Influence of current frequency on the dynamic voltage/current characteristics of vacuum arcs

Measurements of arc voltage were carried out for sinusoidal current wave with frequency from 50 Hz to 6.0 kHz and peak currents up to 13 kA. The plain CuCr butt contacts at fixed gap lengths of 2 and 10 mm were used. The obtained characteristics enabled to state that: (a) the shape and value of the arc voltage during the half cycle sinusoidal current flow depend on the current amplitude and frequency as well as on electrode spacing; (b) the instantaneous current value of high-amplitude fluctuations (HAF) onset in arc voltage, increase with current amplitude and frequency increase; and (c) the arc voltage beyond the range of HAF occurrence is greater, at the same instantaneous value of the current, for higher current frequency; it is also greater during the current increase than its decrease. The qualitative correlations between the measured vacuum arc voltage and an expected discharge mode have been presented.