In view of three common defects of 10 kV cables, three-dimensional cable defect models were established and conducted electromagnetic-thermal coupled temperature field analysis to study the transient temperature models of three defective cables. The effects of different operating currents and laying conditions on the temperature of three defective cables were analyzed. The results show that the harm of defects on the cable ranked from high to low is metal tip defect, air gap defect, and scratch defect. Under the same current carrying capacity, the temperature at the metal tip defect is higher than that at the other two defects. It is determined that the heat dissipation effect of tunnel laying is the best when the cable has defects. The internal temperature of the cable without defects decreases gradually from the core to outer sheath in the radial direction, and the internal temperature field of the cable is distorted under the action of defects. The fitting coefficients between core temperature and outer sheath temperature of the defective cable, and the fitting coefficients between temperature at the defect and the core temperature of cable are both close to 1. The simulation fitting results provide theoretical support for the judgment and identification of cable defects.

TiO₂ nanoparticles surface modified with acetic acid, hexanoic acid, and oleic acid were synthesized via liquid-phase method and used to prepared modified transformer oils. The morphology and surface modification state of the nanoparticles were measured by transmission electron microscope (TEM) and Fourier infrared spectroscopy (FTIR). The positive impulse breakdown voltage and streamer development pattern of the transformer oil before and after modification were tested, and the effect of nanoparticle surface modification on the breakdown performance of transformer oil was studied. The results show that the surface modified nanoparticles greatly improve the positive impulse breakdown voltage of transformer oil, and significantly prolong the breakdown time. Among them, the acetic acid modified nanoparticles have the best modification effect, which increases the impulse breakdown voltage from 84.73 kV of pure oil to 116.42 kV, an increase of 37.4%, and the breakdown time is extended to 1.86 times that of pure oil. The surface modification of nanoparticles greatly increases the shallow trap density in the oil, changes the streamer propagation pattern, significantly inhibits the development speed of streamer, and thus improves the impulse breakdown properties of the transformer oil.

The morphology and particle size of inorganic fillers are key factors that affect the surface voltage resistance of epoxy resin (EP) composites. In this study, the ZnO nanofibers and particle-shaped ZnO with different particle sizes were used to dope and modify epoxy resin to prepared EP composites, and the DC surface flashover performance and charge dissipation rate of the composites were tested. The results show that the doping of ZnO filler can effectively improve the flashover voltage of EP composites, and the improvement effect of fibrous ZnO filler is significantly better than that of particle-shaped ZnO filler. The flashover voltage of particle ZnO/EP increases with the decrease of filler particle size. When the mass fraction of ZnO nanofiber is 15%, the flashover voltage of EP composite increases by 27.1% compared with that of the pure EP. A finite element simulation model was constructed, and the calculation results show that the fibrous ZnO increases the non-uniform coefficient of the internal electric field in EP, and increases the current density of the composites.

The EVA material was modified by electron beam melting irradiation, and the effects of different irradiation does on gel content, mechanical properties, volume resistivity, dielectric properties, breakdown characteristics and molecular structure of EVA samples were studied. The results show that the gel content of EVA sample first increases and then decreases with the increase of irradiation dose. When the irradiation dose is 100 kGy, the gel content reaches 95.7%. Irradiation can reduce the elongation at break of EVA samples, while the tensile strength first increases and then decreases with the increase of irradiation dose. After irradiation, the insulating properties of EVA samples improve to varying degrees, with the increase of irradiation dose, the volume resistivity first increases and then decreases, the dielectric constant first decreases and then increases, and the electric strength first increases and then decreases.

In order to investigate the effect of thermal treatment on the dielectric relaxation of EP, a EP sample was prepared and conducted thermal treatment at 210℃/48 h. The changes of chemical structures, glass transition temperatures, thermal decomposition parameters, volume resistivities, and dielectric relaxation of the EP before and after thermal treatment were studied. The results show that the thermal treatment does not change the chemical structures and thermal decomposition temperatures of the EP, but the glass transition temperature decreases from 134℃ to 108℃. Furthermore, the dielectric constant of the sample increases after thermal treatment, with a smaller increase at high frequency (10⁶ Hz) and a more significant increase at low frequency (10^-1 Hz).

The circuit breaker nozzle is an important operating insulation component, which has a decisive impact on the opening and closing of circuit breakers. In order to strengthen the quality control of nozzle, the testing conditions of the nozzle material performance were studied. Comparing the tensile property test results of the nozzle material samples with different sizes and different tensile rates, it is found that the dispersion of tensile strength measured with smaller samples and faster tensile rates is smaller. Comparing the electric strength test results of the nozzle material samples under different voltage boosting modes, it is found that the dispersion of electric strength measured by 20 s stepwise voltage boosting mode is smaller. According to the test results, a more reasonable test condition for mechanical strength and electric strength of nozzle materials is selected.

Dry reactors are widely used due to their advantages of stable parameters and small losses. However, with the wide application of dry reactors, related accidents occur frequently, among which the turn-to-turn fault is the most common. In this paper, the causes and mechanisms of turn-to-turn faults of dry reactors were briefly summarized. Then, the research status of turn-to-turn insulation condition monitoring of dry reactors at home and abroad in recent years was reviewed from different perspectives. Finally, based on the deficiencies in the researches, the development trend of turn-to-turn insulation condition monitoring technology for dry reactor was prospected.

Electrical equipment filled with sulfur hexafluoride (SF₆) may experience overheating or discharge when there are internal insulation defects, which will cause SF₆ to decompose and produce some gaseous by-products. By testing the type and concentration of these by-products, we can determine whether there were insulation defects in electrical equipment and the type and severity of these defects. As an important tool of gas detection, gas sensor had been paid more and more attention in the gas detection method of insulation defects. In this paper, the method of detecting SF₆ decomposition products by using gas sensor was reviewed, the dissociation process of SF₆ and the generation path of characteristic gas were introduced, and the gas-sensitive principle, advantages, and disadvantages of the sensor used for detecting SF₆ decomposition characteristic gas were described in detail. The algorithm for diagnosing insulation defect using characteristic gas information was mainly discussed, and the development direction of using sensors to detect gas decomposition components for insulation defect diagnosis was prospected.

When detecting the oil-paper insulation status of transformer based on frequency domain dielectric response (FDS), the nonlinear changes in FDS of oil-paper insulation will affect the accuracy of insulation assessment. Therefore, it is necessary to study the nonlinear changes in the FDS of oil-paper insulation with different ageing degree. The multiple sets of oil-paper insulation models with different ageing degree were prepared in laboratory, and the nonlinear FDS of oil-paper insulation were tested at different temperatures. The results show that the larger the test excitation amplitude, the more significant decrease in the low-frequency range of FDS curve. As the testing temperature and ageing degree increase, the characteristic frequency range of the dielectric loss factor curve showing non-linear changes moves towards the high-frequency direction. On the basis of the modified Davidson-Cole model, the shape parameters in the model were obtained by curve fitting calculation, and then the equivalent circuit model based on the transfer function was established. The nonlinear variation of the impedance modulus of oil-paper insulation was simulated and calculated. According to the simulation results, the circuit parameters of various impedance models are closely related to the nonlinear changes of the dielectric properties of oil-paper insulation, while the change of impedance makes the curve change in the corresponding frequency range.

Composite insulators are widely used in the field of power grid because of their superior performance. At present, due to the increase of the number of birds, the situation of bird pecking composite insulators is becoming increasingly serious, and the insulator structure is damaged after bird pecking, which will cause power grid line faults. Therefore, this paper studies the effect of bird pecking damage on the performance of composite insulators, and provides reference for power grid operation and maintenance management. Firstly, the mechanical and electrical properties of composite insulator after bird pecking were analyzed by experiments. Then, the effects of different damage proportions and different damage number on the surface electric field strength and pollution flashover voltage of composite insulators were studied by artificial simulation of bird pecking umbrella skirt damage. Finally, the electric erosion test, acid immersion test, and thermal ageing test of composite insulator sheath were carried out to evaluate the effect of sheath damage on the properties of composite insulator. The results show that the structure of the composite insulator is damaged after bird pecking, and its electrical properties, mechanical properties, and anti-fouling properties will be affected. At the same time, after the sheath is damaged, under the joint action of many factors such as local field strength, moisture, acid, discharge heat production, and mechanical stress, the core rod material deteriorates and degrades, the mechanical properties of the core rod decrease, and there is a risk of abnormal fracture of the composite insulator.