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A new technique for the calculation of the surge impedance of high-voltage towers is presented. The tower is represented by a four-terminal network for which the surge characteristics are determined by solving the transmission-line equations. The boundary conditions of voltage at the top and base of the tower are determined using a numerical solution of the electromagnetic field on a physical model of the tower. The physical model is a multiconductor geometrical model incorporating the conductors forming the main body, the slanted conductors, and the horizontal cross-arms where necessary. In the process of computing the terminal voltages and currents, soil resistivity effects are also taken into account. Surge impedance values obtained using this method are in good agreement with both published analytical formulae and field experiments.
Date of Publication: July 2006