Prebreakdown phenomenon in SF6-N2-mixtures at various pressures

Investigations were carried out to establish the dielectric behaviour of SF₆, N₂ and their mixtures. Prebreakdown currents were determined using plane/ plane, rod/plane and plane with protrusion/plane electrodes at constant gap length and various pressures at room temperature under direct voltages of negative polarity. No measurable prebreakdown currents were observed in the plane/plane configuration. In the presence of a small protrusion on the plane cathode, appreciable amounts of prebreakdown current were recorded. In the rod-plane gap prebreakdown currents were observed which depended on pressure, gas ratio and the applied voltage. In this case currents of pulsed nature were succeeded by steady currents and finally steady currents superimposed by pulses were observed with increasing voltages. Optical measurements showed good correlation between light emitted in the gap and different types of prebreakdown currents observed. The currents just before breakdown in SF₆-N₂ mixtures and in pure SF₆ do not differ appreciably from each other.