Calculation of the voltage on earth impedance caused by lightning impulse current

In case of lightning stroke into a tower the impulse current behaviour of the ground is of great importance. A simplified model for estimation the lightning performance of grounding electrodes has been evaluated. Based on field theory the inductive character of the earthing impedance is explained. With the help of computer calculations the role of influencing parameters is discussed as well. An approximate formula is derived which helps the practical computation of the maximal voltage peak.