The simulation model for calculating the surge impedance of a tower

Tower surge impedance is an important parameter in the prediction of HV and EHV lightning outage rates. Several attempts have been made to measure it experimentally on full scale towers, and formulas to calculate this parameter have been proposed by Jordan, Wanger and Sargent, etc. However, the values of surge impedance calculated using these relationships are in poor agreement with each other and, in general, with the various measured values. This paper presents a simulation model of uneven distributing parameter for determining the surge impedance of towers by the Electromagnetic Transients Program (EMTP). This paper also demonstrates that the values so obtained describe the response of the tower adequately when a transmission line is struck by lightning, Furthermore, the simulation value of tower surge impedance is close to the actual test value and the relative error is ten percent.