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.

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.

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.

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%.

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.

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%.

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.

To investigate the ageing characteristics and lifetime evaluation methods of graft-modified polypropylene cable insulation materials, accelerated thermal ageing tests were conducted on the samples at different temperature, and the changes in electrical and physicochemical properties of graft-modified polypropylene cables at various ageing stages were studied. The variation of key characteristic parameters, such as melting temperature, relative dielectric constant, and elongation at break with ageing time was analyzed. The results show that the melting temperature, electric strength, and elongation at break are significantly correlated with ageing time, and these parameters can be used as effective indicators for assessing the ageing degree of graft-modified polypropylene cable insulation materials.

To investigate the influence of water on the breakdown position of oil-filled cable terminal, this study simulated and analyzed the failure reason caused by water in the 220 kV oil-filled cable terminal. A cable test platform was established in the laboratory, and the influence of the grounding state and electric field strength on the breakdown position was simulated. The partial discharge (PD) quantity and water film height of the cable in different grounding states and at different electric field strength were recorded by using high frequency current partial discharge detector and camera. The results show that the water content in oil, grounding state, and electric field strength are the important factors affecting the fault location of oil filled cable terminal. When the water is immersed in the cable terminal and reaches a certain amount, and the cable terminal is directly grounded, the higher the electric field strength, the more water molecules escape from the oil-water interface, the higher the water film height, the longer the distance between the breakdown point and the upper surface of stress cone, and the larger the partial discharge. The intensity of PD is positively correlated with water film height, and the silicone oil degradation defects within the cable terminal can be evaluated by partial discharge, which provides a reference for evaluating the insulation status of oil-filled cable terminal.