Response of multiconductor power lines to nearby lightning return stroke electromagnetic fields

The calculation of voltages induced by indirect lightning on multiconductor overhead power lines has been the subject of several studies. The reported conclusions are not always in agreement with each other. In this paper, using a modeling procedure presented in a previous work, the authors study the shielding effect due to mutual coupling among the conductors of a three-phase power line and between the ground wires and the line conductors. The results are compared with those published by other authors, and explanations of the disagreements are given. Additionally, a simplified method to evaluate lightning-induced voltages on a multiconductor line from the values obtained for the single conductor case is presented, and a simple formula which gives the magnitude reduction of the induced voltages due to the presence of other conductors is derived. It is shown that, for the examined case, the derived simple formula gives practically the same results as those obtained using the rigorous procedure. The authors have also compared results obtained using the simplified formula proposed by Rusck to evaluate the protective ratio of a ground wire with their results, and they have found that the values predicted by the Rusck formula are about 6% lower than their own.