Composite insulators with a large heating area in a 220 kV operation and maintenance AC line were taken as a sample, the impact of different environmental parameters on the heating and operating performance of the composite insulator was analyzed by conducting power frequency withstand voltage and infrared tests on the heating insulator, as well as physical and chemical property tests on the silicone rubber of the composite insulator. The results show that the abnormal heating of the aged and damp composite insulator sheath is located at the high voltage end. The higher the environmental humidity and the lower the wind speed, the larger the heating range and amplitude. After being dampened, the dielectric constant and dielectric loss of silicone rubber increase significantly, and the heat generation comes from the dielectric loss of the aged sheath on the surface. There are obvious signs of deterioration on the surface silicone rubber of the sheath at the heating point, and the interior of the sheath and the core rod are not affected by the surface heating. The operational performance of the insulator is not affected. In addition, based on the above results, suggestions for on-site maintenance of sheath ageing, moisture, and heat defects were proposed.

Aiming at the problem that the energy storage characteristics of polypropylene (PP) capacitor films reduce greatly under high temperature and high electric field, the polypropylene was modified by melt grafting with maleic anhydride (MAH) at the molecular level, and the effects of grafting monomer content, initiator mass fraction, and reaction temperature on the high-temperature energy storage characteristics of the films were investigated. Then a maleic anhydride grafted polypropylene (PP-g-MAH) biaxially oriented capacitor film with superior high-temperature energy storage characteristics was prepared, and its structure and performances were characterized and tested. The results show that with the increase of monomer content, initiator mass fraction, and reaction temperature, the charge and discharge efficiency of the grafted sample increases at first and then decreases. The graft modification promotes the increase of crystal nuclei and the reduce of spherulite size in PP, which increases the trap depth and trap density of the film effectively, reduces the carrier mobility, and enhances the electric strength and energy storage characteristics at high temperature.

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.

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.

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%.

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.

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).

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%.

In order to investigate the effect of combined heat-force on the performance of ethylene propylene diene monomer self-fusing insulation, ageing experiments with different temperatures and tensile rates were conducted on the ethylene propylene diene monomer self-fusing insulation, and the tensile and dielectric properties of ageing samples were characterized respectively. The results show that during the ageing process, the tensile strength and elongation at break of the sample decrease due to the gradual destruction of molecular structure and swelling of adhesive molecules, and the strong tensile stress will exacerbate the degree of ageing, make the defects gradually develop and expand, and further deteriorate the mechanical properties of the sample. With the increase of ageing time, the polar groups inside the sample increases, the steering polarisation enhances, and the polarisation loss increases. When the stretching rate gradually increases, the increasing rates of relative dielectric constant and dielectric loss factor show the trend of “slow first and fast later”. At the same time, the breakage of molecular chains and the generation of microscopic defects increase the concentration of carrier, and the larger tensile rate weakens the intermolecular forces, reduces the barrier energy level, and makes the carriers easier to migrate, resulting in a continues increase of its volume conductivity. In the later stages of ageing, the molecular chain cleavage under tensile stress is serious, and the thermal expansion of the matrix increases the free volume, leading to a decrease in electric strength. A larger tensile rate will further reduce the trap energy level inside the sample, resgreater decrease in electric strength.

The salt alkali resistance modification of polyurea protective coating of the composite pole can improve the operation reliability of the composite pole in heavily polluted area. In this paper, the surface treatment of montmorillonite was carried out with KH550 coupling agent, and the salt spray protection effect of montmorillonite modified polyurea resin with different contents on pole composite materials was analyzed. The results show that after 28 days of salt spray ageing, the properties stability of montmorillonite modified polyurea resin (sample PFRP-4) with mass fraction of 1.5% is better. The bending and tensile properties were reduced by 12.77% and 25.70%, respectively, and the retention rates of electric strength and flashover electric field strength strength reach 77.60% and 83.83%, respectively. After salt spray ageing, the surface damage degree of PFRP-4 is small, the thermal weight loss is low, and the residual rate is 67.15%. Montmorillonite can effectively fill the free volume and cracks in the polyurea resin, adsorb water molecules and corrosive ions, and reduce the overall water absorption of the coating. The sample PFRP-4 protective coating can effectively improve the hydrophobicity and thermal stability of the composite materials, and has good bonding properties, which can provide a strong guarantee for the operation of the composite pole in the harsh environment such as high salt spray and high humidity.