Simple Expressions for External Wire Impedance and Admittance for Lightning Current Pulse Propagation in Buried Wires

Lightning surge propagation in buried cables and grounding systems is a subject of practical interest. In this paper we present simple expressions for external wire impedance and admittance that are valid for studying the lightning interaction with buried wires based on transmission line analysis. Buried wires can be either bare (counterpoise) or insulated (cables). Due to certain drawbacks of existing ground impedance expressions, a modified empirical ground impedance expression for buried wires is proposed. As it´s well known that lightning transients have frequencies between few kHz to few MHz, the ground impedance and ground admittance behavior is investigated for wide frequency range