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.

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).

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.

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.

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.

Space/surface charge accumulation is a potential cause for the decrease of surface flashover voltage of DC GIL insulators. Applying nonlinear conductive coating is an effective method to improve the surface insulation performance. In this paper, a mathematical model was established for the regulation of space/surface charge and surface electric field of insulator by electric field dependent nonlinear con-ductive coating. The nonlinear relationships between the current density of insulating gas and the solid conductivity of insulator and the electric field intensity were comprehensively considered. The internal charge distribution law of insulator under temperature gradient distribution and the influence mechanism of nonlinear conductive coating on the surface charge accumulation of insulator were studied through this model. The results show that the nonlinear conductive coating promotes the dissipation of space charge obviously, and the homopolar charge near the high voltage electrode dominates the surface charge distribution. Due to the improvements of surface charge distribution and tangential electric field, the surface flashover performance improves. The positive charge may accumulate between the insulator and the coating interface, and decrease gradually from the high voltage electrode to the ground electrode.

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.

In this paper, the oil resistance reliability of impregnated resin, enameled flat wire, and aramid fiber paper for oil-cooled motors was studied, and the performance changes of insulating materials after long-term contact with automatic transmission fluid (ATF) under high temperature conditions were investigated. The results show that the insulating materials are greatly affected by the moisture in ATF in the oil resistance test, water and air can promote the hot oxygen ageing of ATF to generate acidic substances, which can accelerate the hydrolysis of material. After conducting high-temperature oil resistance test for 2 000 h, the two impregnating resins, enameled flat wire D and two aramid papers show excellent oil resistance and good reliability.

With the large-scale construction of UHV long-distance power transmission, vegetable insulating oil instead of mineral insulating oil may become the future development trend. In order to analyze the differences and reasons of DC breakdown characteristics of LDPE (low density Polyethylene) under different environments, the DC breakdown experiments of LDPE were conducted in vegetable insulating oil and mineral insulating oil, and the impacts of insulating oil discharge process on the breakdown of LDPE samples were analyzed through simulation. The results show that the electric strength of LDPE in vegetable insulating oil is significantly higher than that in mineral insulating oil. The surface flashover characteristics and breakdown points of the two insulating oils are also different. The field intensity generated by discharge of vegetable insulating oil is small, so the breakdown field of LDPE in vegetable insulating oil is higher. The difference of discharge process of insulating oil is also the reason for the difference of flashover characteristics and breakdown point.