Calculation of interception efficiencies for air-terminations using a dynamic electro-geometrical model

The paper firstly presents the method of a dynamic electro-geometrical model. In contrast to the classic rolling-sphere it does not use fixed radii, it works with a varying radius. The method only uses existing and in international standards accepted results, fundamentals of lightning physics, and investigations; on that base a numerical method is elaborated. Using the dynamic electro-geometrical model, secondly some examples of protection with air-termination rods planned with the classic rolling-sphere according to IEC 62305-3 and for the classes of protection I-II-III-IV are investigated. It is shown, that the interception efficiencies are much higher than documented in the standard series IEC 62305. Reason is, that the method of the rolling-sphere is conservative, and that it gives the planner of lightning protection systems only the points, where lightning may strike, but without a rating with a striking probability. On the other hand this result clearly indicates, that using the classic rolling sphere method one is always on the “safe side”.