Rolling sphere – method or theory?

Abstract

The rolling sphere theory is based on two assumptions: (a) the point of strike of lightning is determined when the downward leader approaches the earth or a structure with a striking distance, and (b) lightning strikes the nearest earth object from the orientation point and so its worst position is the center of a sphere which attaches several earth objects. The conclusion: no lightning will strike the structure to be protected if its striking distance is greater than the radius of the sphere. While the efficiency of the air termination system is not determined by the radius of the sphere, the rolling sphere method is now the best design procedure for air termination systems. The paper summarizes the history and the physical background of the rolling sphere theory which was developed by Professor Horváth.