Oil-paper insulation is the main insulation material for oil-immersed power equipment, and its ageing under long-term complex working conditions will seriously affect the use safety of equipment. Therefore, the accurate evaluation of its insulation status is crucial. Multiple sets of oil-paper insulation models with different degrees of ageing were prepared in this paper, and wide temperature-wide frequency dielectric response tests at different test excitation amplitudes were conducted. Characteristic parameters characterized the ageing of oil-paper insulation was extracted on the basis of Disado-Hill relaxation model. The test results show that as the ageing of oil-paper insulation increases, the full frequency range loss factor curves show two characteristic frequency ranges, which are respectively related to the material conductivity characteristics, turning polarization and interface polarization process. According to the fitting calculation results, it is found that after ageing of the oil-paper insulation, the cellulose structure is damaged, and the number of impurity ions in the dielectric increases, which is manifested at the micro level as enhancing the inter cluster motion within the dielectric and weakening the intra cluster motion. Therefore, the characteristic frequency points in the model move towards higher frequencies. Meanwhile, to accurately obtain the ageing state of oil-paper insulation, a quantitative characterization relationship between model characteristic parameters and insulation ageing was constructed by eliminating the influence of test temperature and excitation amplitude. The research results provide theoretical support for the evaluation method of insulation ageing state of oil-immersed power equipment based on frequency domain dielectric response on-site detection technology.

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 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.

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.

After the occurrence of line tree barriers, it is difficult to successfully reclose the line, which can easily cause line shutdown. There are multiple major power outages caused by tree barriers both at home and abroad, but the electric field distribution characteristics and discharge mechanism of insulated conductors with different types of tree barrier are still unclear. Therefore, electrostatic field models of insulated conductors with different types of tree barrier were established on the basis of finite element theory in this paper, and the erosion mechanism of tree barrier discharge was revealed according to the obtained electric field distribution and gas-solid discharge theory. The results show that the tree barrier types of insulated conductor are mainly divided into four categories: single side wedge-shaped penetration defects, flat cut defects, double wedge-shaped penetration defects, and critical contact between wood throns and defects tree barrier-wire types. The electric field undergoes distortion at the defects of tree barrier, and the wedge-shaped penetration defects can cause gas breakdown and discharge at the site of tree branch-insulation wire, which poses the greatest damage to the surface of insulation wire and the erosion of tree branches. The field strength at the defect site is affected by the degree of defect and air gap, and the maximum electric field strength of the wood thorn penetrating into the insulation layer is 2.64 times higher than that of the wood thorn penetrating only into the shielding layer. The wind disturbance causes the critical contact between the wood thorn and defect to generate air gap, and its electric field is 2.54 times higher than that without air gap (5.65 kV/mm). The research results provide a theoretical basis for different types of tree barrier defense methods, avoiding the drawbacks of cutting tree indiscriminately.

Insulating oil plays a critical role as a dielectric medium in reactors, and the breakdown voltage is a key indicator evaluating its insulating properties, which is closely related to the quality of insulating oil. In this paper, 155 reactor insulating oil samples were selected for experiments, which included the measurement of breakdown voltage and collection of multi-frequency ultrasound signals after propagation in the oil samples. The relationship between the breakdown voltage and the amplitude-frequency and phase-frequency responses of ultrasonic acoustic parameters was analyzed. A breakdown voltage prediction method was then proposed by combining multi-frequency ultrasound technology with a grey wolf optimizer (GWO) optimized random forest (RF) algorithm. The results show that the GWO-RF model achieves 4.04% of mean relative error and 95.96% of accuracy on the test set, and there is 20.25% of improvement in prediction accuracy compared to the unoptimized RF model. The proposed prediction model, which integrates multi-frequency ultrasound detection and GWO-RF optimization, demonstrates significant feasibility for predicting the breakdown voltage of insulating oil in reactor.

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.

This paper reviewed the research progress on active esters for epoxy curing at home and abroad in recent years, with a focus on the structures of different active esters. By classifying active esters according to raw material sources and ester bond positions, the characteristics and differences of active esters with different structures in epoxy resin curing agents were explored. Finally, the development trend and application prospects of active esters for epoxy curing were discussed.

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.