Analytical investigation of electrical breakdown properties in a nitrogen-SF6 mixture gas

Abstract

The electrical breakdown properties in nitrogen gas mixed with SF6 are analytically investigated in this article by making use of the ionization and attachment coefficients of the mixed gas. The ionization coefficients of nitrogen and SF6 gas are obtained in terms of the electron temperature Te by assuming a Maxwellian distribution of the electron energy. The attachment coefficient of SF6 gas is also obtained in terms of the gas temperature Te. An algebraic equation is obtained, relating explicitly the electron breakdown temperature Tb in terms of the SF6 mole fraction χ. It was found from this equation that the breakdown temperature Tb increases from approximately 2 to 5.3 eV as the mole fraction χ increases from zero to unity. The breakdown temperature Tb of the electrons increases very rapidly from a small value and then approaches 5.3 eV slowly as the SF6 mole fraction increases from zero to unity. This indicates that even a small mole fraction of SF6 in the gas dominates the electron behavior in the breakdown system. The breakdown electric field Eb derived is almost linearly proportional to the breakdown electron temperature Tb. The experimental data agree remarkably well with the theoretical results. Therefore, it is concluded that even a small fraction of SF6 gas dominates nitrogen in determining the breakdown field. In this context, nearly 25% of the SF6 mole fraction provides a reasonable enhancement of the breakdown field for practical applications.