The cable joint is the weakest link in the cable line, and the contact resistance between the conductor and the connecting pipe at the aluminum alloy conductor cable joint is the key factor affecting the temperature distribution and failure rate of the cable joint. In order to study the influence of different crimping processes on the temperature distribution characteristics of cable joints, a 35 kV aluminum alloy conductor was used as the research object, and the contact resistance between conductor samples with different crimping percentages and connecting tubes were measured through the contact resistance measurement circuit. The quantitative relationshipes between contact resistance and crimping percentage under two crimping processes of pit pressure and confining pressure were obtained. The electro-thermal coupling model of a cable joint with conductor cross-sectional area of 400 mm² was established by COMSOL finite element simulation software, and the corresponding relationship between contact resistance and temperature distribution characteristics of cable joint under different crimping processes was studied. The results show that the contact resistance increases with the increase of the crimping percentage. Under the premise of ensuring that the maximum temperature of the long-term operation of the cable does not exceed 90℃ and meeting the mechanical performance requirements, the crimping percentage under the pit pressing process should be controlled at 27.86%-35.44%, and the crimping percentage under the confining pressure process should be controlled at 16.01%-22.21%. The temperature rise curves of the two crimping processes have the same change trend. The highest temperature of the cable core appears at the position of the connecting pipe, and gradually decreases along the axial direction. The temperature of the outer surface of the joint shows a downward trend as a whole, but the temperature of the connecting pipe increases in a small range due to the existence of contact resistance.

In order to improve the energy storage properties of polyetherimide (PEI) films, the aminated metal-organic framework (ZIF-8-NH₂) was loaded on the surface of graphene oxide (GO) by electrostatic action, and then self-assembled to PEI film surface by intermolecular hydrogen bonding. After annealing, GO was reduced to reduced graphene oxide (rGO), and PEI-rGO@ZIF-8 composite films were obtained, and the effect of the ratios of rGO to ZIF-8-NH₂ on the energy storage performance of PEI composite films were investigated. The results show that the discharge energy density of PEI-rGO@ZIF-8 (1∶15) composite film can reach 8.24 J/cm³ under the electric field of 680 MV/m, and maintain a high charge-discharge efficiency of 88.36%, showing excellent energy storage performance.

The ablation of the buffer layer of high-voltage cables is accompanied by the release of characteristic gas, so the characteristic gas can be used as an indicator for the detection and evaluation of ablation faults. However, the correlation between the type and concentration of released gas and the degree of ablation is still unclear. In this paper, a buffer layer ablation simulation experiment platform was established. After comprehensive consideration, C₂H₆, C₂H₄, C₂H₂, and CO were selected as the characteristic gases for buffer layer ablation evaluation, and the change law of their stoichiometric characteristics with buffer layer ablation degree and moisture content were analyzed. The results show that the average molar mass of characteristic gas decreases with the increase of moisture content in buffer layer, and the ratio of C to H atoms in characteristic gases under humid conditions is higher than that under dry conditions. The concentrations of C and H atoms continuously increase with the burning time, and with the increase of burning time, the concentrations of C and H atoms first decrease, then increase and then decreases, and finally monotonically increase with the increase of moisture degree. Analysis suggests that the differences of damage to the buffer layer structure under different conditions are the reasons for the change in the stoichiometric characteristics of the released gas.

The ternary copolymer of polyvinylidene fluoride, poly (vinylidene fluoride trifluoroethylene chlorofluoro-ethylene) (P(VDF-TrFE-CFE), abbreviated as PVTC) is expected to be used as a new type of capacitor film material due to its high relative dielectric constant. In this paper, the crystal phase structure of PVTC was regulated by optimizing the hot pressing process of thin film preparation, and the influence of different hot pressing temperatures on the crystal phase structure of PVTC thin films was discussed. Then, PVTC composite films doped with low content voltage stabilizer aromatic ketone small molecule 4-acryloxy-2-hydroxyphenylketone (ALRB) were prepared by solution casting method, and the influence law and mechanism of ALRB doping content on the electrical properties of the composite films were studied systematically. The results show that when the hot pressing temperature is 180℃, a multiphase structure coexisting with α phase, β phase, and γ phase is formed inside the PVTC film, which has significant improvement effect on its dielectric properties and energy storage properties. Appropriate amount of voltage stabilizer ALRB can dissipate high-energy electron energy and improve the insulation performance of PVTC films. When the mass fraction of ALRB is 0.5%, the electric strength of PVTC/ALRB composite film reaches 485.7 kV/mm, and the discharge energy density and charge discharge efficiency are 12.12 J/cm³ and 64.4%, respectively.

As a key device in ultra-high voltage and extra-high-voltage transmission projects, the deflagrate accidents of bushings seriously threaten the safe and stable operation of the power system. Adhesive impregnated paper bushing is an alternative to oil-impregnated paper bushings with deflagration risks, while there is relatively little research on the thermodynamic behavior of its core insulating material of epoxy resin impregnated paper during arc faults and the risk of bushing deflagration. In this paper, the thermogravimetric experiments and differential scanning calorimetry analysis at different heating rates were conducted on epoxy resin impregnated paper, and its thermal decomposition process was analyzed. Flynn-Wall-Ozawa (FWO) method and Coast-Redfern (CR) method were used to obtain the pyrolysis kinetic models of epoxy resin impregnated paper at high temperature in an oxygen-free environment. The results show that the thermal decomposition process of epoxy resin impregnated paper in adhesive impregnated paper bushing can be divided into three stages: epoxy melting, endothermic reactions, and decomposition gasification, and the first two stages conform to three-dimensional diffusion model, random nucleation and subsequent growth model, respectively. After an arc breakdown fault occurs in bushing cores, the thermal decomposition mass loss of epoxy resin impregnated paper is as high as 90% under the effect of high temperature. The high temperatures and gas expansion produce high amplitude internal stress inside the core, which leads to core cracking and even explosion.

Cracks will occur inside and on the surface of epoxy resin under the action of complex factors such as strong electric fields and mechanical vibrations, leading to a decline of its insulation performance. Therefore, a water-triggered self-healing microcapsule was prepared by interfacial polymerization, and a water-triggered self-healing microcapsule/epoxy resin composite insulating material was prepared through high-temperature curing. Then the dielectric properties, tensile properties, and electric strength of the composite insulating material were characterized. The results show that the composite insulating material not only maintains good mechanical, insulation, and dielectric properties, but also has excellent self-healing performance, with a self-healing efficiency of 93.45%.

Polypropylene (PP) is the most widely used dielectric material for capacitors, improving its insulation performance is of great significance to improve the energy storage density and reliability of capacitors. In this paper, the action law and mechanism of crystal form on breakdown characteristics of films were studied systematically by adding β-nucleating agent to polypropylene resin, so as to obtain the method of improving the insulation performance which can be popularized in industry. Firstly, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) tests were conducted on the polypropylene resin for its aggregate structure. The results show that the crystallization activation energy of polypropylene resin decreases and the crystallinity increases after adding the β-nucleating agent. Secondly, on the basis of the practical application requirements of capacitor dielectric materials, polypropylene resin was bi-axial oriented to obtain bi-axial oriented polypropylene (BOPP) films. It is found that there are no obvious difference in crystal morphology and surface morphology of the resins with different crystal type after stretching,while the electric strength of the BOPP film containing β-nucleating agent is 7.1% lower than that of the BOPP film without β-nucleating agent. Finally, the BOPP films were subjected to vacuum heat treatment at different temperatures for 1 000 h. The electric strength of the two BOPP films increases with the increase of heat treatment temperature, and the electric strength of the film containing β-nucleating agent increases more significantly, which exceeds that of the resin with α-crystal as the main crystal after heat treatment at 120℃. It is speculated that the reason for this result is that the β-crystal is not conducive to the optimal arrangement of molecular chains during the tensile process, resulting in the migration of electrons more easily and thus reduce the electric strength. However, the vacuum heat treatment near the crystallization temperature can promote the movement of molecular chain segments, optimize the aggregation structure, and ultimately make the electric strength incrase.

High sensitivity defect detection technology is urgently needed to evaluate the health status of gas insulated metal enclosed switchgear (GIS) insulator. In this paper, a defect detection method for GIS basin insulator based on ultrasonic scanning frequency signal injection was proposed. The propagation law of scanning frequency ultrasonic signals on clean/defective basin insulators were investigated by simulation and experiment, and three defects including internal bubbles, surface cracks, and surface metal particle attachment were considered. In the simulation and experiment, the ultrasonic emission and reception probes were located opposite the flange of the basin insulator. The ultrasonic scanning signal was a frequency conversion sine wave with an amplitude of 1 V and a frequency range of 0.5-1 MHz, which was energized by the transmitting probe and injected into the basin insulator through a flange, and the ultrasonic signal was received by the receiving probe on the opposite side. The results show that the ultrasonic signal directly propagates through the basin insulator to the receiving piezoelectric probe, and the amplitude of the time-domain ultrasonic signal received on the defective insulator is higher than that on the clean insulator, but it is still difficult to be used as a basis for evaluating the health status of the insulator. The main frequency of ultrasonic signals propagated through detective insulators is lower than that propagated through clean insulators. The main frequency signals propagated through clean, crack containing, metal particle defective, and bubble defective insulators are 24.00, 14.83, 10.51, and 12.13 kHz, respectively, which can be used as the basis for defect detection of GIS basin insulators.

Polypropylene (PP) insulation is an important development direction of environmentally friendly recyclable cable insulation materials. However, isotactic PP insulation suffers from issues such as high low-temperature modulus, poor toughness, and low elongation at break. Although the introduction of elastomers into PP insulation through blending or copolymerization methods can optimize its mechanical properties, it also leads to a severe decline in insulation performance. For this purpose, this paper reviewed the research progress on strengthening the performance of cable insulation based on chemical grafting modification. At first, we comparatively analyzed the influence patterns and mechanisms of three types of grafting monomers—polar small molecules, high-energy electron/photon-trapping small molecules, and free radical scavenging small molecules—on the dielectric properties of cable insulation, including space charge accumulation, breakdown, and electrical tree degradation, and proposed the optimal method for chemical grafting monomers. Then different grafting modification methods such as solution grafting, melt grafting, solid-phase grafting, suspension grafting, and radiation grafting were compared and analyzed. At last, the problems in the current chemical grafting modification methods for PP cable insulation were summarized, and the development and application of chemical grafting modified PP cable insulation materials were prospected.

To solve the current problem that the monitoring methods of power cable are relatively simple and lack of multi-parameter comprehensive monitoring and judgment, this paper integrated various partial discharge signals of cable joints, and proposed a cable joint fault monitoring method based on deep learning fusion evidence theory. Then fault identification research was conducted for three situations, including no defects, internal insulation defects, and joint moisture in cable joints. According to convolutional neural network algorithm model, the partial discharge signal graphs were trained and tested separately, and data fusion was carried out by D-S evidence theory to realize fault type identification. The results show that for the situation of internal insulation defects and joint moisture, the best recognition effect of single information source is high frequency partial discharge, and its average recognition rate can reach 85.6%, and the average recognition rate of ultrasonic method is the lowest, which is 78.7%, while the average recognition rate of the identify method proposed by this paper can reach 95.7%. When there is a misjudgment in the recognition result of one of the multi-dimensional information sources, D-S evidence theory fusion can eliminate the interference of the wrong information source, accurately identify the discharge type.