Impulsive voltages induced into internal cabling of buildings hit by lightning

This paper presents the effects of propagation delays and displacement currents in the calculation of currents and voltages induced on metallic cabling inside buildings hit by 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 voltages induced by very fast currents, such as those from subsequent lightning strokes, can be significantly influenced by displacement currents and propagation delays. These effects depend on the cabling geometry and its grounding configuration. In the examples considered in this paper, the induced voltages reached peak values much higher than those calculated by magnetic induction alone, besides exhibiting oscillatory wave forms. The increase in the magnitude and the 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.