In this paper, the physicochemical and electrical properties of oil-paper insulation in the process of surface discharge deterioration under static and flowing oil conditions were studied. The discharge product and moisture of oil-paper insulation were analyzed by infrared spectrometer and micro-water measuring instrument. The multilayer microstructure of oil-paper insulation was analyzed by viscosity tester, X-ray diffractometer, and scanning electron microscope. The conductivity, electric strength, and partial discharge of oil-paper insulation were analyzed by electrical measurement. The multi-type discharge deterioration characteristics of oil-paper insulation in static and flowing oil were compared and analyzed. The results show that the flow of oil slows down the surface discharge deterioration of oil-paper insulation, retards the rise of electrical conductivity and the decline of electric strength, and inhibits the occurrence and development of surface discharge. The surface conductivity determines the difficulty of surface discharge, and its increase results in the statistical distribution of surface discharge times showing a repetitive characteristic of "wave" gradually. Discharge frequency determines the surface discharge deterioration and destruction degree of oil-paper insulation, which is an efficient characteristic quantity to evaluate the deterioration state of oil-paper surface discharge.

In order to solve the prediction problem of water tree density of XLPE cable, an analysis method combining the macro detection data with the micro water tree profile of aged cable was proposed. Two new parameters (carbon and oxygen index and water content index) were proposed to quantitatively describe the changes of EDS and FTIR results in the water tree region. Firstly, the polarization and depolarization current method (PDC) was used to detect the water-tree ageing cables under different experimental conditions. A series of macroscopic parameters such as cable ageing factor, DC conductivity, and 0.1 Hz dielectric loss factor were obtained. Then, the micro parameters of water tree were obtained by microscopic observation of cable slice. The water tree growth model was established to calculate the water tree density of cable, and the correlation between the macroscopic parameters of cable and the microscopic water tree density was analyzed. The results show that the longer the ageing time, the greater the carbon oxygen index and water content index, and the faster the rate of increase. Based on the correlation coefficient, a new mathematical model for predicting the growth density of water tree inside XLPE cable is established, which realize the combination of microstructure of water tree inside cable and macro test parameters.

The thermal conductivity mechanism and common thermal conductive fillers of thermal conductive silicone composites for electronic packaging were presented, the preparation strategies and research progress of filled-type high thermal conductive silicone composites were reviewed, and the future research direction of thermal conductive silicone composites for electronic packaging was prospected.

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.

In order to solve the problem that the current national standard can not fully meet the actual needs due to the imperfection and indeterminacy of the test method and judgment standard of partial discharge test of the electrical penetration assembly for reactor, on the basis of comprehensive consideration of various index requirements, we set a test scheme for partial discharge characteristics of electrical penetration assembly of medium voltage by pulse current method, and validation tests were carried out. The results show that it is reasonable to set the low value of partial discharge pulse parameter amplitude corresponding to the extinction voltage of the medium voltage electrical penetration as 15 pC, and partial discharge mainly occurs in the air gap between the multi-layer heat shrinkable tubes of its conductor components.

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 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 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.

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.