On the pulse shape of discharge currents

Abstract

Current pulse shapes of brush discharges from insulator surfaces and capacitive spark gap discharges were recorded on a fast oscilloscope and the data obtained fitted to assumed mathematical expressions by computer. The surface discharges were photographed using high sensitivity film, and their Lichtenberg figures made visible by a thin layer of Lycopodium. The geometry of a surface discharge depends on the radius of the discharging object. The number of foot-points of the discharge decreased with increasing radius; a sphere of 125 mm diameter caused one single foot-point, and a sphere of 25 mm diameter caused up to ten foot-points. The branching did not in any case occur at the surface of the electrode. The total current flow was concentrated to one single stem of at least five millimetres length. Resistances and linear energy densities of the surface discharges were calculated to be in the range of 1–4 kω and 3–40 μJ/mm respectively, whereas the capacitive discharges would have resistances of 1–90 ω and a linear energy density of 200–900 μJ/mm. The authors propose a new concept model for the discussion of the incendivity of electrostastic discharges.