On the choice of current wavefront parameters to assess the lightning performance of transmission lines: the use of correlation expressions and median parameters

Inhalt:
A discussion on the choice of current wavefront parameters to be applied on calculation procedures for the assessment of the lightning performance of transmission lines in terms of backflashover is presented, considering computational simu-lations with the CIGRE concave waveform and two distinct approaches: (i) the correlation among peak current, front time and maximum steepness, and (ii) front time assumed as an independent and constant parameter equal to the median value. The results considering simulations with 138 kV and 500 kV TLs indicate that adopting concave current waveforms with front time equal to the median Td30 leads to critical peak currents and probability of backflashover very similar to those obtained when the correlation among front time parameters is taking into account, mainly for those conditions of interest to the lightning performance assessment. The larger differences occurred for those cases with probability of backflashover of the order of 1% and lower. On the other hand, the resulting critical maximum steepness diverge in most of cases for those expected by the correlation expressions, but this behaviour did not impact the calculated lightning performance.