Overvoltages induced by lightning on overhead power and distribution lines with sag

Researchers working on the problem of the coupling of lightning electromagnetic fields to overhead lines have suggested that, if the formulation of the coupling problem given by Agrawal et al. is adopted, only the horizontal component of the electric field drives current in the direction of the line and that the vertical component induces current only at the vertical terminations. All of these studies assume that the wires are perfectly horizontal. In practice, however, the wires exhibit sag. A theoretical study of the effect of the sag in overhead conductors has been presented by Rubinstein but no experimental validation is available in the literature. In this paper, we report on the experimental test of the theory presented by Rubinstein. To carry out the test, an EMP (electromagnetic pulse) simulator and a model line were used. Measured and calculated waveforms are in reasonable agreement in amplitude and in wave shape, although the wave shape agreement worsens for larger amounts of sag. It is shown that the curvature of the wires results in a reduction of lightning-induced voltage magnitudes. Therefore, one can treat the perfectly horizontal wire case as a worst case