Analytical investigation of electrical breakdown properties in a nitrogen- SF_6 mixture gas

摘要

The electrical breakdown properties in nitrogen gas mixed with SF _6 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 SF_6 gas are obtained in terms of the electron temperature T_e by assuming a Maxwellian distribution of the electron energy. The attachment coefficient of SF_6 gas is also obtained in terms of the gas temperature T_e. An algebraic equation is obtained, relating explicitly the electron breakdown temperature T_b in terms of the SF_6 mole fraction. It was found from this equation that the breakdown temperature T_b increases from approximately 2 to 5.3 eV as the mole fraction increases from zero to unity. The breakdown temperature T_b of the electrons increases very rapidly from a small value and then approaches 5.3 eV slowly as the SF_6 mole fraction increases from zero to unity. This indicates that even a small mole fraction of SF_6 in the gas dominates the electron behavior in the breakdown system. The breakdown electric field E_b derived is almost linearly proportional to the breakdown electron temperature T_b. The experimental data agree remarkably well with the theoretical results. Therefore, it is concluded that even a small fraction of SF_6 gas dominates nitrogen in determining the breakdown field. In this context, nearly 25% of the SF_6 mole fraction provides a reasonable enhancement of the breakdown field for practical applications.