Lightning overvoltages on an overhead transmission line during backflashover and shielding failure

Analysis of induced voltages on transmission tower and conductors has been performed when a high voltage line is subjected to propagation of lightning transient. PSCAD/EMTDC software program is used to carry out the modelling and simulation works. Lightning strikes on the tower top or conductors result in large overvoltages appearing between the tower and the conductors. Two cases considered for these effects are: (i) direct strike to a shield wire or tower top; (ii) shielding failure. The probability of a lightning strike terminating on a shield wire or tower top is higher than that of a phase conductor. Voltages produced during shielding failure on conductors are more significant than during back flashovers. The severity of the induced voltages from single stroke and multiple stroke lightning is illustrated using the simulation results. The results demonstrate high magnitude of induced voltages by the multiple stroke lightning compared to those by single strokes. Analytical studies were performed to verify the results obtained from the simulation. Analysis of the performance of the line using IEEE Flash version 1.81 computer programme was also carried out.