Curing agent acts as a link of epoxy resin molecular chains, its molecular structure will affect the various properties of epoxy resin. In this paper, the influence of curing agent molecular structure on the thermal properties, polarization properties, charge transport properties, and energy storage properties of epoxy films were comprehensively discussed by adjusting the ratio of alicyclic amine to polyether amine in curing agent. The results show that with the increase of proportion of rigid alicyclic amine in curing agent, the thermal stability of epoxy resin is significantly enhanced, and the dielectric loss is greatly reduced. This is mainly because the increase of rigid groups can effectively restrict the turning of molecular segments and the transporting of charge. Meanwhile, with the increase of ratio of alicyclic amine, the electric strength and charge-discharge efficiency of the epoxy film increase at first and then decrease. The F51/AP1.6 has the most excellent electric strength, energy density, and charge-discharge efficiency under four different ratios of curing agent. This is related to its stable molecular structure, low dielectric loss, and extremely high deep traps density.

The degree of partial discharge in transformer is an important basis to reflect the ageing degree of transformer insulating oil and evaluate the service life of transformer oil. In this paper, six kinds of transformer insulating oil with different water content were conducted partial discharge tests by two different test methods and four electrode arrangements. The influence of different test methods and electrode arrangements on the partial discharge initial voltage was analyzed. The results show that the partial discharge initial voltage is not only related to the physical and chemical properties of liquid dielectric, but also affected by the electrode arrangement, water content, and test methods. The test methods affect the dispersion of test results. The water content would change the physical and chemical properties of liquid dielectric, thereby it affects the partial discharge initial voltage from the aspects of macro dielectric property and micro ionization process. With the increase of water content, the electrode arrangement and test methods have less influence on the partial discharge initial voltage. The main factors affecting the partial discharge initial voltage of insulating oil with different water contents change from electrode arrangement and test method to the physical and chemical properties of insulating oil.

Polluted insulators are easy to discharge or even flashover when the surface is wet to a certain extent, which seriously threatens the safety and stability of power grid. In this paper, in view of three kinds of common insoluble contaminates SiO₂, Al₂O₃, Fe₂O₃, we conducted water absorption tests and insulator flashover tests under different environmental humidity, and the influence of environment humidity on the water absorption and flashover properties of insulators polluted with typical insoluble contaminates were analyzed. The results show that the SiO₂ has the best water absorption property, the Al₂O₃ is followed, and the Fe₂O₃ has extremely weak water absorption property or cannot absorb water absolutely. The moisture absorption rate and saturated moisture content of SiO₂ and Al₂O₃ tend to increase with the increase of environment humidity. In the situation of saturated humidity, the surface contamination of insulators polluted by SiO₂ and Al₂O₃ may be washed away with the dripping process of liquid droplets. The pollution flashover voltage gradient of insulators decreases with the increase of environmental humidity, and this phenomenon is more obvious in low humidity.

Firstly, oil-impregnated insulating papers with different ageing states were prepared, and their breakdown voltages under pulsating DC voltage were measured and compared with AC and DC breakdown voltage. The polymerization degree, moisture content, mesopore distribution, and crack characteristics of oil-impregnated insulating papers were measured to explore the possible influencing factors of breakdown voltage under different ageing states. The results show that the AC breakdown voltage is the smallest, and the pulsed DC breakdown voltage (r=1/5) is the largest before failure of oil-impregnated insulating papers. During thermal ageing process, the breakdown voltage fluctuates occasionally or even increases. Compared to AC breakdown voltage, the breakdown voltage under DC and pulsed DC voltages (r=1/5 and 1/3) shows opposite trends with ageing time. The water content and oil absorption capacity of oil-impregnated insulating papers, and the damage to the paper structure are the reasons causing the breakdown voltage to change with ageing time, but the importance of reasons vary with the ageing state.

The traditional electromagnetic wire appearance defect detection uses manual detection, which is low efficiency and high cost. With the continuous improvement of requirements of motor on the appearance quality of electromagnetic wire, it is necessary to enhance the identification efficiency of electromagnetic wire appearance defects. A visual identity system of electromagnetic wires defects was developed, and the practical application effect of the system was verified. The results show that the defect visual identity system can improve the detection rate of the thin film sintering line appearance defects. By analyzing the statistical types and quantities of defects, the problems of raw materials or the production process problems of electromagnetic wire can be found in time, so as to formulate corrective measures in time and reduce the rejection rate of the thin film sintering line.

In order to better guide the application of composite insulation crossarms, the lightning impulse voltage, wet power frequency flashover voltage, pollution flashover voltage, and pollution snow-covered flashover voltage of the square tube composite insulation crossarm and the square bar composite insulation crossarm were compared and studied through experiments. The results show that the 50% dry lightning flashover voltage of the 10 kV square tube composite insulation crossarms is 388.3 kV, which is higher than that of the square bar composite insulation crossarm (370.0 kV). However, the wet power frequency withstand voltage, pollution withstand voltage, and pollution snow-covered flashover voltage of the square tube composite insulation crossarms are lower than that of the square bar composite insulation crossarms. Finally, the different application scheme of the composite insulation crossarms under different operating environment is proposed.

Aiming at the application requirements of rail transit, we studied and compared the performance of A766 aramid insulation paper and the same types of aramid insulation paper at home and abroad. The results show that the composition and structure of A766 aramid insulation paper and the imported aramid insulation paper are basically the same. The temperature index of A766 aramid insulation paper is 223℃, the oxygen index is 30.2%, the smoke density is 1.4, and the smoke toxicity is 0.875, which meets the HL2 and HL2 of R22 and R23 fire rating standards. A766 aramid insulation paper has higher voltage withstand retention rate after immersion in water, the retention rate of 0.05 mm aramid insulation paper is 83.5%, and the retention rate of 0.13 mm aramid insulation paper is 73.8%. The Shawn’s experiment shows that the thermal oxygen ageing property resistance to copper/aluminum metal conductor of A766 aramid insulation paper is the same as that of the imported aramid insulation paper. Therefore, A766 aramid insulation paper can meet the application requirements of rail transit.

At first, the insulation level of returned cable was analyzed by ultra-low frequency (VLF) dielectric loss test method and microscope observation method. And then, the organic-inorganic composite repair fluid was injected into the cable core through a repair system. After repairing for 24 h, the generated filler was analyzed by scanning electron microscopy (SEM) and infrared spectroscopy (IR), and the insulation level of the cable after repairing was analyzed by VLF dielectric loss test method and breakdown voltage test method. The microscopic test results show that after injecting the organic-inorganic composite repair fluid, the micropores and defects will be filled during the penetration and reaction process of repair fluid in cable insulation layer, both the number and size of micropores in repaired cable insulation are smaller than those in unrepaired sample, at the same time, the hydroxyl absorption peak is reduced significantly. The VLF dielectric loss test results show that the performance indexes of the cable after repairing is enhanced, and the breakdown voltage is improved. It is proved that the organic-inorganic composite repairing technology can improve the insulating properties of field returned cable effectively and prolong the cable insulation life.

In this paper, thermal ageing tests were conducted on the prepared silicone rubber-based flame-retardant transmission insulator samples at 210℃ for different times by high temperature accelerated ageing method, and their performance were tested by scanning electron microscope (SEM), Fourier infrared spectroscopy (FTIR), and contact angle tester. The results show that with the extension of ageing time, the melamine cyanurate (MCA) flame retardant particles in the sample decompose continuously, a large number of pores are formed on the surface of sample, and the infrared intensity of amino and hydroxyl functional groups continues to decrease. The contact angles measured by different solutions show a downward trend, and the erosion of hydrophobicity by the salt solution and acid solution is more serious. The lifetime of samples under the water condition calculated by Hallberg-Peck model and the contact angle is 16.6 years, the lifetime of samples under acid rain conditions is 10.4 years, and the lifetime of samples under seawater condition is 10.2 years.

Partial discharge would accelerate the ageing of power equipment insulation, which is an important monitoring indicator for the condition assessment of power equipment. The research related to partial discharge mainly include denoising of discharge signals, pattern recognition of defect types, equipment status assessment, and fault location of discharge sources. The artificial intelligence can effectively solve the problems of non-linear fitting and optimal solution in partial discharge detection. This paper introduces the detection methods of partial discharge, summarizes the application of artificial intelligence in both denoising of discharge signals and fault location of discharge sources, and points out the shortcomings and solutions in the current research.