Transient voltages in transmission lines caused by direct lightning strikes

This work presents some results concerning the computational simulation of electromagnetic transients in transmission lines caused by direct strikes of lightning. The research has been carried out by application of a hybrid electromagnetic code developed by the authors´ research group. The presented results comprise mostly overvoltage waves developed across insulator strings or at ground wires due to the injection of impulsive current at the top of towers and at the shielding wires along span. The effect of adjacent towers on the developed overvoltage is evaluated. Sensitivity analyses are developed considering a range of values for soil resistivity, variable configurations of tower-footing and different injected current waveshapes. Some remarkable conclusions concern the grounding effective length for mitigation of overvoltage across the insulator strings, the relevance of midspan strikes and the importance of accurate representation of lightning current waveshape in the evaluation of lightning performance of lines.