The effects of temperature and DC electric field on the diffusion characteristics of water molecules in nano-SiO₂ modified vegetable insulating oil were analyzed by molecular simulation. The results show that the water molecules in the model is polarized under the influence of strong electric field, and the initial disordered arrangement is rapidly transformed into an ordered arrangement along the electric field. When water molecules are bounded by electric field, the Brownian motion intensity of water molecules becomes weak, and the diffusion strength of water molecules in vegetable oil is weaken. At the same time, the electric field increase the interaction energy between water molecules and vegetable oil molecules, which makes the combination between them more closely, and weakens the influence of temperature on the interaction energy. In addition, the free volume of model is smaller after the application of electric filed, and the peak value of radial distribution is lower in the radial distribution diagram.

In order to analyze the breakdown discharge characteristics of air gap at micrometer scale, a microgap discharge experimental platform was built to study the change of breakdown characteristics of air gap with the air pressure and electrode spacing in the range of electrode spacing between 1-100 μm. When the air pressure or electrode spacing was adjusted to make the breakdown voltage reach the lowest point, it was found that the breakdown voltage curve appeared a plateau, and corresponding to different external conditions, the length range of plateau was different. Through the simulation of microscale electric field, it was found that the electric field at the edge of electrodes was still in a higher range, within the range the self-sustaining discharge can still achieve. The collisional ionization process can reach breakdown between the electrodes through a longer path rather than the shortest distance, so that the breakdown voltage maintained at the lowest point, thus the plateau period was formed. When the electrode spacing was less than 10 μm, the ion-enhanced field emission mechanism was involved in the breakdown, and the lowest point of breakdown voltage continued to decrease from the plateau period. The number density of cathode ions was not only sensitive to the electrode spacing, but also influenced by the external air pressure, and the generated ion-enhanced field would enhance the intensity of field emission and further reduce the breakdown voltage. Combined with the analysis of air pressure and electrode spacing, the traditional Paschen’s law is no longer applicable in the micro-scale range, and the breakdown voltage is no longer determined by the product of the electrode distance d and the pressure p.

The dissolved gas monitoring method in oil is an important method for transformer fault diagnosis and operational status evaluation. A spectral analysis method of gas in transformer oil based on single gas chamber vacuum degassing was presented in this paper, and the principle and structure of the dissolved gas monitoring device in transformer oil based on this method were introduced. Due to the different temperature and pressure in the gas chamber during each detection, temperature and pressure compensation experiments were required, which verified the effectiveness of the temperature and pressure compensation method. Finally, the mixed gas was analyzed quantitatively by the designed device. The results show that the spectral analysis method of gas in oil based on single chamber vacuum degassing designed in this paper has a good effect, which verifies the feasibility of the design scheme. Compared with the common infrared spectroscopy methods for monitoring gas content, this scheme does not require nitrogen as the background gas, reducing the operating costs and improving the automation level of device.

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.

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.

Epoxy resin is used as the main material for insulated packaging of electronic device and motors, it is urgent to improve its thermal conductivity to meet more demanding use requirements. In this research, epoxy resin was modified by filling irregular alumina (i-Al₂O₃), and the effects of irregular i-Al₂O₃ with different volume fraction on the thermal conductivity and other properties of EP were studied. The results show that with the increase of the mass fraction of i-Al₂O₃, the viscosity of the composite mixing system gradually increases, the tensile strength increases at first and then decreases, the thermal stability and thermal conductivity gradually increase. When the volume fraction of i-Al₂O₃ is 45%, the epoxy composite material shows good the overall performance, its thermal conductivity coefficient reaches to 1.44 W/(m·K), which is 585.7% higher than that of pure epoxy resin with the thermal conductivity of 0.21 W/(m·K), at the same time, the volume resistance of the composite remains at the 10¹⁴ Ω·cm quantitative level.

A kind of epoxy resin matrix with high heat resistance was developed, and glass cloth laminates was prepared by high temperature hot-poressing technology using glass cloth as reinforce material. The properties of the matrix resin, cured resin, and the laminates were analyzed. The results show that this cured resin has high heat resistance and good mechanical properties, its glass transition temperature reaches up to 201℃, and the 5% weight loss temperature is 367℃; its tensile strength and flexural strength reaches to 76 MPa and 82 MPa, respectively. The glass cloth reinforced laminates show comprehensive performance, the tensile strength, compression strength, and impacting strength of the laminates is 411 MPa, 480 MPa, and 226 kJ/m², respectively. The flexural strength at room temperature and 180℃ is 633 MPa and 416 MPa, respectively. Moreover, the tracking index (CTI) of the laminates can reach to 550.

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.

In order to study the influence of semi-conductive shielding materials on the charge transport behavior in insulation, we selected three different types of semi-conductive shielding materials made in and out of China to cooperate with the same insulation, and trial-produce a shield-insulation-shield sandwich structure sample by simulating the actual cable structure, and conducted high-field conductance tests and space charge measurements. The results show that the introduction of the shielding layer changes the conduction mode inside the insulation. Compared with the pure insulation sample, the charge injection of the insulation sample with shielding layer increases significantly. The insulation-shielding interface of the imported shielding material sample has a stronger ability to inhibit charge injection, and the charge injection degree is weaker. The measurement of the space charge of each sample shows the impact of charge injection on the degree of space charge accumulation inside the insulation, the space charge accumulation of the shielding material sample made in China is more serious, while that of the imported sample is lower. It is needed to concern the impedance mismatch problem caused by the particularity of the sample structure in the measurement of space charge.

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.