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.

Interfacial discharge between XLPE and SIR in cable joints is one of the main causes of cable failure. In order to improve this phenomenon, the XLPE sample surface was treated by plasma silicon deposition with different time, and the micro-morphology and interface discharge tests were carried out. The results show that the plasma silicon deposition technology can effectively improve the voltage resistance of XLPE/SIR interface. With the increase of plasma silicon deposition treatment time, the surface roughness of XLPE sample decreases at first and then increases, and its change trend is the same as that of the initial discharge voltage, breakdown voltage, and voltage increase amplitude of XLPE/SIR interface, and is opposite to that of the surface resistivity. The XLPE sample after 3 min of plasma silicon deposition has the smallest surface roughness (R _a=41.8nm) and the largest surface resistivity (857×10¹² Ω). Under this treatment time, the XLPE/SIR interface has the largest actual contact area, the fewest micro-pores, and the largest increase in breakdown voltage. Among them, the breakdown voltage increases by 66.7% compared with the untreated XLPE/SIR interface.

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.

High temperature liquid nuclear magnetic resonance (¹³CNMR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were used to study three kinds of polypropylene resins for DC capacitors at home and abroad with different temperature resistance grades, and analyze the effect of microstructure on electrical properties. The results show that the isotactic index, intermolecular chain defect distribution, and molecular weight characteristics jointly affect the crystallization characteristics of polypropylene, and thus affect the final high temperature dielectric properties of materials. The isotactic index of 5 units of imported polypropylene resin is greater than 97%, and the intermolecular chain stereodefect distribution is narrow (I=1.075), the weight average molecular weight is higher and the molecular weight distribution index is larger (PDI>5.6), showing excellent high temperature insulation properties (the electric strength α=533 kV/mm). While the molecular weight distribution of domestic polypropylene resin is narrow (PDI<5), the weight average molecular weight is lower, the isotactic index of 5 units is less than 97%, and the intermolecular chain stereodefect distribution is wider (I=1.106), which leads to its poor high temperature insulation performance and low electric strength (α=497 kV/mm).

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.

Surface flashover at the gas-solid interface of basin type insulator is the key problem that causes the ultra high voltage GIS/GIL failure, and it is the technical bottlenecks restricting the development of advanced electrical transmission system. In order to improve the DC flashover performance of the basin type insulator in SF₆/N₂ gas mixture, the zinc oxide (ZnO) nanoparticles with different contents were added to the epoxy resin to obtain epoxy/zinc oxide (EP/ZnO) coatings, and the EP/ZnO coatings were coated on the surface of epoxy material. Then the transport parameters and flashover performance were tested. The results show that EP/ZnO coating increase the shallow trap density and reduce the shallow trap energy level of epoxy composite, and increase the carrier mobility. The electrical conductivity of the epoxy materials coated by EP/ZnO coatings with 15% and 20% ZnO mass fraction show nonlinear characteristics, the existence of the coatings can reduce the electric field distortion and promote the dissipation of surface charge. The EP/ZnO coating can remarkably uniform electric field distribution and effectively inhibit the charge accumulation on the surface of epoxy materials, and improve the DC flashover performance. When the mass fraction of ZnO is 20%, the DC flashover voltage of the epoxy composite increases by 15.42%.

Polymer-based nanocomposites have received much attention for their application prospects in the development of capacitors with high energy storage density. In this paper, ultra-thin barium niobate (Ba₅Nb₄O₁₅, BNO) nanosheets were prepared by hydrothermal method, and were used as fillers to prepare nanocomposite films by combing with polyvinylidene fluoride trifluorochloroethylene (PVDF-CTFE) and polymethyl methacrylate (PMMA). The effects of ultra-thin BNO nanosheets on the delectric properties and energy storage properties of polymer composite films were studied. The results show that the dielectric constant and electric strength of polymer nanocomposite films increase significantly with a low BNO addition content, and thus the energy density increases. When the mass fraction of BNO is 0.5%, the maximum energy density of the nanocomposite film reaches 13.96 J/cm³, which is 2.6 times higher than that of pure P(VDF-CTFE)/PMMA polymer, and the energy storage efficiency reaches 67.4%.

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%.

To improve the accuracy of cable insulation status assessment, this paper proposed an assesement model of insulation condition based on Bayesian optimization (BO) algorithm and light gradient boosting machine (LightGBM) algorithm. First, all the features in the dataset were combined to form different feature subsets. By traversing all the feature subsets, the optimal feature combination corresponding to the highest accuracy from five-fold cross-validation was identified to complete the input feature selection. Then, the BO algorithm was used to optimize seven hyperparameters in LightGBM. Finally, the proposed BO-LightGBM algorithm was used to assess the cable insulation status. The results show that the feature subset method proposed in this paper can better improve model performance compared with principal component analysis (PCA) and mutual information-based feature selection methods. After optimization by the BO algorithm, the accuracy of the LightGBM model is further enhanced. Compared with particle swarm optimization (PSO) algorithm and genetic optimization (GA) algorithm, the computational efficiency of BO algorithm increases by approximately 80% and 86.9% at the same accuracy level, respectively. Furthermore, compared with other commonly used machine learning algorithms, the performance metrics of the proposed model are optimal.

To improve the thermal ageing resistance of crosslinked polyethylene (XLPE), different contents of anti-ager 2-mercaptothiazole (MB) were blended with PE, and then MB/XLPE sheet samples were prepared through electron irradiation process. The effect of MB content on the crosslinking degree, thermal elongation performance, insulation properties, oxidation induction period, and carbonyl index of XLPE were studied. The results show that with the increase of MB content, the gel content and thermal elongation performance of MB/XLPE composites reduce, while the volume resistivity maintains stable. The addition of MB significantly extends the oxidation induction period and suppresses the carbonyl index growth of XLPE during thermal ageing. When the weight part of MB is 1, the oxidation induction period of MB/XLPE significantly increases from 0.9 min (for pure XLPE) to 80 min; after thermal ageing for 168 h at 165℃, and the carbonyl index of MB/XLPE only increases from 0.04 to 0.06, indicating marked improvement in thermal ageing resistance. Based on the Arrhenius equation, it is concluded that this MB/XLPE exhibits a service life of 76.2 years at 90℃ which is 2.5 times longer than that of conventional XLPE.