In order to study the surface potential and electric field variation law of porcelain insulators under suspended sand and dust weather, a simulation model of xp-70 ceramic suspension insulator was established on the basis of electrostatic field model of finite element method, and the potential and electric field distribution law of porcelain insulators in various suspended sand and dust environments was summarized on the basis of finite element software calculation. The results show that the electrically neutral sand particles in the air can cause small distortion of the surface potential and electric field of porcelain insulator. When the sand and dust around the insulator are all positively charged, the surface potential will increase, and the surface electric field will decrease near the high voltage end and will increase near the low voltage end. When the sand and dust around the insulator are all negatively charged, the surface potential will decrease as a whole, the surface electric field will increase near the high voltage side of insulator string and will decrease near the low voltage side, and its distortion amplitude is proportional to the absolute value of dust particle size, concentration, and charge-mass ratio. When the insulator is in a mixed sand and dust environment of half charged and half electro-neutral, its surface potential and electric field will be distorted, and its distortion amplitude is less than that when the entire sand and dust are charged, and greater than that of the insulator alone in the sand and dust environment. When the insulator is in a "positive and negative" sand and dust environment, the distortion amplitude of surface potential and electric field is similar to the distortion amplitude in the electro-neutral sand and dust environment.

The thermal effect in the long-term operation of pumped storage generator sets will cause adverse effect on the main insulation performance of stator bars. Taking the VPI stator bar of an 18 kV pumped storage generator as the research object, we prepared samples and designed thermal ageing scheme. By means of dielectric property test, conductivity test, and breakdown characteristic test, the electrical properties of stator insulation under different ageing temperatures and different ageing cycles were explored. The test results show that there is obvious and complete loss peak in the bending section of stator bar. During the thermal ageing process, the dielectric constant frequency spectrum of insulating material shows an increasing trend with the increase of ageing period, and the dielectric constant of the bending section shows a stepwise decreasing trend with the increase of frequency. As thermal ageing progresses, the conductivity of samples increases gradually, and the absorption ratio and polarization index both show a decreasing trend. The breakdown strength of the straight section sample and the bending section sample continues to decrease, and the breakdown strength of the bending section sample decreases more significantly.

Infrared temperature rise detection is an effective means to screen faulty composite insulators. However, the causes of abnormal heating of composite insulators are diverse, and not all causes will evolve into malignant faults. Therefore, it is particularly important to distinguish the abnormal heating caused by different causes for the safe, stable, and economic operation of power grid. In this paper, the physical and chemical properties of two 220 kV retreated composite insulators with different heating characteristics were studied by SEM and FTIR, and their dielectric properties were also studied. The results show that the causes of different abnormal temperature rise are different. For the composite insulator whose heating part is concentrated at the end of high-voltage end and temperature rise is lower than 5℃, the epoxy resin of the core rod at the heating part has no obvious degradation, and the dielectric constant and dielectric loss factor have no obvious increase, while the sheath has holes and shallow microcracks, and the dielectric constant and dielectric loss factor increase with the increase of humidity. For the composite insulator whose heating part extends to multiple umbrella skirts and temperature rise is up to 40 ℃, the epoxy resin of the core rod has obvious degradation, and the dielectric constant and dielectric loss factor are 3.67 times and 79.4 times bigger than those of the normal part, respectively.

Epoxy composite is easy to accumulate space charge under high temperature and high electirc field condition, which would lead to local electirc field distort, and in severe case, partial discharge would produce and insulation would break down. Nano-MgO/EP composites with different doping rate were prepared by mixing nano-MgO particles into epoxy resin. Their glass transition temperature was measured by differential scanning calorimetry (DSC). Their trap characteristics were calculated by thermal stimulation depolarization current method (TSDC). Their space charge characteristics were measured by pulse electroacoustic (PEA) method. The results show that the addition of nano-MgO particles can increase the glass transition temperature of epoxy resin and inhibit the space charge accumulation in epoxy resin. With the increase of nano-MgO doping rate, the glass transition temperature of epoxy composite increases at first and then decreases, the deep trap energy level and density of nano-MgO/EP composite increase at first and then decrease, the space charge density of nano-MgO/EP composite decreases at first and then increases, and the electric field distortion trend is similar with that of space charge. When the doping rate of nano-MgO is 3%, the glass transition temperature of the nano-MgO/epoxy composite reaches the maximum value, and the ability to inhibit the space charge accumulation and electric field distortion is the best.

The distribution transformers serving in the distribution network of urban villages have been in heavy overload operation for a long time, and the number of transformers approaching or even exceeding their design life is increasing. Prolonging their service life by replacing natural ester insulating oil is a feasible method of life extension. In this paper, the thermal ageing characteristic of aged mineral insulating oil-impregnated paper in natural ester was tested to analyze the pyrolysis characteristics of cellulose. Then the residual life of oil-impregnated paper after replacing natural ester was predicted by the pyrolysis kinetic model of oil-impregnated paper cellulose. The results show that the influence of the residual mineral insulating oil in the oil-impregnated paper on the pyrolysis process of cellulose after replacing the natural ester can be ignored. The moisture content of insulating paper is an important factor affecting its pyrolysis reaction, and the replacement of natural ester can significantly decrease the moisture content of insulating paper and delay the pyrolysis rate of insulating paper cellulose.

Polymer film capacitors are widely used in many fields, such as high-pulse power technology, aerospace technology, and new energy vehicles due to their ultra-high charge and discharge efficiency. Polymer dielectrics used in energy storage applications often require high energy density and energy storage efficiency, and biaxial tensile polypropylene (BOPP) films, which are widely used in commercial thin-film capacitors, cannot meet the increasing demand for energy storage. Among many polymer dielectric materials, polymethyl methacrylate (PMMA) has attracted extensive attention due to its high breakdown strength, low dielectric loss, and easy processing. In this paper, the research progress of PMMA basic characteristic and composite dielectric materials in the field of energy storage was reviewed. The methods to improve the energy density and energy storage efficiency of polymer dielectric materials through chemical modification and physical modification were summarized, and the future development direction of dielectric materials was prospected.

A base gel was prepared with bisphenol A epoxy resin E124 as the main resin, polymercaptan as the curing agent, and imidazole as the accelerator. A single component high thermal conductive structural adhesive was prepared by adding different proportions and sizes of spherical alumina and irregular alumina into the base gel. The effects of different filling content and different particle sizes of alumina on the thermal conductivity, bonding strength, viscosity, and thixotropy of the single component high thermal conductive structural adhesive were studied. The results show that when the mass ratio of base gel to the three different particle sizes of alumina is m(base gel)∶m(40 μm Al₂O₃)∶m(2 μm Al₂O₃)∶m(0.5 μm Al₂O₃) =15∶59.5∶25.5∶6, m(base gel)∶m(40 μm Al₂O₃)∶m(5 μm Al₂O₃)∶m(0.5 μm Al₂O₃) =15∶59.5∶25.5∶8, m(base gel)∶m(40 μm Al₂O₃)∶m(10 μm Al₂O₃)∶m(0.5 μm Al₂O₃)=15∶68∶17∶8, three kinds of high thermal conductive structural adhesives cured at 90℃ for 15 min can be obtained, their thermal conductivity is 2.73, 3.05, 2.85 W/(m·K), their bonding strength is 5.49, 5.55 and 5.31 MPa, and their viscosity is 145 000, 127 467 and 118467 mPa·s, respectively. The volume resistivity of the three kinds of high thermal conductive structural adhesives is above 10¹⁴ Ω·m, and the adhesive survival rate after high temperature and humidity, cold and thermal shock is more than 70% and 90%, respectively. The performance of the high thermal conductive structural adhesive meets the basic performance requirements of screen printing and heat dissipation materials for chip packaging.

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 research on the correlation between the insulation strength and microscopic parameter of gas medium is beneficial to improve the development efficiency of SF₆ alternative gas. In this paper, based on density functional theory, the M06-2X functional and def2 series basis sets were used to establish the stable structures of 73 kinds of gas molecules. The Fukui function parameters that characterize the electron probability density difference were calculated, its correlation with insulation strength was analyzed, and the corresponding prediction model was established. The results show that the electrophilic index, local reduced electrophilic index minimum, local reduced nucleophilic index minimum, molecular volume, local surface electrophilic index maximum, local surface nucleophilic minimum have strong correlation with insulation strength. When the electron probability density in the prediction model is 0.000 05 a.u., the maximum determination coefficient is 0.812, and the mean square error is 0.094.