Time Constants of Flat Arcs Cooled by Thermal Conduction

Time constants of flat arc bands, burning between nonevaporating plates, were theoretically and experimentally investigated. Neglecting the convection term, the relevant energy balance equation was solved in a one-dimensional approximation. Expressions for the distribution of electrical gradient were inversely proportional to the plate distance and were dependent, as well, on the heat-flux potential. The arc time-constant was proportional to the square of the plate distance and inversely proportional to the thermal diffusivity. Measurements at current zero of alternating-current arcs, operating at 2000 c/s and 1000 amperes, confirmed the strong dependency of the arc time-constant on the plate distance. Time constants as small as 0.1 μs were obtained.