Corona stabilization at negative impulse stress in SF6 and SF6-N2-mixtures

Measurements have been made to evaluate the characteristics of impulse corona at negative impulse stress. It is shown that for the parameters investigated the corona onset voltage is a linear function of the degree of homogeneity of the electrode arrangement for different pressures and mixture ratios. It is also shown that the corona onset voltage is a linear function of the pressure for different gap distances and mixture ratios for the parameters investigated. The breakdown voltage at impulse stress has been measured for a constant formative time lag, for different gap distances, for various degrees of homogeneity (η=E_mean/E_max was varied from 0.76 to 0.04), and for different SF₆-N₂ mixtures. Measurements of the breakdown voltage have shown that the corona stabilizing effect exists up to a mixture ratio of 10% SF₆ to N₂. It has been found that a slightly inhomogeneous electrode arrangement (η=0.26) has a lower dielectric strength than a strongly inhomogeneous electrode arrangement (η=0.04)