A polyamide acid was prepared using 4,4′-diamino-2,2′-bistrifluoromethyl benzene (TFMB) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) as raw materials. The azocyclic quinoline (QL) was used to promote its imidization at lower temperature, and the amount of QL, maximum imidization temperature, and curing time were optimized. The imidization degree of polyimide (PI) film was determined by infrared spectroscopy. The results show that when the molar addition of QL is twice that of BPDA, the polyamide acid is only cured for 4 h at 200℃, the imidization degree is more than 99%. After treated at 250℃ for 0.5 h to remove the residual solvent and QL, the thermal stability of the PI is improved greatly, while its light transmittance is basically unchanged. Compared with the PI film imidized at 300℃, the 5% weight loss temperature (T_5%), glass transition temperature (T_g), and tensile strength of the PI film whose imidization promoted by QL decrease slightly, but the elongation at break increases, and the light transmittance at 400 nm increases from 4.5% to 34.4%.

In order to improve the thermal conductivity of polyimide film and maintain its insulating properties, SiO₂ was used to coat AgNWs to obtain AgNWs@SiO₂ core-shell structure. At First, the AgNWs@SiO₂ was dispersed in polyamide acid (PAA) discharge fiber by electrospinning technology, and the heat conduction path and the dispersity of AgNWs@SiO₂ in PI matrix was planned and improved by electrospinning technology, respectively. Then the PAA glue containing AgNWs@SiO₂ was used to impregnate PAA electrospun film, and an E-AgNWs@SiO₂/PI composite film was obtained after thermal imidization. The effects of filler modification and content on the thermal conductivity and insulating properties of the composite films were studied. The results show that when the mass fraction of filler is 25%, the thermal conductivity of E-AgNWs/PI and E-AgNWs@SiO₂/PI composite films is 2.92 W/(m·K) and 2.80 W/(m·K), which are 14.6 and 14 times higher than those of pure PI films, respectively. The dielectric constant of E-AgNWs@SiO₂/PI composite film decreases to below 5, the dielectric loss factor maintains below 0.015, and the volume resistivity increases to 1.79×10¹³ Ω·m.

Dielectric polymer materials with high breakdown, low loss, high flexibility, and low cost play an important role in film capacitor industry. However, low energy storage density and poor thermal stability limit its applications in high-temperature working environments. In this paper, the polyimide-based dielectric energy storage materials and the research methods to improve energy storage property were introduced emphatically, including the influences of the structure and morphology of inorganic fillers with high dielectric constant and high insulation properties or multifunctional composite fillers on the performance of composite films, and the studies on the property of interface micro-area. The future research direction of interface design for high-temperature medium energy storage composite materials was discussed.

The ageing failure of composite insulators in coastal areas has always brought great hidden danger to the safe and stable operation of power grid in coastal areas, and it is also the key and difficult point in the operation and maintenance management of composite insulators. In this paper, the post composite insulators used in substations with different operation years were studied, and the relationship between the hydrophobicity and the operation years was analyzed. The results show that the hydrophobicity is closely related to the high voltage environment, insulator surface orientation, and other factors, and when the operation time of insulators reaches 7 years, the hydrophobicity declines sharply.

This article started from the composition and classification of silicone grease to get access to the performance requirements according to the demand of cable accessories. And then the two typical common grease used in cable accessories was described, including normal silicone grease and silicone fluoride grease. At last, the research status of coated silicone grease used for cable accessories and the selecting method of silicone grease were summarized.

In order to guide the application of composite insulation cross-arm in distribution networks, we carried out 42 h boiling (0.1%NaCl) tests on the sealed and unsealed composite insulation cross-arm according to the requirements of standard GB/T 20142—2006, and studied the influence of high temperature water environment on the performance of the insulation cross-arms treated by the two methods. The water absorption, specified bending load, tensile strength, bending strength, dry power frequency voltage, dry lightning impulse voltage, and breakdown strength of the insulation cross-arms were tested before and after boiling. Meanwhile, the microscopic morphology of the fracture was analyzed by SEM. The result shows that under high temperature water environment, the performance of the sealed cross-arm is better than that of the unsealed one. The specified bending load of all the samples is above 6.5 kN, the lightning impulse withstand voltage is greater than 350 kV, and the tensile and bending strengths is greater than 680 MPa and 1 000 MPa, respectively. The samples show good mechanical and electrical properties.

In order to study the effect of crepe paper on the curing characteristics of epoxy resin, we analyzed the curing process of epoxy resin and epoxy impregnated paper system by differential scanning calorimetry (DSC). The kinetic model parameters of curing reaction were calculated by Flynn-Wall-Ozawa and Malek methods. The results show that both the curing reaction of epoxy resin and epoxy impregnated paper system conform to the autocatalytic kinetic model. The hydroxyl group in the crepe paper has a catalytic effect on the curing reaction, which leads to the decrease of the activation energy of the curing reaction. The restraint of crepe paper leads to the decrease of the frequency factor and reaction order, so that the curing rate of epoxy impregnated paper system is slower than that of epoxy resin. At the same temperature, the curing process of epoxy impregnated paper requires more time.

A kind of composite foam material was prepared by adding hollow polymer microbeads to the organosilicon modified resin, and then the composite foam material was used as the internal filling material for the composite insulating cross-arm. The influence rule of the microbead type and filling content on the density, hydrophobicity, dielectric loss factor, and electric strength of the composite foam material was analyzed. The results show that the filling of organic microbeads can effectively reduce the density of the composite foam, and the density of the sample filled with 920DET40d25 microbeads can be reduced to 0.5538 g/cm³. Because there are more hydrophobic groups in the microbeads, the hydrophobicity of the composite foam material is enhanced. With the increase of the microbead content, the electric strength of composite foam material shows a downward trend, but the insulation strength of all the samples still meets the requirements of the internal insulation material for composite cross-arms. Considering the requirements of the density and insulation strength of the composite foam material, the sample filled with 920DET40d25 microbeads with a mass fraction of 2.5% meets the application requirements.

During the operation of high-frequency transformer, oil-paper insulation bears severe electric and thermal stress, and the insulation system is easy to fail prematurely. In order to study the effect of high frequency pulse voltage on the discharge characteristics of oil-paper insulation, we built a partial discharge (PD) test platform under high frequency pulse voltage to conduct partial discharge tests. The characteristics of partial discharge of oil-paper insulation under highfrequency voltage was studied and compared with the characteristics under power frequency voltage. The results show that under high frequency voltage, partial discharge mainly occurs at the rising and falling edge of voltage, the PD amplitude is much higher than that under power frequency, and there is an frequency-induced inflection point near the frequency of 10 kHz. Moreover, oil-paper insulation is punctured under high frequency impulse. The reason is that the rapid voltage rise rate caused by high frequency changes the local field strength and high frequency electrothermal coupling effect at the defect position, resulting in the change of the partial discharge intensity.

Optical fiber sensing technology has the advantages of anti-electromagnetic interference, small volume, multiplexing, etc. Intelligent on-line monitoring for power equipment by optical fiber sensing technology has become a new trend of power grid development. In this paper, the research progress of several optical fiber sensing technologies in the field of power equipment monitoring were reviewed, including fiber grating sensing technology, scattering distributed optical fiber sensing technology, fluorescent optical fiber sensing technology, and interferometric optical fiber sensing technology. From the aspects of temperature monitoring, strain monitoring, partial discharge monitoring, fiber-optic current sensor, pollution monitoring, and hydrogen monitoring, the application as well as the advantages and disadvantages of different sensing technologies in different power equipment were explained. At last, the development direction of the engineering and networking application of optical fiber sensing technology was proposed.