Temperature is an important factor that affects the insulating property and the charging state of internal charging effect of insulating materials forspacecraft. In this paper, the change rule of bulk resistivity of substrate materials for satallite circuit board at different temperatures was measured by three-electrode method, on this basis, the effect of temperature on the surface charging potential and internal maximum electric field of insulating materials was simulated and analyzed by using DICTAT program. The results show that in the temperature range from -50℃to 60℃, the bulk resistivity of substrate material decreases with the increase of temperature, and its variation amplitude is more than two orders of magnitude. At the same time, the surface charging potential amplitude and internal electric field intensity of the substrate material increase with the decrease of temperature, and there is a great risk of electrostatic discharge when the temperature is lower than 0℃.

In order to clarify the influence rule of flow velocity of transformer oil on the migration and distortion of suspended bubbles in oil under complex electric field, we analyzed the migration path and distortion degree of bubbles at different flow velocity by numerical simulation. The results show that when the oil flow velocity is lower than 0.24 m/s, the shape of bubble changes periodically, and the change frequency is about 100 Hz. The oil flow velocity is positively correlated with the offset distance form the high-pressure cone, the distortion rate, and the inner maximum electric field intensity of the bubble.

In order to study the causes of dehydration of silicone oil for high voltage cable terminal in closed environment, and investigate its characterization parameters after deterioration, we built an experimental platform with closed environment for thermal ageing and electrical ageing, and tested the physical, chemical, and electrical properties of silicone oil under different ageing states. The results show that both thermal ageing and electrical ageing can cause the dehydration of silicone oil. The thermal ageing at 90℃ and low energy partial discharge have less effect on the deterioration of the physical, chemical, and electrical properties of silicone oil, while the intermittent spark discharge and continuous arc discharge have great effect on that. The breakdown voltage, dielectric loss factor, and volume resistivity have larger correlation with the water content, so that they can effectively represent the deterioration degree of silicon oil.

In order to further improve the insulation performance of meta-aramid paper, we modified nano-TiO₂ by four kinds of silane coupling agents KH550, KH560, KH580, and KH151, respectively, and then prepared modified nano-TiO₂/PMIA composite paper. The influence of coupling agent types on the electrical properties of composite paper, including electrical strength, bulk conductivity and charge-trap characteristics were mainly studied. In addition, the changes in thermal and mechanical properties of different paper were also concerned. based on the molecular dynamic method, the TiO₂-PMIA interface grafted with different silane coupling agents was simulated, and the improvement effect of silane coupling agents on the filler-matrix interface was expounded. The results show that with the electrical insulation performance as the main concern index, the modification effect is ranked as KH550, KH151, KH560, KH580 from the optimal order. The suitable type of silane coupling agent can effectively improve the dispersion of nano-fillers in the matrix, enhance the breakdown voltage and volume resistivity of composite materials, and maintain the temperature resistance and mechanical strength of PMIA fibers.

In this paper, a novel semi-interpenetrating network material PVP/p(HEMA-co-BA) was synthesized by free radical polymerization of 2-hydroxyethyl methacrylate (HEMA), butylacrylate (BA), polyvinyl pyrrolidone (PVP), and host-guest interaction complex which was synthesized by recognition and free radical copolymerization using cyclodextrin modified aluminium oxide nanoparticles (CD-Al₂O₃NPS) as host molecules and acrylate containing adamantane as guest molecules. The microstructure and properties of PVP/p(HEMA-co-BA) were characterized and tested. The results show that the material has self-repairing property by the interaction of host and guest materials. And the introduction of two reversible non-covalent interactions host-guest interaction and hydrogen bond gives the material excellent shape memory function. With the shape memory and self-repair capability, the material can repair by itself and recover the original property when the distance between the two sections of the crack is large. In addition, PVP/p(HEMA-co-BA) has good thermal stability and can be used at 200℃ in high temperature environment.

When the typical insulation structure of 500 kV transformer based on mineral oil is directly applied to the natural ester insulating oil transformer, there are weak points of insulation that need to be improved. In this study, the safety margin of the insulation structure scheme for mineral oil was improved by increasing the main insulation distance, thickening the winding insulation, and optimizing the distribution of longitudinal capacitance of the winding. A designing scheme of insulation structure for 500 kV natural ester insulation oil transformer was formed, and simulation verification of the main insulation and longitudinal insulation of the new scheme was carried out. The results show that the scheme meets the insulation design requirements, the prototype of 500 kV natural ester insulating oil transformer developed with this scheme has successfully passed all the insulating tests.

Under the effect of high temperature, the oil-immersed paper in operating transformer ages gradually, and its resistivity changes with ageing. To get a more complete understanding of the various factors except water that affect the resistivity of oil-immersed paper during the ageing process, at first, we conducted accelerated thermal ageing on the paperboards in vaccum to prepare samples with different degrees of polymerization (DP). Then the water content in the samples was controlled strictly, and their resistivity was measured in vacuum to explore the influence of DP on their resistivity. After that, the paperboards with different DP were immersed in mineral oil with different resistivity to explore the influence of the resistivity of oil on that of oil-immersed paperboard. Finally, the oil-immersed paperboards were accelerated aged, and the change of their resistivity after ageing was observed. The test results show that the resistivity of paperboard slightly increases after ageing, and the increasing trend is partially offset after inmmersing in oil, but there is no significant effect law of oil with different resistivity on resistivity of oil-immersed paperboard. When the water content is simmilar, the resistivity of oil-immersed paperboard decreases significantly with the increase of ageing products. It is concluded the decrease in resistivity of oil-immersed paperboard during ageing is caused by the gereration of polar substances such as water, acid, furfural, and so on. There is quantitative relationship between DP and the resistivity of oil-immersed paperboard.

Aimed at the insulation deterioration of movable cables caused by the tensile force in practical use, we mainly study the effect of the different tensile degree on the insulating properties of ethylene propylene diene monomer (EPDM) insulation based on polarization and depolarization current (PDC). A tension device was designed to measure the PDC and surface potential decay of EPDM under the tensile state, and the influence of tensile ratio on the insulating properties of EPDM was analyzed form the perspective of DC conductivity and trap energy level distribution. The reason for the change of insulating properties of EPDM under tensile state was explained on a micro level. The results show that there is a threshold value of the effect of tensile ratio. When the tensile ratio is lower than 1.4, the PDC decreases with the increase of the tensile ratio. When the tensile ratio is higher than 1.4, the PDC increases with the increase of the tensile ratio. When the tensile ratio increases from 1.0 to 1.4, the decrease of trap numbers leads to the decrease of surface potential decay rate. When the tensile ratio increases from 1.4 to 1.8, the increase of shallow trap numbers promotes the dissipation and migration process of charge, which increases the surface potential decay rate. The influence of tensile stresses on EPDM insulation can be divided into three stages: the amorphous state, elastic deformation stage, and inelastic deformation stage.

The interface charge characteristics of oil-paper insulation under DC voltage is a huge challenge in the design of the insulation structure of converter transformers. The traditional resistance-capacitance (RC) model only considers the interface polarization charges due to the different dielectric constants and electrical conductivity of oil and paper materials, ignoring other forms of charges and their effects on the space electric field. In this paper, based on Kerr electro-optic effect, a non-contact, real-time measurement platform for space electric field characteristics in oil of oil-paper insulation was built. Aimed at the composite insulation structure consist of transformer oil-electrical insulation paper and transformer oil-transformer paperboard, the space electric field characteristics in the oil under DC voltage with different polarity and different amlitude were obtained. The difference between the total interface charge density and the polarization charge density calculated by the RC model was analyzed. The results show that when the electric field intensity in the oil is low, the total interface charge is dominated by polarization charges. With the increase of the electri field intensity in the oil, the difference between the total interface charge density and the polarization charge density calsulated by RC model increases gradually, indicat other forms of charge accumulates and its proportion in total charge increases gradually, the effect of it on the electric field increases gradually.

During the operation of DC cable, the polarity reversal of voltage increases the space charge accumulated in the insulation, and it may damage the insulation . At the same time, the ionic charge generated by the dissociation of impurities such as cross-linking by-products introduced in the actual production process of insulating materials will aggravate the charge accumulation. Therefore, the traditional bipolar carrier transport model was improved in this paper. Considering the influence of impurity charged ions, the distribution of space charge in XLPE during the polarity reversal of voltage were simulated by using the improved transport model, and the influence mechanism of polarity reversal time and electric field intensity on charge distribution was studied. The results show that, on the basis of satisfying the mirror image distribution of space charge before and after the polarity reversal of voltage, the introduction of ionic charge increases the amount of heteropolar charge accumulated near the two electrodes in the steady state. Under the same polarity reversal time and different electric field intensity, the charge distribution law is basically the same, the higher the field strength, the more charge accumulates everywhere.