Lightning-induced voltages on power lines: advances in modelling, computational effort optimization and innovative tools for the protection of overhead distribution lines

The continuous growth of MV overhead distribution systems requires a constant improvement in terms of security and power quality. One of the most critical event that can cause the fault of a distribution line is represented by the atmospheric discharges and, among them, the most dangerous one is no-doubt the lightning stroke. In the transmission and distribution systems, lightning transients can be caused by either direct or indirect strikes. Indirect strikes are much more frequent than direct strikes and can cause flashovers, especially when the line insulation level is low. The computation of the lightning induced-voltages (i.e. the one related to the indirect strikes, which represent the most critical issue in distribution systems) is a very complicated task for two main reasons: 1) the number of uncertain parameters is high: it involves a correct representation of the current that flows in the lightning channel as well as a correct representation of the soil conductivity where the power line is located. 2) The computational complexity of the calculations that allow evaluating the final overvoltage is high because in this case we are dealing with the computation of electromagnetic fields and with the effect of such fields on the power line. Concerning the protecting measures the most widely employed are the use of shield wires, surge arrester and the increase of the line insulation level. This thesis aims at improving the problem of the lightning-induced voltages in overhead distribution lines in terms of three main concepts: 1) innovation of the existing models, 2) optimization of the computational effort and 3) introduction of innovative tools for the protecting scheme. In this framework, the thesis proposes a new channel-bae current model (1) , an analytical technique for the electromagnetic fields computation (2) , a new scheme for the lightning-induced voltages computation (2), a new approach for reducing the computational effort of the lightning performance computation (2 and 3) and an innovative approach for the evaluation of the mitigation effect of shield wires on the lightning-induced voltages (3).