3-D FDTD Analysis of Lightning-Induced Voltages in Distribution Lines Due to Inclined Lightning

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angleθ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only minor differences on the peak voltage, the voltage profile along the line becomes asymmetric. In the multiphase line, the influence of the angle θ on the voltage becomes similar to that in the single conductor line. These results clearly indicate that the lightning inclination should be considered for an accurate evaluation of lightning-induced voltages.