Experiments on dynamic behaviors of small DC current vacuum arc

An arc voltage of a vacuum discharge is relatively low, but it establishes very rapidly just after the contact separation. Such a rapid increase of the voltage might cause some kinds of transient phenomena in a closed circuit. An oscillating current caused by these transient phenomena can create a current zero at the vacuum arc. If the amplitude of the oscillations is larger than the current there, the arc will be quenched. We have already reported these interruption phenomena with small DC current using a commercial circuit. Two kinds of current oscillation were observed. The first one is a forced oscillation type which was observed when step arc voltage was appeared, and we called this a transient phenomenon. The second one is a spontaneous oscillation type which was observed after a long arcing time, and we called this an instability phenomenon. The second one is sometime called a current chopping. In the present paper, in order to clarify these small current interruption phenomena, experimental results using a demountable vacuum chamber to investigate a movement of the arc at a current interruption will be demonstrated. The arc voltage and current were measured at the current quench, and we took photographs of arcs from two directions in every 1 ms. We calculate the conductance in the vicinity of current zero, and were examined by the parallel capacitor interrupting performance.