The Relation Between Stroke Current and the Velocity or the Return Stroke

The velocity of the return stroke is an important element in estimating (1) the surge impedance of the return stroke, (2) the potential of the downward leader, and (3) the length of the last striking distance. The energy required to establish an arc plasma can be determined from laboratory tests. By equating this quantity to the energy required to retard the velocity of a traveliing wave, the consequent velocity of the return stroke can be evaluated in terms of the stroke current.