Investigation of lightning-induced overvoltages affected by the sag of the overhead transmission line

The overhead transmission lines have generally been considered as the straight lines in most research on lightning-induced overvoltages. Actually, the line is not straight and does not parallel to the ground level due to the sag produced by the weight of the line, etc. But the existing field-to-transmission line coupling models are created based on the hypothesis that the line parallels to the ground level. In this paper, the nonuniform overhead transmission line is approximated by cascaded series of many short elements of uniform lines parallel to the ground level. On the basis of this consideration, the field-to-transmission line model developed by Agrawal et al is valid, but the related equations need to be changed. Lightning-induced overvoltages affected by the sag are investigated. The results prove that the overvoltages are very intense comparison with the case of ignoring the sag of the transmission lines.