Protective Effect of Shield Wires Against Direct Lightning Flashes to Buried Cables

The protective effect of a shield wire against direct lightning flashes to a buried power cable has been clarified in this paper. The finite-difference time-domain (FDTD) method is used in the investigation. The FDTD model considers a 1-km-long insulated cable protected by a shield wire, and a lightning strike right above them. The model has been validated by comparing its results with experimental results available in the literature. The computed results show that the presence of the shield wire can effectively prevent the cable from being directly struck by the lightning flash. The voltage across the cable insulation at the striking point depends on the ground resistivity (the higher the resistivity, the higher the voltage), but this dependence is not linear. It is also shown that the soil surface ionization is relevant to the current delivered to the shield wire and to the voltage developed across the cable insulation. On the other hand, the soil ionization around the shield wire has negligible effects. The intrinsic resistance of the shield wire does not influence significantly the peak voltage across the cable insulation, but it influences its duration (the higher the intrinsic resistance, the longer the voltage duration).