In order to investigate the surface discharge process and its microscopic characteristics of glass fiber reinforced epoxy resin composite insulating material, an experimental platform of slant plate electrode was constructed in this paper. Surface tracing and corrosion tests were conducted on samples by a constant tracing voltage method, and the formation mechanism of electric trace was analyzed by combining the Bernoulli equation of ideal liquid. The change of functional groups, surface roughness, and three-dimensional morphology of epoxy resin materials under different stages of tracing corrosion were tested. The results show that the damp and polluted area of insulation composite material is very easy to generate leakage current and discharge, and the most serious corrosion situation always occurs at the bottom electrode firstly. With the increase of tracing corrosion degree on the surface of sample, the epoxy group, hydroxyl group, amino group, aldehyde group in epoxy resin molecular chain gradually decompose, and the carbonyl group decompose not completely after its generation. The surface morphology of the material gradually becomes rough and irregular, the surface roughness shows an upward trend, and the roughness during the explosive period is about 2.8 times bigger than that during the starting period.

In order to investigate the effect of continuous changes in high and low temperatures on the epoxy composite insulation of cable terminals, micron Al₂O₃/epoxy composite insulation samples were prepared in this paper, and thermal-cooling cycling experiments were conducted on the samples. The changes in dielectric properties and degradation mechanism of epoxy composite insulation samples under different number of thermal-cooling cycling were analyzed through the AC breakdown, isothermal surface potential attenuation, and dielectric properties tests. The results show that during the process of thermal-cooling cycling, the cross-linked network of epoxy composite insulation deteriorates gradually under the combined action of high temperature thermal ageing and high and low temperature alternating stresses, the filler gradually separates from the matrix, microcracks and holes appear in the sample, the free volume increases, and the dielectric constant and electric strength continue to decrease. After 750 hours of thermal-cooling cycling, the AC electric strength of the sample decreases by 15.2%, the deep trap density decreases by 41%, the shallow trap density shows a fluctuating trend, and the dielectric loss factor (tanδ) firstly decreases and then slightly increases.

To solve the problem that frequency domain reflectometry (FDR) can only distinguish defect polarity and cannot identify the defect length and type, a defect type discrimination method was proposed on the basis of signal attenuation intensity evaluation in this paper. The difference between the total refracted reflection intensity at each defect and the initial reflection intensity was calculated, and then the defect length and type can be discriminated by comparing the magnitude of difference. Combined with the polarity judgment method, the defect can be subdivided into four types. The results show that the method proposed in this paper can successfully identify the length and type of four common defects in cables, including grounding faults, excessive bending, cable body moisture, and long intermediate joints of cables, and the recognition results are consistent with the simulation modeling results. The defect type discrimination method in this paper can identify the common point defects and segment defects in cables.

In this paper, combined with the application of insulation varnishes on the market in traction motors, the research status and development trend of insulation varnishes for traction motors at home and abroad were reviewed. The insulation varnish systems developed from 180-class (H) diphenyl ether system to the 200-class (N) epoxy anhydride system, and then to the 220-class (R) silicone insulation system, indicating that the insulation varnish system for traction motors were developing towards high heat resistance direction, and the future development and application trend was still high heat resistant insulation varnish systems.

The research on the pyrolysis gas generation law of cable can provide a basis for cable fire early warning. In this paper, a high temperature pyrolysis experiment platform was set up for common cables. The pyrolysis gas generation laws of PVC outer sheath of cables at 75, 100, 120, and 150℃, as well as the pyrolysis gas generation laws of cable internal materials at 185℃ and 225℃ were studied, respectively. The results show that PVC outer sheath of cables has been pyrolyzed at 75℃, and the pyrolysis gases are CO and CO₂. When the temperature is below 120℃, the pyrolysis gas components are only CO and CO₂, so CO and CO₂ are suitable as early characteristic gas components for commonly used cable fires. When the temperature is 150℃, gas components such as CH₄, C₂H₄, C₃H₆, and CH₃Cl appear in the pyrolysis gas, so the CH₄, C₂H₄, C₃H₆, and CH₃Cl can be used as the characteristic gas components of cable overheating faults.

DC cable mainly uses oil-paper and crosslinked polyethylene (XLPE) as insulation, and the conductivity characteristics of the two materials are different, which has a significant effect on the electric field distributions in cable. In this paper, a finite element model was established based on the 500 kV typical DC cable structure, and the thermal-electrical coupled simulation analyses were performed on the oil-paper and XLPE insulated cables. The electric field distribution characteristics in the two insulation under different temperatures and temperature drops were studied, and the influences of the conductivity temperature and electric field coefficient on the field strength distribution were analyzed. The conductivity variations of oil-paper and XLPE insulations among the same temperature and field ranges were compared. The results show that the electric field distribution in oil-paper insulation is affected by the insulation temperature difference in the electric field strength range of 10-25 kV/mm and temperature range of 20-90℃, and hardly changes with the insulation temperature under definite temperature difference, while the electric field distribution in XLPE insulation is affected by both insulation temperature and temperature difference. In addition, the overall conductivity of oil-paper insulation is higher than that of XLPE insulation, and its change amplitude with temperature and field strength is larger, which may be the reason why the electric field inversion in oil-paper cable insulation occurs at a lower temperature difference. For the insulating materials used in HVDC cables, the conductivity temperature coefficient should to be controlled small so as to reduce the temperature sensitivity.

In the process of injection molding of the epoxy insulator on EMU roof, there will be two closing joints on the surface of the umbrella skirt along the vertical direction, the convex edges will distort the electric field near it. In this paper, the influence of the closing joint on the flashover path of the epoxy insulator on EMU roof under wet conditions was studied. Through the spray flashover test, the flashover probability between the closing joint and other parts of the umbrella skirt was compared, the motion characteristics of water droplets on the surface of the epoxy resin umbrella skirt were observed, and the effects of the closing joint on the formation of water band, electric field intensity, and current density distribution were analyzed by simulation. The results show that the flashover channel is easily form at the closing joint, and under the action of electric field, the water band near the closing joint will stretch or even bridge the adjacent skirt. The current density of water band at the closing joint of high voltage end umbrella skirt is more than one time higher than that at other parts of the umbrella skirt. The water band bridging skirt will distort the local electric field, decrease the creepage distance and increase the voltage value borne by the unit creepage distance.

In this paper, tetracyano-benzoquinone dimethane organic small molecules with narrow band gap were introduced, and polyethylene/tetracyano-benzoquinone dimethane composites were prepared by solution blending. The effects of doping content of tetracyano-benzoquinone dimethane on DC breakdown properties, high field conductance and trap distribution properties of the composite were investigated. The results show that the electric strength of the composite increases first and then decreases with the increase of the doping content of tetracyano-benzoquinone dimethane, the addition of tetracyano-benzoquinone dimethane increases the electric strength of polyethylene by a maximum of about 54%, and effectively decreases its conductivity. Trap distribution measurement and quantum chemical simulation confirm that tetracyano-benzoquinone dimethane introduces charge deep traps, enhances the trapping effect of charge carriers, and improves the DC electric strength of polyethylene.

Polyvinylidene fluoride (PVDF)-based polymer has promising applications perspectives in the field of high energy storage density and high pulse energy storage. In this paper, barium titanate (BTO) nanoparticles were doped with polyvinylidene fluoride-chlorotrifluoroethylene (P(VDF-CTFE)) solution, and P(VDF-CTFE)/BTO composite films were prepared by solution casting method. The effects of different BTO doping contents on microstructure, dielectric properties, and energy storage characteristics of the composite films were investigated. Then the BTO was modified by dopamine (DA) to enhance the compatibility between BTO and polymer matrix and improve the dielectric constant and electric strength of composite films. At the same time, on the basis of the "breakdown blocking effect" between the films layers, the laminated composite films were prepared to enhance the energy storage properties. The results show that using the P(VDF-CTFE)/DA@BTO composite film with a DA modified BTO mass fraction of 10% as the interlayer, and the P(VDF-CTFE) as the outerlayer, the prepared PV-BT-PV laminated sandwich composite film has a dielectric constant of 10.44, a maximum electric strength of 362.25 kV/mm, and a charge discharge efficiency of 86.63% at an electric field strength of 500 kV/cm.

In order to improve the accuracy of live detection of line porcelain insulator degradation, the influences of layout methods and deterioration degree on the voltage distribution characteristics of high-voltage AC insulator strings were studied in this paper. Firstly, a finite element simulation calculation model with single voltage distribution of AC 220 kV porcelain insulator strings under different layout methods was established, and the voltage distribution characteristics of the insulator strings were simulated and analyzed. Then, combined with the actual measured voltage distribution of 220 kV AC transmission line insulator string in Shandong province, the consistency between simulation calculation and actual measurement was verified. The results show that the tower type of transmission circuit, the number and layout method of the insulator string, and the position and deterioration degree of the degraded insulator have great effects on the voltage distribution characteristics and deterioration discrimination of the insulator strings. Among them, the maximum distributed voltage difference of different tower types can reach 35%, and the maximum distributed voltage difference of different layout methods can reach 18%. The deterioration situation of insulators at different positions can be judged by the distribution voltage drop ratio.