Dynamic Measurements of the Current Distribution in the Foot of an ARC Propagating Along the Surface of an Electrotype

Measurements of the arc current distribution obtained for pertinent flashover conditions are reported. A new experimental technique for measuring the distribution of the current in the foot of the arc as it progresses at the surface of an electrolyte is described. Results indicate a sharp current density gradient at the forward edge of the arc foot and a low gradient in a region extending a few centimeters behind. These results are compatible with conformal mapping of the current streamlines, provided that account be taken of a current in the electrolyte which flows parallel to the arc current. This parallel current was measured, in the electrolyte throughout the entire length of the arc during flashover. A propagation model is also proposed which stresses the importance of this asymmetrical shape of the current distribution in the continuous regeneration of the arc channel in the forward direction. An average current density of ~2 A/cm2 was measured, although a peak current density of ~30A/cm2 was measured in the arc core. These results and the formulation of the proposed model are compared with those reported in the literature.