In order to develop an on-line monitoring technology for cable insulation status, we analyzed the harmonic components of resistive current by simulating the metal spike in XLPE cable insulation, which provided theoretical and experimental support for cable insulation diagnosis based on the harmonic components of resistive current. Firstly, the conductivity characteristics of XLPE were simulated and theoretically analyzed based on the jump conductivity model of polymer. Then, a simulation model of metal spike defect in XLPE was established, and the harmonic components of resistive current density under different needle curvature radius and needle plate spacing were simulated and analyzed. Finally, three kinds of XLPE metal spike defect samples with different specifications were made, and confirmatory experiments were conducted under the conditions of 30 μm of needle tip curvature radius and 2 mm of needle plate spacing, 90 μm of needle tip curvature radius and 3 mm of needle plate spacing, and 30 μm of needle tip curvature radius and 3 mm of needle plate spacing. The results show that there is metal spike defect in XLPE insulation, due to the sharp increase of local electric field strength, the conductivity characteristics of the insulation material will repeat between the Ohmic and non Ohmic regions with the change of AC voltage waveform, resulting in the distortion of resistive current waveform and the addition of higher-order harmonic components. When there is metal spike defect in XLPE insulation, there are obvious 3rd and 5th harmonic components in the resistive current, which constitutes the main components of resistive current harmonic component. As the severity of metal spike defect increases, the harmonic distortion rate of resistive current and conductivity distortion rate increase significantly, and the harmonic distortion rate can be used as a characteristic quantity to judge the severity of defect.

To investigate the possibility of using black shale as a filler in the plastic industry, the composition and morphology of black shale in Guilin area were studied. It was found that black shale has nano layered structure, and was mainly composed of silica, K-feldspar, and organic carbon. The black shale/HDPE composite were prepared by modifying black shale with different coupling agents and surfactants, and their mechanical properties, morphology, volume resistivity, and dielectric constant were studied. The results show that aluminate coupling agent and sodium dodecylbenzene sulfonate can improve the compatibility between shale and HDPE. When the shale filling amount is 50 phr, the tensile strength, impact strength, and volume resistivity of black shale/HDPE composite reduce. The tensile strength remains at 23.47 MPa, the maximum impact strength is 6.39 kJ/m², and the volume resistivity can also be maintained above 10¹⁴ Ω·cm, maintaining good mechanical properties and insulating properties.

In this paper, the effect of electrical parameters of the semi-conductive layer on the surface electric field distribution of post insulator used in substation was calculated and analyzed by COMSOL. The results show that the semi-conductive layer can weaken the maximum electric field caused by water droplets, wet pollution, and dry pollution to different degrees, and the wet pollution is the most significant, with the electric field decreasing amplitude of 41.58%. Coating semi-conductive layer at the high voltage terminal has a significant improvement effect on the electric field, and the maximum decreasing amplitude of surface maximum electric field is 14.5% compared with not coating semi-conductive layer. When the high and low voltage terminals are coated by semi-conductive layer with the best relative dielectric constant, the comprehensive balance of electric field improvement is better. In the normal range of porcelain electrical parameters, the optimal electrical parameters of semi-conductive layer are universal, the relative dielectric constant of the optimal semi-conductive layer at high voltage terminal is 22, and the relative dielectric constant of that at low voltage terminal is 12. In addition, the resistivity of the semi-conductive layer at high and low voltage terminals should be at least greater than 1×10⁷ Ω·m and 6×10⁷ Ω·m, respectively, and the maximum electric field will be less than the case without semi-conductive layer.

The study on the gas production law of stator bar for hydrogenerator under high temperature and partial discharge can provide a basis for insulation ageing monitoring of hydrogenerator on the basis of decomposition gas method. Aiming at the stator bar used in hydropower station, a high temperature pyrolysis experimental platform was built to study the pyrolysis gas of stator bar at 100, 120, 150 and 250℃. A partial discharge experimental platform of stator bar was established to study the ozone generation law of stator bar under partial discharge. The results show that CO and CO₂ are suitable used as the early characteristic gases of stator bar with high temperature fault. When there is partial discharge on the stator bar surface, the ozone concentration is related to discharge voltage and time. Under the same discharge condition, the ozone concentration rate generated by semi-conductive silica gel is higher and it has stronger corona resistance. Filling stator slot with semi-conductive silica gel is beneficial to the safe operation and on-line monitoring of stator bar.

In order to study the effect of antioxidant types in transformer oil on the thermal ageing performance of insulating paper, antioxidants T501, T531, and DBP were added to the insulation system composed of naphthenic mineral oil and insulating paper, and the antioxidant mass fraction was 0.4%. The heat ageing test was carried out at 130℃ for 600 h. The moisture and furfural content in the insulating oil, the moisture content and polymerization degree in the insulating paper were determined every 120 h. At the same time, the aged insulating paper was characterized by FTIR, XRD, SEM, and EDS. The results show that the addition of antioxidant T501 and T531 have little effect on the deterioration of insulating paper, and the deterioration of insulating paper in the oil with antioxidant DBP is aggravate in the late ageing stage. Since the antioxidant T531 has a combination of neutralization and hydrolysis, it inhibits the degradation process of cellulose, and the ageing degree of T351 insulating paper is the lightest.

A thermochromic microcapsule epoxy resin composite insulation material (TEP) was prepared, and its power frequency permittivity (ε_r), dielectric loss factor (tanδ), and DC conductivity (σ) were analyzed in this paper. The results show that the temperature characteristic of dielectric constant of composite insulation material has an infelction point at 70℃. When the temperature is lower than 70℃, εr increases rapidly with the increase of temperature. When the temperature is higher than 70℃, the change rate of εr with temperature decreases significantly. The tanδ decreases significantly when the temperature is 50-70℃. The addition of thermochromic microcapsules can effectively reduce the DC conductivity of composite insulation material. In the thermochromic temperature range of 50-70℃, the solid-liquid phase transition occurs inside thermochromic microcapsules, which is the main reason for the special temperature characteristics of ε_r and tanδ. In the solid-liquid phase transition process, the molecular activity of the core material in microcapsule increases gradually, and the resistance that it needs to overcome in the orientation polarization with the external electric field decreases, resulting in the rapidly increase of ε_r and the significant decrease of tanδ with the increase of temperature. When the core materials of microcapsule are fully transformed to liquid state, its molecular activity decreases with temperature, leading to the significant decrease of ε_r with temperature.

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.

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 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 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.