Low current arc modes of short length and time: a review

Until the middle of the 20th century the electric arc was known solely as a steady, self sustaining gas discharge phenomenon requiring certain minimum values of current and voltage, depending on the electrode material and the gas environment. Special investigations on material transfer in contacts switching low direct currents, however, revealed step by step that there were certain till then unknown unstable arc modes appearing in extremely short electrode gaps only but requiring minimum current and voltage values distinctly lower than those of the classical steady arc discharge in air. Low current break arcs have to pass one or more of these transient modes whether or not they may eventually attain the steady gas arc mode.