Electrical Breakdown of Air at High Voltages

Abstract

PREVIOUS measurements^1–3 in this Department of pre-breakdown ionization currents in uniform electric fields in air have shown that, using gap voltages up to about 80 kV, and values of pd_s∼2,300 mm mercury cm (p the gas pressure; d_s the sparking distance), the steady-state spatial growth of ionization is a consequence of the operation of primary and secondary ionization processes together with processes of electron attachment. Further, the value of the static breakdown potential, V_S, calculated from the Townsend criterion and using the values of apparent primary and secondary ionization coefficients determined from observed pre-breakdown Steady-state measurements, was found to be equal to the measured sparking potential, within the experimental error, over this range of high gap voltage. It was concluded, therefore, that the mechanism determining the criterion was based on the action of the primary and secondary processes. The upper limit of the range investigated in this previous work was set by the voltage output of the high-voltage generator, for work with which the ionization chamber used was designed.