V-I Characteristics of Short Gap Arc in Air at C, Ag, Cu, Pd, and W Electrodes--Measurement and Formulation for Practical Use--

Abstract

Short gap arc V-1 characteristics are essential to discussions on behavior of contact arc at opening and closing. From this point of view, some conventional arc V-I characteristics were reviewed and inconvenient points of them for practical use were pointed out: (I) not a few electrode-material-dependent constants needed in the equation of V-I relation, (2) difficulty in the prediction of real arc extinction phenomena. In order to overcome these inconveniences, the author measured short gap arc V-I characteristics originally, and tried to formulate them into a simple form on the assumption that the arc column V-I characteristics are little dependent on electrode materials but the unstable arc region is strongly dependent on electrode materials. Measured arc column voltage was directly proportional to the square root of gap length and inversely proportional to the cube root of arc current. Arc became unstable when arc current decreased near to the value generally known as the minimum arc current. It was not necessarily the case that the arc extinguished completely at the minimum arc current, but, depending on the circuit conditions, the arc often existed discontinuously below the so-called minimum arc current. Simple empirical V-1 characteristics were proposed for practical use, together with the unstable arc region as the information for arc extinction phenomena.