In order to solve the problem of interface breakdown and surface discharge caused by uneven distribution of electric field of power cable and its terminal insulation, the structural parameters of 35 kV cold shrinkable power cable terminal were optimized to improve its insulation level in this paper. Firstly, the influence of axial length and end radius of stress cone on the terminal electric field distribution was analyzed based on COMSOL simulation software, and the optimal combination of terminal structural parameters was obtained. Then the power cable terminal samples were prepared, and the performance indexes were verified by power frequency AC voltage resistance and partial discharge tests. The results show that the axial length of the power cable terminal stress cone is the main factor affecting the change and distribution of interfacial electric field, and the change of terminal radius has little effect on the terminal electric field. The increase of axial length of stress cone alleviates the interfacial electric field intensity, but it is easy to cause discharge along the surface. The optimal axial length and upper radius of stress cone are 25 mm and 2.5 mm, respectively.

The study on the gas production law of stator bar for hydrogenerator under high temperature and partial discharge can provide a basis for insulation ageing monitoring of hydrogenerator on the basis of decomposition gas method. Aiming at the stator bar used in hydropower station, a high temperature pyrolysis experimental platform was built to study the pyrolysis gas of stator bar at 100, 120, 150 and 250℃. A partial discharge experimental platform of stator bar was established to study the ozone generation law of stator bar under partial discharge. The results show that CO and CO₂ are suitable used as the early characteristic gases of stator bar with high temperature fault. When there is partial discharge on the stator bar surface, the ozone concentration is related to discharge voltage and time. Under the same discharge condition, the ozone concentration rate generated by semi-conductive silica gel is higher and it has stronger corona resistance. Filling stator slot with semi-conductive silica gel is beneficial to the safe operation and on-line monitoring of stator bar.

C₆F₁₂O is a potential substitute gas for SF₆. To explore the decomposition characteristics of C₆F₁₂O/CO₂ mixed gas under floating electrode defect and different partial discharge intensity, a partial discharge decomposition test platform was built, and 96 h partial discharge decomposition experiments were conducted on C₆F₁₂O/CO₂ mixed gas under different applied voltages. The decomposition components were quantitatively analyzed by gas chromatography. The relationship between the decomposition components content, gas production rate, characteristic gas ratio and partial discharge intensity was studied respectively. The results show that the change rule of concentration, gas production rate of four typical products (CF₄, C₂F₆, C₃F₈, C₃F₇H) are different, which can be used as the characteristic component to judge the partial discharge intensity. The concentration relationship of characteristic components is c(CF₄)>c(C₂F₆)≈c(C₃F₈)>c(C₃F₇H), and the gas production rate relationship is similar. The concentration of characteristic components shows a “linear-saturated” growth with the increase of discharge intensity. It is preliminarily suggested that using c(CF₄)/c(C₃F₇H) as the auxiliary basis, and c(CF₄+C₂F₆+C₃F₈)²/c(C₃F₇H)² as the main basis, the PD intensity and defect severity can be judged combined with component content and gas production rate, which provide reference for finding out the operation and maintenance monitoring methods applicable to C₆F₁₂O/CO₂ mixed gas insulation equipment.

The silicone rubber composite insulators operating in humid and hot areas has the problem of microbial contamination caused by mold adhesion, and the effect of mold as a special biological pollution on the performance of silicone rubber insulators is still unclear. In this paper, the suspended insulator strings were contaminated by mold, and their surface flashover characteristics were analyzed under different pollution levels. The influence of mold contamination on the surface flashover properties of insulator was studied by hydrophobicity analysis, scanning electron microscopy, and infrared spectroscopy. The results show that for the insulators with the same pollution level, when there is mold pollution, the mold would damage the surface structure of silicone rubber compared with insulators without mold pollution, resulting in a significant decrease in the hydrophobicity of silicone rubber, and thus the flashover voltage is reduced significantly. Compared with the control group, the surface flashover voltage can be reduced to 76% of the original level at the lowest. However, under the same pollution level, when the mold concentration reaches 107 pcs/cm², there is an inflection point for the decrease of surface flashover voltage, and the decline rate slows down and tends to saturation. In summary, the synergistic effect of mold adhesion behavior and natural ageing of silicone rubber makes the mold mycelium form micro holes on the surface of insulator, resulting in the breakage of silicone rubber molecular chain, reducing the flashover voltage of insulator, and affecting the stable operation of silicone rubber insulators.

In order to develop an on-line monitoring technology for cable insulation status, we analyzed the harmonic components of resistive current by simulating the metal spike in XLPE cable insulation, which provided theoretical and experimental support for cable insulation diagnosis based on the harmonic components of resistive current. Firstly, the conductivity characteristics of XLPE were simulated and theoretically analyzed based on the jump conductivity model of polymer. Then, a simulation model of metal spike defect in XLPE was established, and the harmonic components of resistive current density under different needle curvature radius and needle plate spacing were simulated and analyzed. Finally, three kinds of XLPE metal spike defect samples with different specifications were made, and confirmatory experiments were conducted under the conditions of 30 μm of needle tip curvature radius and 2 mm of needle plate spacing, 90 μm of needle tip curvature radius and 3 mm of needle plate spacing, and 30 μm of needle tip curvature radius and 3 mm of needle plate spacing. The results show that there is metal spike defect in XLPE insulation, due to the sharp increase of local electric field strength, the conductivity characteristics of the insulation material will repeat between the Ohmic and non Ohmic regions with the change of AC voltage waveform, resulting in the distortion of resistive current waveform and the addition of higher-order harmonic components. When there is metal spike defect in XLPE insulation, there are obvious 3rd and 5th harmonic components in the resistive current, which constitutes the main components of resistive current harmonic component. As the severity of metal spike defect increases, the harmonic distortion rate of resistive current and conductivity distortion rate increase significantly, and the harmonic distortion rate can be used as a characteristic quantity to judge the severity of defect.

In the process of transportation and laying, the submarine cable will inevitably be twisted. If the twisting angle is too large, it will cause irreparable damage for the submarine cable. In this paper, a torsion model of submarine cable was established by finite element method, and the characteristic parameters that can effectively reflect the mechanical characteristics of submarine cable were determined by analyzing the temporal and spatial distribution characteristics of stress and strain. The threshold values of each characteristic parameter when torsion failure occured were established, and the mechanical parameter system that can represent the torsion behavior of submarine cable was established. The results show that the axial stress distribution of the submarine cable is more uniform at the initial stage of torsion. With the increase of torsion angle, the axial stress distribution of cable body will fluctuate. A parametric system including copper conductor stress, XLPE insulating layer stress, lead alloy stress, armor layer stress, and torsion angle can be established for parametric evaluation of submarine cable torsion behavior.

Kelvin probe force microscope (KPFM) is an important tool to measure the surface potential of materials with nanometer resolution. Because of its sensitivity to the surface charge of materials, it has been widely used in the research of dielectric charge behavior in recent years. This paper introduced the principle of KPFM, summarized the latest research progress of KPFM applied to charge behavior in dielectrics, focused on the analysis of the diffusion and migration mechanism of surface and interface charges in dielectrics. And the application of KPFM in typical dielectrics such as inorganic materials, nanocomposites, and ferroelectric materials were also reviewed.

Defects will occur during production and operation of insulator, which will cause the accumulation of surface charge, and affect the distribution of electric field of insulators. In serious cases, surface flashover will occur, and then affect the operation safety of electrical equipment. Therefore, it is of great significance to study the nondestructive testing and evaluation methods of defects in insulators. Firstly, this paper summarized the influence of insulator defect types such as bubble, crack, and metallic foreign matter on insulator insulation performance, and analyzed the generation and development mechanism of different defects. Then, the testing principle and research status of new nondestructive testing methods based on acoustic, optical, and thermal characteristics were summarized and introduced. Finally, the detection methods were comprehensively evaluated from the perspectives of speed and accuracy, the detection effects of different detection methods on insulator defects were evaluated, and the research direction of insulator defect detection in the future were prospected.

In order to improve the ageing resistance of insulating paper in oil-immersed transformer, three kinds of common silane coupling agents were selected to modify the insulating papers by immersing. The obtained samples were subjected to the combined thermal ageing test of oil paper at 130℃ for 35 days, and the tensile strength, permittivity, and breakdown voltage of the insulating papers were measured periodically. The results show that all the three kinds of silane coupling agents can improve the ageing resistance of insulating paper, the insulating paper modified by 3-aminopropyltriethoxysilane almost maintains the original three-dimensional network structure of cellulose during the thermal ageing process, and it exhibits the optimal mechanical strength, dielectric properties, and breakdown resistance.

In order to obtain epoxy adhesive materials with high thermal stability for metal foil resistors, combining with molecular simulation and experiment, we studied the effects of molecular structures of methyl hexahydrophthalic anhydride (MeHHPA), methyl tetrahydrophthalic anhydride (MeTHPA), and hexahydrophthalic anhydride (HHPA) on the thermodynamic properties of epoxy adhesive materials for metal foil resistors. Firstly, the cross-linking models of three kinds of acid anhydride molecules and fluoren-based epoxy resin (DGEBF) were established, respectively, and the macroscopic thermodynamic parameters of the cross-linking models were analyzed through molecular simulation calculation. Secondly, the influence mechanism of the molecular structure of acid anhydride on the thermodynamic properties of the cross-linking system was explained according to microscopic parameters. Finally, the simulation results were verified by experiments. The results show that hexahydrophthalic anhydride system has the smallest free volume (FFV) and mean square displacement (MSD), and the free volume proportion is only 15.15%. In the experiment, the change trend of thermodynamic properties of the three kinds of curing anhydride system is consistent with the simulation results. The hexahydrophthalic anhydride system has the best thermodynamic performance, and its glass transition temperature reaches 435 K, bending strength reaches 84.46 MPa, and volumetric thermal expansion coefficient is only 1.65×10^-4 K^-1.