Analysis of the Insulation Characteristics of C3F8 Gas Mixtures with N2 and CO2 using Boltzmann Equation Method

This paper studied the insulation characteristics of C3F8 gas mixtures with N-2 and CO2 from the point view of electron swarm parameters. The density-normalized effective ionization coefficient (alpha-eta)/N and electron drift velocity V-e in binary C3F8-N-2 and C3F8-CO2 gas mixtures are calculated by solving the Boltzmann equation in the condition of steady-state Townsend discharge experiment. Values of the limiting electric field strength for which the electron ionization exactly balances the attachment are derived from the effective ionization coefficient data. It is found that the limiting field strength of C3F8-N-2 gas mixture is greater than that of C3F8-CO2 for C3F8 gas content k varied from 0% to 100%, and the C3F8-N-2 gas mixture containing 20% proportion C3F8 can achieve 60% dielectric strength of pure C3F8. Additionally, the synergistic effects of the insulation strength for C3F8 gas mixtures are also evaluated and compared with that of SF6-N-2 mixture. The calculation results, together with the discussions on liquefaction temperature and global warming potential indicate that gas mixtures containing C3F8 are feasible for applying in electric power apparatus as insulation medium.