Reasonable prediction of the ageing state of cross-linked polyethylene (XLPE) cables and timely replacement of severely aged cables are very important for the stable operation of power grid. In this paper, XLPE insulated cable samples were subjected to accelerated thermal ageing test at 145℃.The microphysical and chemical properties of these samples were analyzed, and the correlation between dielectric parameters and microstructure of terahertz frequency range was established. The results show that with the increase of aging time, the crystallinity and thermal stability of XLPE decrease, while the carbonyl index increases, indicating that the ageing degree of XLPE is gradually intensified. In the terahertz frequency range, the real part of the dielectric constant is affected by the combination of multiple structural factors such as crystallinity and polar group content, resulting in an unclear relationship with ageing time. However, the change of the imaginary part of dielectric constant is mainly caused by the dipole high elastic polarization of polar groups, showing a trend of gradually increasing with the ageing time. After fitting, it is found that the imaginary part of dielectric constant is positively correlated with the carbonyl index. Therefore, the imaginary part of dielectric constant in the terahertz frequency range can well reflect the ageing degree of XLPE.

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.

In this research, cyanate ester-bismaleimide-hydrocarbon (BT-CH) composite resin system and BT-CH copper clad laminates (CCL) were prepared by introducing hydrocarbon (CH) resin into ester-bismaleimide (BT) resin system. The curing kinetic parameters of BT-CH composite resin system were studied by differential scanning calorimetry (DSC), Fourier infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The dielectric loss (D_f) and thermal oxygen ageing properties of BT-CH composite resin were investigated after curing. The results show that the reaction order, activation energy, and frequency factors of BT-CH composite resin system are smaller than those of BT system, CH can promote the curing reaction of BT. According to the FTIR spectra of BT-CH CCL, the characteristic peaks of cyanate group, imide group, and vinyl group disappear or weaken, while that of triazine ring appear, the reaction of resin system is sufficient. SEM shows there is no hole or other microdefect in the BT-CH substrates. The D_f of BT-CH substrate is 25% higher than that of BT substrate, and the D_f of BT-CH substrate increases by 6% after thermal oxygen ageing at 153℃ for 4 weeks, which has excellent thermal oxygen ageing resistance.

In order to solve the problem of poor interaction between black shale (BS) and coupling agent in the application process of polymer filler, and the strong odor of sulfur-containing elements during the processing, BS was processed by calcination, the effect of calcination on the composition and morphology of BS was analyzed by XPS, FTIR, and SEM. Then calcinated BS/high density polyethylene (HDPE) composites were prepared, the thermodynamic, mechanical, and electrical properties of the composite materials were tested. The results show that after calcination, the organic matter and pyrite in BS are removed, and the molar ratio of carbon atom in BS decreases from 35.95% to 6.98%, while that of sulfur atom is no longer detectable. The shale maintains a layered structure and has lamellar fragmentation, and the spacing between shale strata is slightly reduced. The impact strength of calcined BS/HDPE composites are significantly higher than that of natural BS/HDPE, because there is a large amount of interfacial bonding between calcined shale and HDPE, while natural shale and HDPE are completely separated. The volume resistivity of the calcined BS/HDPE composites maintains at 4.79×10¹⁶ Ω·cm or higher than that, it is showed the addition of calcined BS has little effect on the dielectric properties of the composites, so that they have good electrical insulation properties.

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.

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.

Under high voltage DC electric field, the particles and defects on the surface of epoxy resin will distort the local electric field and form a non-uniform electric field, and that will induce surface flashover. Most of the existing epoxy resin surface modification schemes focus on the uninformity of treatment, which has limited improvement on the voltage resistance under non-uniform electric field. In this paper, a simulation study was carried out on non-uniform electric field, and the gradient modification scheme was designed according to the characteristics of the electric field. The plasma fluorination modification technology was combined with the concept of gradient insulation, and the plasma step gradient fluorination modification of epoxy resin was realized on the basis of traditional fluorination modification. The results show that the surface morphology, chemical composition, and electrical properties of epoxy resin exhibit a step gradient distribution after plasma step gradient fluorination. Moreover, plasma step gradient fluorination can not only reduce the maximum surface field strength of epoxy resin, but also regulate the dynamic behavior of interface charge, and greatly improve the surface flashover performance of epoxy resin, the improvement effect is better than that of plasma uniform fluorination.

In order to explore the internal mechanism of the difference in space charge characteristics of epoxy based materials used for insulation support in ultra-high voltage power equipment, the dynamic characteristics of space charge of epoxy resin and micro-alumina/epoxy composites under different electrical and thermal environments were studied, and the trap distribution characteristics were discussed. The results show that the space charge distribution of epoxy resin and its composites exhibit obvious temperature characteristics and field strength characteristics. Under high temperature and high electric field strength, space charge is more easily injected from electrodes and migrates in the samples, and the amount of trapped charges increases. The high thermal conductivity of alumina fillers at high temperatures makes charge dissipation faster,and the charge accumulation of alumina/epoxy composite material is improved. At high field conditions, alumina/epoxy composites are more likely to accumulate homopolar charges than epoxy materials, the trap density of alumina material is smaller, resulting in a greater degree of charge accumulation and field strength distortion inside the sample under the same conditions.

In recent years, ablation failure of high-voltage cable buffer layer occurs frequently. In order to solve the problem, this paper established a simulation model for XLPE cables and studied the electric field distribution characteristics of buffer layers under different resistivity. Based on the fault mechanism, a buffer layer repair scheme and a full set of on-site repair process were proposed. Repair tests were conducted on 220 kV high-voltage cross-linked polyethylene fault cables with a length of 1.2 m and 6 m, respectively. The repair effect was evaluated from the perspectives of contact resistance and capacitance current. The results show that with the increase of volume resistivity of the buffer layer, the electric field distortion between the buffer layer and the aluminum sheath is serious, which is easy to cause partial discharge and lead to cable failure. With the decrease of volume resistivity of the buffer layer, the electrical connection between the buffer layer and the aluminum sheath gradually recovers, and the electric field distribution tends to be uniform. After the injection of conductive repair medium, the resistance between the buffer layer and the aluminum sheath decreases by 41.67%, indicating that the electrical connection performance between the buffer layer and the aluminum sheath has been restored.

In order to study the ageing characteristics of stator bar insulation for pumped storage generator set, VPI stator bar for 18 kV pumped storage generator stator was taken as research object, thermal ageing test at different temperatures and different periods was carried out, its physical and chemical properties, thermal properties, and mechanical properties were analyzed, and the change rule of material properties before and after thermal ageing was studied. The results show that during the thermal ageing process, the composition change of epoxy resin in the insulation is the main reason for the change of its microstructure, thermal properties, and mechanical properties. There is a high coincidence between the measured results of physical and chemical properties, thermal properties, and mechanical properties.