Regarding the internal carbonization creepage defect of composite insulator, a finite element model of electromagnetic and thermal coupling calculation for FXBW-500 large-small-small shed type composite insulator was established, and the influencing laws of defect location and surface pollution on the temperature rise caused by internal carbonization creepage defect in core rod were analyzed. The results show that when there is a local carbonization creepage defect at different positions of composite insulators, the local temperature rise from high to low is high voltage end, low voltage end, and middle end. When there is pollution, the temperature distribution of the carbonization creepage defective insulator does not change significantly, but the maximum temperature rise values of each part all increase significantly, among which the maximum temperature rise of high voltage end increases from 9.3℃ to 18.2℃, and the temperature rise along the surface increases from 2.52℃ to 4.94℃. Although the existence of pollution makes the overall temperature of the insulator rise, it still does not conceal the temperature jump at the defect location. Therefore, when the location of carbonization creepage defects are identified through temperature, the temperature jump can be taken as a reference.

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).

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.

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.

The main insulation of hydro generator stator bar ends is susceptible to thermal ageing due to temperature rise and bombardment of high-energy particles from partial discharges during long-term operation, which would deteriorate the insulation performance and intensify the partial discharges. In this paper, three kinds of typical end defect models were made according to the insulation structure of F-class stator bar for hydropower station, and accelerated thermal ageing tests were carried out at 170℃. The morphological structure and molecular structure of the main insulation samples under different ageing cycles were analyzed by scanning electron microscope and Raman spectrometer to reveal the thermal ageing mechanism of main insulating material, which is epoxy glass mica tape. A partial discharge test platform was set up, the changes of discharge amount, discharge number, and ozone concentration before and after ageing were measured by the pulse current method and ozone detection method, and their influence law on the partial discharge characteristics of end defects were explored. The results show that the accelerated thermal ageing cycle is proportional to the insulating structure change of the main insulating material, and the longer the ageing time, the rougher the surface of the samples. Thermal ageing destroys the molecular chain structure of the epoxy glass mica tape, and the characteristic peak changes of C-C bond and C=C bond on the benzene ring and other aromatic and carbon rings have correlation with the insulation resistance. Thermal ageing has a small effect on the discharge amount and discharge number of the internal air gap, and has a large effect on the discharge number of low discharge amount of the anti-corona layer shedding defects. The saturation concentration and saturation time of ozone in different insulation defect models have large differences, and the changes of ozone concentration of different discharge types before ageing have stage growth characteristics, while the ozone concentration after ageing has no obvious stage growth characteristics.

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.

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.

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.

With the development and construction of offshore wind power, cross-linked polyethylene cables are gradually used in low-frequency power transmission. However, their insulation characteristics after ageing at low-frequency voltage are still unclear. So the insulation characteristics and ageing mechanism of cross-linked polyethylene after ageing at low frequency were studied in this paper. Firstly, cross-linked polyethylene samples were conducted accelerated ageing experiments at voltage frequencies of 20, 35, 50 Hz. Then, the physicochemical and electrical properties of the ageing samples were tested. Finally, the mechanism of voltage frequency on the electrical ageing of cross-linked polyethylene was investigated. The results show that with the decrease of the ageing voltage frequency, the crystallinity of cross-linked polyethylene decreases, the space charge accumulation and conductivity increase, and the AC electric strength decreases. The decrease of voltage frequency makes the ageing degree increase significantly. Combined with the infrared spectroscopy and crystallinity analysis, the decrease of voltage frequency makes the probability of charge into trap and forming hot electron be higher, the electroluminescence effect caused by electron-hole composite is stronger, which causes the increase of polymer molecular chain breakage and cleavage, and then its electric strength is reduced.

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.