studied using the pulse current method. On basis of the variation of partial discharge with voltage applying time, the statistical charts of the maximum discharge capacity, average discharges capcity, and discharge repetition rate in different discharge intervals were extracted. Then based on the charge transport theory, partial discharge and charge transport models were proposed to explain the partial discharge results of defective cable. The results show that the initial partial discharge voltage of the defective cable increases with the increase of thermal ageing time, the discharge quantity-time spectrum shows "comb" discharge characteristics. As the thermal ageing time increases, the average discharge capacity and discharge repetition rate of the defective cable in the interval greater than 100 pC decrease gradually, and the “comb" discharge characteristics disappear completely after 21 days of ageing, demonstrating the self-healing ability of partial discharge. During thermal ageing, the surface oxidation of XLPE scratched defects produces charge traps, resulting in a uniform and dense space charge layer, which reduces the internal electric field of the defects and weakens partial discharge in defective cables. The research results provide data support for the study of DC partial discharge of XLPE cable defects.

The molecular chain structure has great influence on the electrical insulation properties of silicone rubber. In this paper, the regularity and mechanism of the blending of different ratios and types of blended silicone rubber on the electrical properties of composite silicone rubber were explored through a combination of experiments and molecular simulations. The results show that the electric strength of phenyl silicone rubber/vinyl blended silicone rubber (PMVQ/MVQ) improves significantly, when the mass fraction of PMVQ is 15%, the volume resistivity of PMVQ/MVQ composite is 1.04×10¹⁶ Ω·cm, and the electric strength is 106.87 kV/mm, which increase by 1.77 times and 13.22% than that of the vinyl silicone rubber. The dielectric properties of trifluoropropyl silicone rubber/vinyl blended silicone rubber (FMVQ/MVQ) improves, when the mass fraction of trifluoropropyl silicone rubber is 15%, the dielectric constant of FMVQ/MVQ composite is 3.74, which is 40.07% higher than that of vinyl silicone rubber. Molecular simulation results show that the free volume of PMVQ/MVQ decreases with the increase of phenyl silicone rubber content, and the free volume of FMVQ/MVQ increases with the increase of trifluoropropyl silicone rubber content, which is consistent with the breakdown phenomenon of composite silicone rubber.