Lightning induced voltages on multiconductor power distribution line

Abstract

The magnitude and waveshape of the induced voltages on 33 kV, three-phase overhead power distribution lines of both single-circuit and double-circuit configurations due to a nearby lightning stroke have been computed. The effect of ground conductivity and the presence of multiple conductors on the magnitude and waveshape of the induced voltages are also studied. A comparison is made on the induced voltages for a single-conductor overhead line as well as for single- and double-circuit power distribution line configurations. It has been observed that the ground impedance as well as the presence of multiple conductors has a significant influence on the induced voltages. The first peak of the induced voltage at the line termination is found to be less when only ground conductivity is taken into account in the horizontal electric field computation. It is reduced further when ground conductivity is included in the calculation of both the horizontal electric field as well as in the coupling of field to overhead conductor. At the midpoint of the line, the influence of ground conductivity on the induced voltage is such that it increases the first peak. The first peak of induced voltage near the line termination gets reduced in the presence of other conductors in a multiconductor line, whereas it remains almost constant at the midpoint of the line. However, the second peak increases with number of conductors in both cases. It is also observed that the induced voltage on a conductor is reduced if the number of conductors in a power distribution line circuit are increased. In the time-domain coupling equation used for the computation of induced voltage, the ground impedance is usually represented by a convolution integral. The low-frequency approximation used for the transient ground resistance presents singularity as t→0. However, for the solution of the convolution integral a new approximate expression has been used, which circumvents the singularity.