Impulsive currents and voltages induced into loops due to nearby lightning

This paper presents the effect of considering propagation delays and displacement currents in the calculation of currents and voltages induced into loops due to nearby lightning flashes. Results from numerical calculation, based on a more complete electromagnetic formulation (Method of Moments — MoM) are compared with results from a quasi-stationary approach. It is shown that the voltages induced into loops by very fast currents, such as the subsequent lightning strokes, can be significantly influenced by the displacement currents and propagation delays. This effect depends also on the loop dimensions and its earthing configuration. In the example considered in this paper, the induced voltage reached a peak value one-third above the peak value calculated by magnetic induction only, besides exhibiting oscillatory wave forms. This increase in the magnitude and change of the induced voltage waveform may impact the design of clearance distances and, under specific conditions, may also jeopardize electronic equipment that otherwise would be considered safe based on the quasi-stationary approach.