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.

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.

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.

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.

In this study, 4,4ʹ-diaminobenzanilide (DABA), 2,2ʹ-dimethyl-[1,1ʹ-biphenyl]-4,4ʹ-diamine (m-TB), dianhydrides pyromellitic dianhydride (PMDA), and 4,4ʹ-oxybisphthalic anhydride (ODPA) were used as raw materials, and a polyimide (PI) film for oganic light emitting diodes (OLED) flexible substrates was successfully synthesized. The results show that when the molar ratio of diamine to dianhydride is 0.990, the feeding time is 120 min, the reaction temperature is 0-30℃, the stirring speed is 200-250 r/min, and the reaction time is 240 min, the gel amount during the synthesis of polyamide acid is small, and viscosity can meet the requirements of industrial synthesis. After thermal imimization at 400℃, the glass transition temperature of the polyimide film is 450℃, the 1% weight loss temperature is 554℃, the thermal expansion coefficient is 4.1×10^-6 K^-1, the tensile strength is 326.9 MPa, the tensile modulus is 9 572.8 MPa, the electric strength is 623 kV/mm, and the dielectric constant is 3.251, which meet the industrial application requirements of OLED flexible substrate.

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 study the effects of compression molding and extrusion molding on the dielectric properties of nanocomposites, these two molding methods were used to prepared the crosslinked polyethylene/organic montmorillonite (XLPE/OMMT) nanocomposites, respectively. The effects of the interlayer spacing change of OMMT in different composites on the resistance-temperature characteristics, dielectric constant, dielectric loss, and electric strength of the composites were discussed. The results show that the force field effect during the molding process can affect the intercalation dispersion effect of OMMT. The tensile stress during extrusion molding makes the OMMT sheets in the sample orient along the tensile direction, and form a regular arrangement unit, which hinders the migration of carriers, thereby improving the resistance-temperature characteristics of the sample. The movement of polymer molecular segments is lim-ited between the oriented lamella, which makes the dipole in the sample decrease, and the dielectric constant and dielectric loss factor decrease. At the same time, the effective intercalation of OMMT and the hybrid structure formed by the polymer cause diffuse reflection of electrons, extending the electron motion path, and improving the electric strength of the extruded sample.

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.

In order to solve the problem of algae adhesion on the insulator surface, a self-healing algae resistant coating suitable for external insulation of power equipment was prepared, and the thermodynamic properties, mechanical properties, algae resistance, self-healing properties, and electrical properties of the coating were tested. The results show that when the frequency is 50 Hz, the algae resistance, mechanical properties, dielectric and electrical properties of the self-healing algae resistant coating with a mass fraction of 0.5% of anti-algae agent are the best. At the same time, the coating can self-heal micro-cracks, reduce the adhesion of mineral salts and moss spores, and inhibit the growth of moss.

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).