In order to solve the problem of interface breakdown and surface discharge caused by uneven distribution of electric field of power cable and its terminal insulation, the structural parameters of 35 kV cold shrinkable power cable terminal were optimized to improve its insulation level in this paper. Firstly, the influence of axial length and end radius of stress cone on the terminal electric field distribution was analyzed based on COMSOL simulation software, and the optimal combination of terminal structural parameters was obtained. Then the power cable terminal samples were prepared, and the performance indexes were verified by power frequency AC voltage resistance and partial discharge tests. The results show that the axial length of the power cable terminal stress cone is the main factor affecting the change and distribution of interfacial electric field, and the change of terminal radius has little effect on the terminal electric field. The increase of axial length of stress cone alleviates the interfacial electric field intensity, but it is easy to cause discharge along the surface. The optimal axial length and upper radius of stress cone are 25 mm and 2.5 mm, respectively.

The performance of insulating paper determines the reliability and life of power transformers. In order to ensure the safe and reliable operation of transformers, we combined with domestic and foreign literature and related research results, described the current research status of physical modification technology to improve the performance of insulating paper from the nanoparticle modification and thermal stabilizer modification, analyzed the advantages and disadvantages of the two modification methods, and explored the economic and feasible modification method of cellulose insulating paper for power transformers to essentially improve the reliability of transformer operation.

In order to study the effect of mesoscale crystal morphology of XLPE material on its AC breakdown characteristics and analyze its mechanism, XLPE samples with different crystal morphologies were prepared by controlling the cooling rate of samples during cooling crystallization. At the same time, the crystalline structure and morphology of the samples were characterized and observed by scanning electron microscope (SEM) and X-ray diffraction (XRD), and its dielectric properties were tested by the broadband dielectric spectrometer, three electrode system, and AC breakdown system. Finally, the test results were verified and the mechanism was analyzed by means of simulation. The results show that decreasing the cooling rate can prolong the crystallization time, making the molecular chains regularly arrange and stack to form large-size spherulites with a relatively high crystal area and relatively perfect structure. The improvement of crystal structure makes the relative dielectric constant of the XLPE sample increase slightly, the conductivity decrease, and the breakdown strength and stability significantly improve. The simulation results are consistent with the test results. The perfect crystal morphology of the sample at mesoscale reduces the degree of electric field distortion between spherulites and inhibits the occurrence of partial discharge and breakdown.

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 order to guide the selection of fluorocarbon resin film forming material cured at room temperature in the development of anti-pollution flashover coating, the structure and properties of fluorocarbon resin film forming materials were characterized by FT-IR, AFM, UV ageing, thermogravimetric analysis, contact angle test, volume resistivity and high-voltage capacitor bridge. The results show that the optimal mass fraction of curing agent for FEVE-based type I and type II fluorocarbon resins are 19% and 24%, respectively. Under the optimal curing agent content, the contact angle of FEVE-based type I and type II fluorocarbon resins are 91° and 104°, respectively. After UV ageing for 800 h, the appearance color, hydrophobicity, hardness, adhesion, thermal decomposition temperature, and molecular structure do not change. After 30 min of ultrasonic fog wetting, the AC wet lightning voltage of fluorocarbon resin is about 25 kV, indicating that the FEVE-based fluorocarbon resin has excellent electrical insulation properties and ageing resistance, and is a good base material for the development of antifouling flashover coatings.

Kelvin probe force microscope (KPFM) is an important tool to measure the surface potential of materials with nanometer resolution. Because of its sensitivity to the surface charge of materials, it has been widely used in the research of dielectric charge behavior in recent years. This paper introduced the principle of KPFM, summarized the latest research progress of KPFM applied to charge behavior in dielectrics, focused on the analysis of the diffusion and migration mechanism of surface and interface charges in dielectrics. And the application of KPFM in typical dielectrics such as inorganic materials, nanocomposites, and ferroelectric materials were also reviewed.

Based on the mechanical properties of the accessory silicone rubber material, a mainstream accessory on the market at present were conducted accelerated thermal ageing test, and then the tensile properties and thermal weight loss characteristics of the accessory silicone rubber were tested. The life model of silicone rubber was built based on its breaking elongation retention rate by using Arrhenius formula. The results show that the mechanical properties of silicone rubber decrease after thermal ageing, which is manifested by the increase of elastic modulus and the decrease of tensile strength and elongation at break. When only consider the thermal ageing of silicone rubber material, the theoretical operating life of cable accessories is 13.0–44.5 years.

In order to study the influence of the relative dielectric constant of motor insulation structure on the electric field distribution at different frequencies, this article took the relative dielectric constant of a main insulation structure at different frequencies as a variable to calculate its influence on the electric field distribution of the main insulation sandwich structure in the slot and the notch. At the same time, the optimization measures for the electric field of slot were analyzed. The results show that in the sandwich structure of main insulaton, because the film has a lower dielectric constant, it bears a larger electric field than mica tape. When the relative dielectric constant of the air at the notch is constant, the electric field strength of the air at the notch decreases slightly with the decrease of the relative dielectric constant of the main insulation. The insulating paint in the small gap at the chamfer of the notch iron core can reduce the electric field strength of air; without insulatin paint, the small gap generated by chamfer can produce a larger electric field strength of air. Vacuum potting of the notch can effectively reduce the electric field strength of air at the notch.

Glass fiber reinforced resin polymer (GFRP), which is widely used in high voltage electrical equipment, is easily to be eroded by hygrothermal environment under long-term operation conditions, resulting in insulation deterioration, which affects the safe and stable operation of power system. In this paper, glass fiber was modified by nano SiO₂, and GFRP composites were synthesized by infiltrating epoxy resin. Accelerated hygrothermal ageing treatment was carried out on the composites, and the influence of different concentrations of nano SiO₂ on water invasion and ageing resistance of GFRP was analyzed by experimental test and simulation. The results show that when the mass fraction of SiO₂ is 9.4%, GFRP has the best inhibition effect on water intrusion. At the same time, the addition of SiO₂ can make the GFRP composites maintain high surface insulation properties before and after ageing. In addition, combined with the simulation results, the inhibition effect of SiO₂ on water intrusion of GFRP composites and the influence mechanism of hygrothermal ageing resistance of GFRP are revealed from the molecular scale.