FDTD simulation of direct lightning strike to a phase conductor: Influence of corona on transient voltages at the tower

• A simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of transient voltages at the tower of a transmission line for direct lightning strikes to an upper phase conductor.
• Effect of corona on transient voltages is examined.
• The progression of corona streamers from the conductor is represented as the radial expansion of cylindrical conducting region.
• The reduction of transient-voltage peak due to corona is not very significant.

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of transient voltages at the tower of a transmission line caused by direct lightning strikes to an upper phase conductor. In the simulations, three 40-m towers, separated by 300 m, with one overhead ground wire and three phase conductors are employed. Corona is assumed to occur only on the upper phase conductor struck by lightning. The progression of corona streamers from the conductor is represented as the radial expansion of cylindrical conducting region around the conductor. The reduction of transient-voltage peak due to corona is not very significant, so that the voltage at the nearest tower exceeds the insulation level of 66/77 kV power line considered in this paper. For a 10-kA peak current, the upper-phase-conductor voltage peaks are reduced by 26% and 21% for a positive stroke with 1-μs- and 3-μs-risetime currents, respectively, and those for negative-stroke case are reduced by 18% and 13%, respectively. For a 20-kA peak current, the corresponding upper-phase-voltage peaks are reduced by 32% and 25% for the positive-stroke case, and those for the negative-stroke case are reduced by 22% and 15%.