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.

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 order to improve the insulation ability of the three media interaction area of basin insulator, the reasons of the accumulation of foreign body, and the flashover along the basin insulator surface induced by the structure design defect of the three media interaction area was analyzed from the composition of three media interaction area, the movement characteristics of foreign body and the typical discharge phenomenon. Through electric field simulation, the influence of grounding shielding electrode, the flange thickness of basin insulator, and the distance between the grounding shielding electrode and the busbar cylinder flange on the electric field intensity in the low potential three interaction area were studied, the variation law of electric field in the high potential three interaction area with tilting angle and three media interaction area width of basin insulator were given. The calculation method of the thickness of the high voltage side of grounding shield electrode to prevent resin through failure and the criterion of electric field check in the three media interaction area were presented. The results show that the reasonable structure design of three media interaction area with high and low potential can effectively inhibit the surface flashover induced by foreign matter accumulation.

In this paper, the modification methods of polypropylene, the development and operation of polypropylene cables, and the existing regulations and specifications of polypropylene cables were reviewed. According to the research and development status of polypropylene cables, the problems that may be encountered in the future operation of polypropylene cables were summarized and research suggestions were put forward, which can provide reference for the subsequent research and commercial application of polypropylene cable.

Epoxy resin impregnated crepe paper (ERICP) insulating materials are widely used in power equipment insulation, and moisture is an important reason affecting their insulation state. In this paper, the frequency domain spectroscopy (FDS) technology was used for insulation condition evaluation. Firstly, ERICP samples with different moisture content were prepared and carried out FDS tests. Then, according to the FDS spectrum curves, the variation law of FDS characteristic parameters with moisture content was analyzed. Finally, the dielectric modulus spectrum and modulus factor were introduced, and the insulation condition evaluation method of ERICP was proposed. The results show that the change of moisture content affects the overall change law of FDS curves. The dielectric modulus can effectively suppress the influence of DC conductivity to characterize the internal relaxation process. The dielectric modulus spectrum of ERICP samples has obvious relaxation peak in the low-frequency range, and the characteristic frequency of relaxation peak increases with the increase of moisture content. The integral area of the imaginary part of dielectric modulus can be used as a characteristic parameter to characterize the insulation condition of ERICP. The relationship between the modulus factor and moisture content has 0.997 5 of goodness of fit with the exponential function.

In view of the degradation of insulating properties of ethylene propylene diene monomer (EPDM) cables caused by mechanical, electrical, and thermal stresses during operation, the dielectric spectrum of EPDM used for power cable insulation in tensile state was studied. Firstly, a tensile force applying fixture was designed, and a multi-stress dielectric spectrum testing system was built. The dielectric spectrum of EPDM under the joint action of tensile force and thermal stress was measured. The influence of tensile ratio on the dielectric loss factor of EPDM was analyzed emphatically. Then, the characteristic parameters of dielectric spectrum and their variation with tensile ratio were obtained by Cole-Cole model. The change of chemical groups of EPDM was analyzed by Fourier transform infrared spectroscopy (FTIR) from the microscopic view. Finally, the properties change mechanism of EPDM after tensile was summarized combining with carrier apparent mobility. The results show that the tensile ratio has significant influence on the complex dielectric constant and dielectric loss factor of EPDM, especially when the frequency is low, the dielectric loss factor decreases at first and then increases with the increase of tensile ratio. The analysis based on Cole-Cole model shows that the DC conductivity, relaxation strength, and relaxation peak frequency of EPDM decrease at first and then increase with the increase of tensile ratio. Combining with Fourier infrared spectroscopy, it is concluded that the EPDM molecular chain will break when the tensile ratio reaches a certain value, and the carrier mobility extracted from the depolarization current decreases at first and then increases with the increase of tensile ratio.

As a kind of environment friendly liquid dielectric with high ignition point and degradability, natural ester insulating oil is widely considered as a good substitute of mineral oil in power transformers. In order to improve the electrical and thermal ageing properties of natural ester-paper insulation system, the surface of cellulose insulation paper was modified by silane coupling agent, and the oil-paper composite insulation combinations of natural ester, traditional mineral oil, ordinary insulation paper, and silane modified insulation paper were conducted accelerated thermal ageing tests. The ageing characteristic paremeters of oil-paper during the thermal ageing of four combinations were compared and analyzed. The results show that the insulating paper modified by silane can maintain a relatively complete three-dimensional network structure of cellulose during thermal ageing, and improve the ageing resistance and electrical performance of the natural ester-paper system.

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.

On the basis of the crystal structure of piezoelectric effect of polyvinylidene fluoride (PVDF) polymer, the effects of different annealing temperatures (60-160℃) on the surface crystal morphology, crystal size, crystallinity, and key dielectric parameters including polarization response curve and piezoelectric coefficient of PVDF film samples were studied. The results show that the sample crystal size and crystallinity increase with the increase of annealing temperature in the range of 60-140℃. The polarization curves show higher residual polarization intensity and hysteresis, and the piezoelectric coefficient increases from 11 pC/N to 27 pC/N with the increase of annealing temperature. When the annealing temperature reaches 160℃, cracks appear on the surface of sample, and consequently the breakdown is easy to occur in the polarization process, and the dispersity of piezoelectric coefficient is large.

In view of the high concentration of industrial dust pollution in some areas of Ningxia at present, considering the actual situation of uneven roughness of insulator surface in Ningxia power grid, the pollution particle deposition model of insulator surface under high pollution coverage was obtained based on the principle of energy conservation. The multiple physical field coupling insulator natural pollution simulation model was built by using COMSOL simulation software. Taking porcelain insulators of 110 kV AC transmission line near an industrial park in Wuzhong, Ningxia as the research object, the coupling effects of wind speed, particle size, pollution composition, and voltage type on the natural contamination characteristics of insulator surface were simulated. The results show that the pollution adhesion rate in the AC field shows irregular "M" shape along the shed, and the adhesion rate of silica is the highest. In the DC field, the pollution adhesion rate shows "U" shape along the shed, and the adhesion rate of iron oxide is the highest. Compared with the simulation model of insulator contamination on uniform rough surface, the model proposed in this paper can effectively improve the accuracy of simulation results and better reflect the contamination distribution of each shed of insulator string in the high-pollution industrial dust environment.