Preliminary Studies on the Characteristics of the Induced Currents in Simple Down Conductors Due to a Nearby Lightning Strike

A lightning strike in a neighborhood can induce significant currents in tall down conductors. Although the magnitude of current in this case is much smaller than that encountered during a direct strike, the probability of occurrence and the frequency content is higher. In view of this, appropriate knowledge of the characteristics of such induced currents is relevant for the scrutinization of the recorded currents. Considering these, the present paper makes a preliminary investigation into the basic characteristics of lightning-induced currents in simple tall vertical down conductors. The electromagnetic model is employed for the study, and NEC-2 is employed for the numerical field computations. Laboratory experiments with reduced-scale electromagnetic model of the system are employed to validate the numerical approach. The influence of important parameters has been investigated and highly insightful results obtained. The induced current is found to depend on the maximum rate of rise of the stroke current and its velocity of propagation, the height of the down conductor, and the footing impedance. The channel inclination and the distance between the channel and the down conductor have significant influence on the magnitude of the induced current. It is found that the radius of the down conductor is not very influential. The induced current due to a stroke on a nearby conducting object of considerable height can have different overall features