Structure-Property Relationship To The Dielectric Strength And Molecular Design Method Of SF₆ Alternative Gas

It is urgent to find an applicable SF6 alternative gas for the high Global Warming Potential of the SF6.Now that the types of compounds are increasing,it is impractical to judge the dielectric strength of gas by test and test individually,and new gas molecules can not be obtained through discharge test.The molecular structure determines the properties,so we can start from the analysis of the influence of the gas molecular structure on the dielectric strength and establish a quantitative structure-property relationship model to determine the dielectric strength quickly and guide the selection or design of alternative gas molecules.In this paper,the molecular structure of insulating gas is optimized and calculated based on density functional theory.According to the gas discharge theory and molecular descriptor screening method,four molecular descriptors that have a significant impact on the dielectric strength are obtained:van der Waals volume,ellipsoid positive electrostatic surface area,lowest unoccupied orbital energy and highest occupied orbital energy value.For the four molecular descriptors screened out,the QSPR model between them and the dielectric strength was established using multiple linear regression and artificial neural network methods.The correlation coefficients R were 0.954 and 0.995,which can describe the molecular descriptors and the relationship well.Corresponding relationship of dielectric strength,and multiple linear regression combined with artificial neural network method can effectively improve the prediction accuracy of dielectric strength.Taking into account the influence of chemical bonds on the dielectric strength,for gas molecules containing unsaturated bonds,an improved QSPR model was established by using the MLR method.The results show that the electrostatic overall surface area and the balance of charges affect the dielectric strength.The key parameter of the model R is 0.988,indicating that the prediction accuracy of the QSPR model established for specific molecular structure has been further improved.In order to analyze the groups that affect the dielectric strength,then characterize and calculate the groups of gas molecules,put forward the characteristics of molecular topological index describing insulating gas,and calculate the atom-type E-state indices and Grouped E-state indices of insulating gas molecules.The stepwise multiple regression method is used to establish the relationship between the electrical topological index and the dielectric strength,then obtain the groups that have a significant impact on the dielectric strength:>CH-,=C=,-F,-C≡N,-Cl,and>C=O.Each group has a positive contribution to the dielectric strength,and can be prioritized when selecting groups to design SF6 alternative gases.Finally,the group substitution method is used to calculate and analyze the influence of the group substitution position on the dielectric strength,and the order of the symmetry group to high dielectric strength gas is calculated and analyzed.The results show that the high-order symmetric molecular configuration and the off-diagonal distribution of substituent groups can improve the dielectric strength.Summarizes the characteristic descriptors,characteristic groups and molecular spatial configuration that affect the dielectric strength,finally considers the influence of the gas boiling point,and proposes molecular design method of SF6 alternative gases.