Review of Screening Sulfur Hexafluoride Alternative Gases Based on Density Functional Theory

Studies about environment-friendly SF6 alternatives have been paid more attentions recently. In this paper, the related researches on the method of sulfur hexafluoride substitutes based on density functional theory (DFT) are introduced. The screening methods for predicting the electric strength and liquefaction temperature of unknown insulating gas are described in detail, and the selected functional and basic set for calculation are analyzed. The influences of them on the calculation results indicate that the deviation between the calculated value and the experimental value is small at the M06-2X/6-311+G (3df) level. The influences of the microscopic parameters of the gas molecules selected during the prediction on the prediction results are compared. The analysis shows that the surface electrostatic potential is closely related to the liquefaction temperature and electric strength. The effects of halogen substitutions on the electric strength and liquefaction temperature of gas molecules and their changing rules are proposed. That is, as the relative molecular mass of halogens increases, the electric strength and liquefaction temperature also increase accordingly. In addition, the collision cross section of electron impact ionization is an important parameter for the study of insulation properties after screening. We compare the values of the collision section under the DM formula and the modified DM formula based on the density functional theory. The results show that the modified DM formula improves the accuracy of the calculation results. Finally, the direction of future research and development is pointed out, and a comprehensive evaluation system for SF6 alternative gas should be established under consideration of gas insulation, arc extinguishing, and environmental protection. © 2019, High Voltage Engineering Editorial Department of CEPRI. All right reserved.