Corona Effect on Insulator Voltages for a Direct Lightning Strike to a Phase Conductor

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 across insulators of a transmission line for direct lightning strikes to an upper phase conductor. In the simulation, 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 insulator-voltage peak due to the corona is significant only for the upper phase conductor. For a 10-kA peak current, the upper-phase-conductor voltage peaks are reduced by 26% and 21% for a positive stroke with 1-mu s-and 3-mu s-risetime currents, respectively, and those for negative-stroke case are reduced by 20% and 15%, respectively. For a 20-kA peak current, the corresponding upper-phase-voltage peaks are reduced by 32% and 25% for positive-stroke case, and those for negative-stroke case are reduced by 26% and 20%.