Behaviour of grounding systems excited by high impulse currents: the model and its validation

The behaviour of grounding systems excited by high impulse currents (such as lightning strokes or phase to ground faults) considerably differs from that at low-frequency and at low-current: inductive behaviour can become more and more important with respect to resistive behaviour and, in addition, these currents can generate soil breakdown (which makes the impulse response typically nonlinear). Many experimental tests confirm these aspects. In order to obtain a correct design of electrical systems, with respect to the protection of installations against anomalous events, it is fundamental to predict the impulse characteristics of grounding systems. An efficient solution to this problem may be obtained by a mathematical model based on a circuit approach. The development of this model (which is able to simulate complex grounding systems when nonlinear ionization phenomena take place) is described in this paper. The model has been validated by comparing the numerical results both with experimental tests and with the simulations executed by various approaches.