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.

This paper introduces the research and application of polymer insulating materials in power module packaging, including silicone gel, epoxy potting adhesive, epoxy molding compound, plastic frame and other materials, and their performance indicators and research status at home and abroad were elaborated. Finally, the application direction of polymer insulating materials in power module packaging was prospected, including optimizing the use process, improving the stability and insulation performance, developing materials with temperature shock resistance, low linear thermal expansion coefficient, and high dielectric strength and studying new applications technology.

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.

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.

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 order to study the ageing process of composite insulator silicone rubber in the hot and humid climate in the southern region, we conducted 300 h, 500 h, and 1 000 h salt spray ageing tests on silicone rubber in the laboratory. The concentration of small molecule groups on the surface of silicone rubber with different degrees was detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the ageing mechanism was analyzed combing the hydrophobicity and scanning electron microscope test results. The results show that Si⁺, C₂H₅⁺, SiCH₃⁺, SiC₃H₉⁺, H^-, CH^-, O^-, and OH^- were detected on the surface of silicone rubber. The hydrophobicity of silicone rubber is positively correlated with the content of small alkyl molecules. The content of small alkyl molecules on the surface of silicone rubber is consumed by drip washing of salt spray, which lead to the decrease of hydrophobicity. In the salt spray atmosphere, oxidation and hydrolysis reactions are reacted on the surface of silicone rubber, which results in the broken of Si-O and Si-C bonds, and Si-OH bonds are formed. The hydroxylation lead to the collapse of silicone rubber three-dimensional network structure and the decrease of polymerization degree. The gases such as H₂ and CH₄, generated by the ageing reaction, would form voids on the surface of silicone rubber, which would cause powders and cracks on the surface of silicone rubber.

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.

In this paper, the low-temperature plasma was generated by DBD test platform, and the polyimide (PI) nanocomposite film was modified by the low-temperature plasma. The surface morphology, chemical bond structure, surface conductivity, and corona resistance of the nanocomposite film before and after the low-temperature plasma modification were tested to study the change law of the film surface characteristics. The results show that after surface modification, the nanocomposite film surface becomes rough gradually, and there are micropores and discontinuous protrusions appeared. Polar oxygen-rich groups were introduced on the surface by plasma modification with appropriate modification time. With the increase of modification time, the contact angle decreases, the surface energy and surface conductivity increase, and the corona resistance life increases at first and then decreases. When the low-temperature plasma modification time is 10 s, the corona resistance life of the modified nanocomposites film is 15.7% higher than that of the unmodified nanocomposites film. After modified by the low-temperature plasma, the nanocomposite film has more uniform surface than the pure PI film, and the modified nanocomposite film has the characteristics of small surface energy and large surface conductivity. The large surface conductivity will accelerate the dissipation speed of surface charge of the nanocomposite film, avoid the surface discharge produced by the concentration of local field strength, thereby improving the corona resistance life of the film. To obtain the same modification effect, the nanocomposite film need longer low-temperature plasma modification time than pure PI film.

In order to realize the detection of surface discharge by the temperature sensor inside the composite insulator sheath, we used silicone rubber plate as research object, and established a thermal model to realize the indirect calculation of surface temperature on the silicone rubber plate based on internal temperature. Firstly, according to the heat transfer theory, a thermal model of silicone rubber plate was established. Considering the influence of nonlinear factors in the process of atmospheric convection, the air convection index n was introduced to modify the model, and the solution method of convection heat transfer coefficient h was proposed. Then, temperature rise tests were carried out to simulate the heating condition of silicone rubber plate surface, and the temperature data of the upper and lower surfaces of silicone rubber plate were measured. The measured value of upper surface was compared with the calculated value of model. The results show that the relative error of the steady-state temperature of silicone rubber plate surface calculated by the model based on internal temperature is less than 10%, which meets the accuracy requirement.

The contamination of DC silicone rubber insulator has an important influence on its insulation performance and service life, and the adverse effects of swelling effect under the insulation cleaning agent is the key issue to be solved. The volatilization rate of two kinds of electrified cleaning agent, the swelling and hydrophobicity of silicone rubber before and after cleaning by different cleaning agents were studied, and the corresponding mechanism was discussed. The results show that the volatilization rates of No.1 (fast volatilization) and No.2 (slow volatilization) electrified cleaning agents at 25℃ are 1 095.78 g/(h·m²) and 108.01 g/(h·m²), respectively. The swelling index of silicone rubber increases with the increase of time, it reaches saturation after 10 h, and the swelling index of the saturated silicone rubber are 55% and 130%, respectively. The hydrophobicity of silicone rubber is weakened by No.1 cleaning agent, and the contact angle decreases by 14% after soaking for 10 min. The hydrophobicity of silicone rubber is enhanced by No.2 cleaning agent, and the contact angle increases by 6% after soaking for the same time. Therefore, the cleaning agent with excellent volatility can reduce the adverse effect of swelling on the silicone rubber insulators, and can provide basis and reference for the electrified cleaning of silicone rubber insulation equipment.