A new method for design of the air termination system of high voltage open air stations

High-voltage overhead substations can be protected against direct lightning strokes by vertical rods or by stretched horizontal conductors. But using the common principles of protected space, the interception efficiency cannot be estimated. In the first step, the Hungarian practice applies the rolling sphere method because it is independent of the forms and sizes of the protective devices. Further the rolling sphere method has been used with good experience for 35 years. The second step is an evaluation of the expected frequency of interception failure based on the principle of attractive space and the statistical distribution of the lightning current. The result is the probability of a direct stroke whose current exceeds a threshold and so the risk of a fall out can also be estimated.