Influence of the Electromagnetic Pulse on the Overvoltages Due to Direct Lightning to Lines over Soils with Different Ground Conductivity

In medium-voltage distribution lines, lightning outages associated with indirect strokes are less frequent if these lines are equipped with a grounded shield wire and surge arresters are installed at close intervals. Thus, for this case, the lightning performance is mainly associated with the line response due to direct events. Recent analysis concerning medium voltage line equipped with a shield wire shows that the electromagnetic pulse radiated from the channel may enhance the overvoltage across insulators during direct strikes. This paper extends the analysis to lines over lossy soils, assuming different values of ground conductivity. The results indicate that the effect of the electromagnetic pulse needs indeed to be considered for an accurate lightning performance assessment of distribution lines with shield wire. On the one hand, the voltages across insulators increase as the soil conductivity decreases; on the other hand, it is shown that for direct strikes the difference between the voltage amplitudes calculated considering or not the LEMP contribution increases with the ground conductivity. Thus, appropriate modelling and relevant calculation tools availability is fundamental for the problem of interest.