Initial stage of breakdown of a point-plane gap filled with high-pressure nitrogen and SF6

Abstract

The initial stage of breakdown of sulfur hexafluoride (SF6) and nitrogen in a nonuniform electric field at high pressures is studied. High voltage pulses with amplitudes of up to 350 kV have been applied across the discharge gap with the “point-plane” geometry of the electrodes. Experimental results on the dynamics of light emission from different zones of the discharge gap can be explained by generation of an ionization wave, which started from a potential electrode with a small radius of curvature. It is found that the speed of the ionization wave front in nitrogen and SF6 is higher in the second half of the discharge gap as compared to the first one. It is shown that the speed of ionization wave front decreases as SF6 and nitrogen pressure increases. The average speed of ionization wave front is shown to be ∼2 cm/ns in SF6 under a pressure of 0.25 MPa and ∼3.6 cm/ns in nitrogen under a pressure of 0.3 MPa under the negative polarity of high-voltage pulses when bridging a discharge gap of about 13 mm.