Experimental characterization of arc instabilities and their effect on current chopping in low-surge vacuum interrupters

In low-current vacuum arcs, short (<500-ns) peaks in arc voltage (instabilities), with a height of up to ten times the normal arc voltage, are abundantly present. The instabilities are thought to be caused by ion starvation near the anode. A number of parameters of these instabilities, occurring in vacuum interrupters with AgWC (low-surge) and CuCr (conventional) contact material, have been analyzed statistically in a practical AC circuit. A striking difference in median rate of rise and height is found. It is found plausible that these parameters reflect important switching characteristics such as recovery (peak rate of rise) and current chopping level (peak height). Also, the dependence of the parameters on momentary arc current and contact distance is studied and explained qualitatively