To investigate the influence of the filler network constructed by alumina (Al₂O₃) on the thermal and dielectric properties of polypropylene (PP) composites, this study constructed a finite element model of randomly filled Al₂O₃ fillers, and systematically studied the effects of factors such as filler content, filler particle size, and size matching of binary fillers on the thermal conductivity and dielectric constant of Al₂O₃/PP composites. The results indicate that increasing the filler content can significantly bridge the Al₂O₃ filler, synergistically construct an interconnected thermal conductive network and electric displacement pathway, thereby significantly improving the thermal conductivity and dielectric constant of Al₂O₃/PP composites. For single Al₂O₃ filled PP composites, the thermal conductivity and dielectric constant of composites cannot be effectively enhanced by regulating the size of Al₂O₃ filler. After introducing the multiscale fillers, at the optimized binary filler ratio of 70∶30 (40 μm∶15 μm), the overall thermal conductivity and electrical displacement networks show the dominant skeleton of large-sized filler and the bridging branch of small-sized fillers features, which synergistically contributes to the Al₂O₃/PP composite reach the optimal thermal conductivity (0.55 W/(m·K)) and dielectric constant (5.6).

To explore the thermal mechanical stress distribution of motor insulation structure at high temperatures, we take the insulation structure of organic silicone system as the research object, test its thermal expansion coefficient and elastic modulus at different temperatures, and analyze the influence of thermal stress parameters at different temperatures on the thermal mechanical stress of organic silicone insulation system. The results show that within -50-200℃, the thermal expansion coefficient of insulation structure show a change trend of increases, decreases, and increases again with the increase of temperature, and its value is 0.8×10^-5-1.7×10^-5 K^-1. The elastic modulus increases at first and then decrease with the increase of temperature, and its value is 0.2×10³-3×10³ MPa. The thermal mechanical stress borne by insulation structures increases linearly with the increase of thermal expansion coefficient and elastic modulus. The thermal mechanical stress of insulation structures firstly increases and then decreases with the increase of temperature, depending on the size of thermal expansion coefficient and elastic modulus at different temperatures. The feasibility of testing parameters and simulation analysis was verified through stress testing of the wire rod and motor, and the deviation between simulation value and testing value is within 15%. The simulation analysis results show that at 120℃, the maximum thermal mechanical stress point of motor insulation is located at the slot insulation, and the maximum stress value is 11.37 MPa. After sealing, the maximum thermal stress value of the slot insulation can be reduced by about 45%.

The 110 kV epoxy resin dry type transformer has the phenomenon of flashover in the airway on the high voltage side due to its high electric field intensity. The high voltage side coil of transformer was modeled and simulated by finite element simulation software in this paper, and the standard lightning impulse was applied to verify the lightning impulse. According to the simulation results, the causes of flashover were analyzed and the field strength distribution at the airway was optimized. The results show that the electric field distribution is improved by adding a specific medium to the corresponding area inside the epoxy resin. At the same time, by changing the relative dielectric constant and position of the medium, the maximum field strength at the airway is reduced by 8.75% under the restriction of field strength inside the transformer, which meets the field strength requirement of the high-voltage side airway of the dry-type transformer to inhibit flashover.

To investigate the impact of interface air gap and moisture defects on the multilayer composite dielectric insulation interface of ±320 kV DC cable intermediate joints on their electric field distribution mechanism, a simulation model of ±320 kV DC cable intermediate joint was built, and the electric field distribution of the cable joint with air gap and moisture defects on the multilayer composite dielectric interface region was calculated using the finite element method. The effect of these defects on the electric field distribution of the cable joint were analyzed at no load and load conditions, and their differences under AC/DC electric fields were discussed. The results show that there is significant electric field distortion at the composite dielectric interface of the DC cable joint due to air gap and moisture defects under the action of DC electric field. The multiple of electric field distortion of air gap defects is 9.6 times at no load and 1.7 times at load condition. The electric field strength in the water film defects decrease over 99.9% at both operating conditions. Interestingly, the electric field distortion induced by air gap defects in cable joints at no load is larger than that at load condition, and the temperature differentials across the joint play a role in field homogenization. However, the temperature differentials across the joint induced by moisture at load promote the accumulation of space charge in the joint, which leading to the multiple of electric field distortion at moisture defect bigger than than at no load. Notably, the multiple of electric field distortion resulting from defects in DC cable intermediate joint is bigger than that of AC cables.

High voltage cable is an important part of power supply system. Buffer layer ablation can lead to power cable failure. In recent years, several cable accidents caused by buffer layer ablation have occurred. In order to solve the above problems, a multi-parameter detection method for cable ablation defects was proposed based on buffer layer ablation characteristic gases, temperature and pressure variation. The CH₄, C₂H₆, and C₂H₄ content in the buffer layer was analyzed by Fourier transform infrared spectroscopy. The H₂ content in the buffer layer was measured by electrochemical sensor. The temperature and barometric pressure in the buffer layer were measured by temperature sensor and piezoelectric barometric pressure sensor. The performance of the system was tested by laboratory buffer layer ablation experiment and actual cable detection experiment. The results show that the functionality and accuracy of the system meet the requirements, and the four characteristic gases content, temperature, and pressure can be used as the parameters to characterize the buffer layer ablation defects. The detection period of the system is less than 30 s, and the detection error is within ±10%. The system has advantages in terms of safety, detection speed, and accuracy, which can guarantee the safe operation of power cables.

With the increase of grid capacity and voltage level, the insulating properties of epoxy composite insulation materials is crucial to the safe and stable operation of electrical equipment. Long-term high temperature and high humidity will lead to a serious decline in insulating properties of materials. Nano-SiO₂ was fluorinated (F-SiO₂) by the plasma technology of dielectric barrier discharge (DBD) in this paper, and fluorine-containing groups were successfully grafted on the surface of nano-SiO₂. The high-temperature and humid state of the material was simulated by the wet heat ageing experiment, and the surface flashover, charge dissipation characteristics and trap distribution characteristics of the samples at different ageing stages were tested. The effect of doping F-SiO₂ on the wet heat ageing resistance of epoxy composites was explored, and the inhibition mechanism of F-SiO₂ on the water intrusion was revealed from the molecular scale in combination with MD simulation. The experimental results show that doping F-SiO₂ reduces the saturated moisture absorption of epoxy composites by 16.16%, increases the surface flashover voltage by 13.06%, and can continue to maintain high insulating properties after wet heat ageing. The simulation results show that F-SiO₂ can reduce the free volume fraction of epoxy resin and the mean square displacement of water molecules, and enhance the barrier effect of epoxy composites on moisture. Plasma technology can graft fluorine elements onto the surface of nano-SiO₂, effectively inhibiting the intrusion of moisture and enhancing the surface insulating properties of epoxy composites in a humid state.

To reduce the partial discharge (PD) of the basin-type insulator in gas-insulated switchgear (GIS), reduce the occurrence of insulation faults, and improve the safety and stability of GIS operation, we took the 252 kV basin-type insulator as the simulation analysis object. The basin-type insulators with and without grounding shield ring were conducted simulation calculation by Comsol software, and basin-type insulators with different sizes of grounding shield ring were conducted simulation comparison analysis. The insulating and mechanical properties of the basin-type insulator were further verified through experiments. The results show that adding a ground shield ring in the basin-type insulator can effectively improve the electric field in the wedge air gap region and significantly reduce the partial discharge value of the basin-type insulator.

Air gap defect is one of the common internal defects in GIS, which can cause electric field distortion. The introduction of dielectric functional graded materials can optimize the local electric field of basin insulators. However, under the combined effect of air gap defect and dielectric functional graded materials, its electric field characteristics are not yet known. Therefore, an electric field simulation model of GIS basin insulator with uniform medium and dielectric functional graded materials (ε-FGM) was built in this paper, and the influence of the existence of air gap and air gap position on the electric field distribution of insulators with uniform medium and ε-FGM was discussed. The results show that the introduced dielectric functional graded materials have a relatively ideal regulatory effect. When air gap defects are doped in a uniform medium, the field strength of air gap near the high-voltage conductor, insulator middle, and grounding shell will significantly increase, and the increase rate is 85.32%, 78.10%, and 68.69%, respectively. The influence trend of air gap defects on the electric field characteristics of insulators with ε-FGM is basically consistent with the influence trend on the uniform media, but from a specific numerical perspective, there is still a certain difference. Air gap defects have a greater impact on the electric field of insulators with ε-FGM. When designing insulators with ε-FGM, special attention should be paid to suppress the air gap defects in medium.

To investigate the influence law and mechanism of polyethylene glycol diglycidyl ether (PEGDGE) on the mechanical and thermal properties of epoxy materials for insulated pull rods, molecular dynamics simulations were used to calculate and analyze the macroscopic properties and microscopic structural parameters of epoxy resin cross-linked systems with PEGDGE mass fractions of 0, 5%, 10%, 15%, and 20% (percentage of epoxy resin mass), respectively. The effect of PEGDGE content on the mechanical and thermal properties of epoxy materials for insulated pull rods was summarized, the influence mechanism was elucidated from the perspective of system structure, and the calculation results were verified through experiments. The results show that with the introduction of PEGDGE, the glass transition temperature, tensile strength, and bending strength of epoxy resin, as well as the viscosity of castable decrease, while the impact strength of epoxy resin increases. When the mass fraction of PEGDGE is 5%, the material shows the best comprehensive performance. PEGDGE molecules with high flexibility increases the free volume fraction, mean square displacement, and the ratio of bulk modulus to shear modulus (K/G) of the epoxy resin system, which enhances the mobility of molecular segments, and leads to the increase of toughness and the decrease of rigidity of the epoxy resin material.

Epoxy resin and its composite materials play a major insulation role in electrical apparatus due to their excellent thermodynamic and electrical insulating properties. With the gradual development of electrical apparatus towards high voltage and high power, as well as the continuous rise of voltage levels, the performance requirements for epoxy insulating materials inside electrical apparatus are increasingly increasing. This paper focused on epoxy resin insulating materials for high-voltage electrical apparatus, and reviewed the current research and application progress from three aspects: formulation composition, curing process, and performance improvement of insulation systems. It was aimed to establish the relationship between the composition, structure, and macroscopic properties of epoxy insulation systems, provide suggestions and prospects for the development direction of domestic epoxy resin insulating materials in the future, and accelerate the localization development of epoxy resin materials for high-voltage insulation.