Lightning protection of a compact MV power line sharing the same poles of a HV line

This paper deals with the assessment of the lightning performance of a double-circuit HV-MV overhead line. We focus on the protection of the 15-kV line with compact configuration that shares the same concrete poles of a 69-kV or 138-kV transmission line. Due to the presence of the HV conductors, the number of direct events to the multi-circuit line is higher than the one of a typical MV line alone in open terrain. The presence of the HV conductors and of the overhead ground wire reduces the induced overvoltages in the MV conductors due to indirect lightning events. For the considered configurations, the number of flashovers per year expected in the double-circuit line is lower than in a compact MV line in open terrain. It is shown that such a number depends mainly on the line withstand voltage, on the grounding resistance and on the presence of surge arresters, along with their location along the line. Such a dependence is quantitatively discussed in the paper.