A novel film capacitor was prepared by using a mass-produced surface modified high dielectric polypropylene film, and the power density, energy storage properties, capacity retention ratio, and the cycle life under large current of the capacitors were studied. The results show that the maximum energy storage density of the new capacitors with the surface modification polypropylene film can reach to 3.2 J/cm³, and the capacitor shows excellent comprehensive performances.

Three kinds of soluble polyimide (PI) resins were prepared from 4,4′-hexafluoroisopropylidene)bisphthalic anhydride (6FDA) and three kinds of romatic diamine monomer containing rigid-rod amide bonds in the molecular chains by one-step high temperature solution polycondensation reaction, respectively. And then three kinds of transparent PI films were prepared by the N,N-dimethylacetamide (DMAc) solution of the above resins. The films were tested by attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, dynamic mechanical analysis, thermomechanical analysis, and UV-visible spectrum, and their yellowness index was tested. The results show that the PI films exhibit good optical transparency, their ultraviolet cutoff wavelength is below 380 nm and the optical transmittance is over 80% at the wavelength of 500 nm. In addition, the PI films exhibit good thermal stability with the glass transition temperatures (T_g) higher than 320℃ and the 5% weight loss temperatures (T_5%) over 520℃. The linear thermal expansion coefficients (CTE) of the PI films are all lower than 50×10^-6/K, indicating that the introducing of rigid amide bonds can efficiently enhance the high-temperature dimensional stability of the solution-processable fluoro-containing PI films.

The effect of different contents of bis-triethoxysilylpropyl tetrasulfide (Si69) and bis(tert-butylperoxy diisopropyl) benzene (BIBP) on vulcanization characteristics, mechanical properties, and electrical insulation property of EPDM were compared and analyzed. The results show that with the increase of Si69 and BIBP content, the curing speed increases, the process positive curing time decreases, the maximum torque increases, the crosslinking density of the rubber increases and the mechanical properties are improved. With the increase of Si69 content, the electrical insulation property of the rubber decreases; with the increase of BIBP content, the electrical insulation property of the rubber increases gradually.

In this paper, three metal-organic framework (MOF) materials MOF-505, Cu-BTC, and MIL-100(Fe) were prepared by solvothermal method, and Cu-BTC with the highest adsorption capacity was selected. The equilibrium adsorption capacity of Cu-BTC, activated carbon, 13X molecular sieve, and activated clay at different initial concentrations and adsorption temperatures was systematically studied. The difference among the adsorption characteristics for aminophenazone of the MOFs was explained by simulation calculations using simulation software. The results show that the adsorption capacity for aminophenazone of Cu-BTC is much higher than that of the other three adsorbents. Under different temperature, the equilibrium adsorption capacity of BTC for aminophenazone at different initial concentrations has much difference, thus the appropriate adsorption temperature should be selected to achieve the optimal adsorption capacity.

Crosslinked polyethylene/organic montmorillonite (XLPE/OMMT) nanocomposites were prepared by melting blending method. The performance of samples before and after thermal ageing were characterized by small angle X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and mechanical properties test. The results show that with the mass fraction of 0.5%, OMMT can be well dispersed in the matrix before ageing. However, OMMT agglomerates when the filler doping amount increases. There are only a few chemical bonds between OMMT and XLPE matrix, they mainly coexist in the form of physical entanglement. The crystallinity of nanocomposites decreases due to the space steric effect of OMMT lamella. After ageing, the layer spacing of XLPE/OMMT-0.5% samples decreases and the crystallinity increases. With the increase of OMMT doping amount, the interlayer spacing of OMMT increases due to the breakdown of XLPE molecular chain and the thermal rearrangement of OMMT in matrix. Due to thermal ageing, the completeness of crystal structure of nanocomposites gets worse, the crystal size distribution becomes wider, and the crystallinity decreases significantly. The molecular chain structure of nanocomposites is seriously damaged by thermal oxidation and thermal cracking. The mechanical property of XLPE/OMMT-0.5% decreases slightly after ageing, and when the content of OMMT exceeds 0.5%, the mechanical properties of nanocomposites decrease seriously. And the samples become brittle and hard.

Three typical imported PP resins with a large market share for capacitor application were chosen, and their molecule structure, aggregation structure, and electrical properties were systematically measured. The influence law of molecular weight and distribution on the crystallization properties, as well as the action mechanism of crystallization properties on dielectric and breakdown properties was investigated, and in consequence the correlations between microstructure and macroscopic electrical properties was built. The results show that optimizing the molecular weight and distribution avoiding too large and narrow can contribute to regular and compact alinement and stacking of molecules, and then the orientation of dipole and transportation of electrons can be inhibited, resulting in the decrease of dielectric loss and increase of breakdown strength.

Metal particles in gas insulated metal enclosed switchgear (GIS) and gas insulated enclosed transmission line (GIL) can bounce near the insulator under the electric field, which intensifies the charge accumulation and may cause surface flashover in serious cases. In this paper, a 126 kV real size disc insulator was selected as the test sample. A sealed chamber and coaxial structure electrodes were designed, and the effects of bouncing metal particles on the surface charge accumulation behaviors of insulator at different temperatures (23, 40 and 60℃) were studied by using Kelvin electrostatic probe. The results show that the charge accumulation on the nonplanar region is closely related to the motion mode of metal particles at room temperature. And the charge accumulation on the insulator surface is positively correlated with the temperature. As the temperature rise to 60℃, the metal particles moving to the vertical surface of the ground electrode are easy to cause surface flashover, and a large number of heteropolar charges would be accumulated on the non-plane region in the same radial direction as the flashover.

In order to study the effects of different damping paths on cables, we set up a variety of endogenous and exogenous damping paths according to operating experience. Accelerated damping test were conducted on cables for 90 cycles, and the insulation resistance, partial discharge, and depolarization current were measured regularly. Then the moisture state of the cable was comprehensively evaluated by TOPSIS method. The results show that during cable operation, moisture can enter and rapidly spread inside the cable through the broken body, cable joints, and various interface structures of the cable terminals. The degradation effects of moisture through cable joints and endogenous moisture on the insulation is the most prominent, which should be prevented and taken seriously. Furthermore, the comprehensive evaluation of electrical properties based on insulation resistance, partial discharge, and depolarization current can effectively explore the damping process and identify the moisture state, which can be applied to practical engineering to evaluate the damp problem of distribution network cables in warm-damp environment.

The simulation model of 35 kV prefabricated cable terminal was established to simulate and calculate the electric stress, thermal stress, and mechanical stress distribution of the cable terminal under the impulse voltage. The electric field, temperature, and stress of body insulation, semi-conductive layer, and shielding layer were calculated and analyzed, and the influence of harmonic wave with different frequency on the electric field distribution was considered. The results show that the influence of high frequency signal on permittivity does not lead to large distortion of electric field intensity, and the change of electric field intensity is not obvious. At the same time, the temperature rise of cable terminal caused by impulse voltage is small, and its influence can be ignored. The impulse voltage increases the mechanical stress at the intersection of the semi-conductive layer and the stress cone, and the maximum radial strain reaches to 2.54%, which makes the position of the semi-conductive layer prone to produce air gap and is the main cause of cable terminal damage. It is concluded that not only the electric field optimization but also the elastic strain of the material should be considered in the material selection and structural design.

A thermal-mechanical simulation model of cable insulation fused joints was established, and then the effect of the difference in fluid temperature and flow rate between water-cooled and air-cooled cooling methods on the internal stress distribution of fused joints was analyzed. The effect of the material performance difference between the new cross-linked polyethylene and the old cross-linked polyethylene on the stress distribution was also studied. The results show that the change of water-cooling parameters has a great influence on the stress of the insulation layer of the fusion joint, and the stress distribution is concentrated near the interface of the new and old insulation layer, and the difference of the material properties leads to the similar stress distribution.

The relationship between the withstand voltage and the thickness of the sheath was studied when the air gap distance is 0, 5, 10, 15 cm, respectively. The influence of the length of sheath on the development of creeping discharge was studied when the sheath surface is dry, wet, and dirty, respectively. The results show that with the increase of the length and thickness of gap, the breakdown voltage of the insulating sheath-air combined gap increases nonlinearly, and the increase rate of the breakdown voltage also increases. The surface flashover electric field intensity of the insulating sheath decreases obviously in dirty state, the average flashover electric field intensity is 1.2 kV. Based on the above research, the configuration of anti bird droppings flashover insulating sheath was obtained. The thickness of the sheath is determined according to the line voltage level, and then the covering length is determined by the maximum surface flashover distance. It is recommended that the thickness and covering length of sheath in 110 kV transmission line is 6 mm and 60 cm, respectively; while the thickness and covering length of sheath in 220 kV transmission line is 8 mm and 110 cm, respectively.

The accumulation test of metal particles in oil between spherical electrodes under different ratios of AC/DC composite voltage was carried out, the partial discharge (PD) signals at different moments were collected simultaneously. And then the discharge frequency and average discharge quantity were counted, and the correlation between the aggregation behavior of metal particles and PD characteristics was analyzed. The results show that the accumulation area of metal particles under DC voltage is the largest, and the metal particles aggregated the most closely under 3:1 AC/DC composite voltage. The discharge frequency decreases with time, while gradually increases with the increase of AC component in AC/DC composite voltage. It is considered that the collision frequency between metal particles and electrodes and the closeness of particle accumulation are the main factors affecting the frequency of partial discharge and the average discharge quantity.

According to isotope tracing technology, we used stable isotope tracer ¹⁸O₂ to carry out SF₆ partial over-thermal decomposition experiments to simulate the decomposition of SF₆ under sustained high temperature. The influence mechanism of trace O₂ on the overheating decomposition of SF₆ was analyzed by obtaining the changes in the volume fractions of the main oxygen-containing products labeled by ¹⁸O. The results show that under overheating conditions, trace O₂ preferentially reacts with SF₃, SF₂, and SF to generate SOF₃, SOF₂, and SOF, followed by generating a small amount of SO₂F₂. It is said that O₂ is the main source of oxygen for the formation of SOF₂. Besides, under overheating conditions, SF₆ can be completely decomposed to generate elemental S, which reacts with trace O₂ to generate SO₂.

The broadband dielectric response of oil-paper insulation was studied, and broadband dielectric response tests were carried out on laboratory samples of oil-paper insulation with different moisture contents. According to the relaxation polarization part of dielectric spectrum, the spectral parameters characterizing the moisture degree were extracted, and their relationship with the moisture content in the oil-paper insulation was analyzed. Further moisture tests for the oil-immersed bushing scaled-down model were designed, and the application of the spectral parameters in the moisture diagnosis of bushing was discussed. The results show that the low-frequency polarization process in the relaxation polarization spectrum is more sensitive to the moisture content, and its loss peak value can be used as a characteristic parameter to characterize the moisture content; under different moisture types of the bushing, the change patterns of the loss peaks and characteristic frequencies of the low-frequency and high-frequency relaxation polarization are different, which can be used as a preliminary criterion for the moisture type of the bushing.

The typical defects model of heat-shrinkable and cold-shrinkable cable accessories were established, and partial discharge tests were carried out at 0.1 Hz ultra-low frequency and oscillatory wave voltage. The differences in the partial discharge inception voltage (PDIV), the PD quantity, the number of PD and other parameters of the typical defects under the two voltages were measured and compared, and the formation mechanism of these differences was analyzed. The results show that for most of the measured defects, compared with under 0.1 Hz ultra-low frequency voltage, the PDIV under the oscillating wave voltage is lower, the PD quantity is larger, and the number of partial discharge pulses is more. The difference in the voltage distribution mechanism and the voltage recovery rate at the defect location is the main reason for the above-mentioned difference.

According to the sand parameters around the transmission line corridors in Tibet, Xinjiang, Qinghai and other high incidence of sandstorms regions and the relevant data of dust weather, the wind speed, particle size, concentration, charge/mass ratio and other specific parameters for sand simulation were determined, and a testing apparatus was built. The effect of simulated sand conditions on the power frequency discharge voltage of external insulation in the gap was tested by using this device at an altitude of 2 200 m. The results show that the simulated sand dust environment will decrease the power frequency discharge voltage of the short gap below 0.2 m, but will not reduce the power frequency discharge voltage of the long air gap above 0.2 m, and the charged dust in the air itself is not the cause of the gap trip discharge.

According to the characteristics of series resonance circuit, a new model for calculating the dielectric dissipation factor of high-voltage power cable was established, and a new dielectric loss factor calculating formula derived from the differential power of the series resonance circuit was proposed. On the basis of test model, the dielectric dissipation factor of XLPE power cable was calculated by the step-up or step-down process of the series resonance to solve the problem of dielectric dissipation measuring of high voltage and large capacity cable. The results show that the simulation calculating values of circuit parameters and field test results match with the actual values. Compared with conventional electric bridge method, the test method for calculating dielectric dissipation factor based on the resonance characteristic is more accurate to a certain extent. This provides a reference for testing the dielectric dissipation factor of high voltage and high capacity power cable.