Comparison of the transmission line and scattering models for computing the HEMP response of overhead cables

The author discusses the use of transmission line and electromagnetic scattering models for computing the induced currents on long above-ground electrical cables, subjected to a transient plane wave excitation. The pertinent equations for determining the excitation electric field along the cable are summarized, along with the expressions which relate the line current to the excitation field. For the transmission line case, the cable current can be expressed in terms of per-unit-length impedance and admittance parameters which are functions of only the line geometry and the frequency. For the scattering case, similar line parameters can be inferred from the form of the solution for the current, but with the line parameters depending on the angles of incidence. Several numerical calculations of the line responses are provided, and these indicate that the transmission line analysis appears to provide response estimates which are smaller than those obtained using the more accurate scattering theory