On the Effect of Peak Current-Front Time Correlation Expressions for the Assessment of the Lightning Performance of Transmission Lines

This work evaluates the influence of considering correlation expressions between peak current and current front time of negative first return strokes on the assessment of the lightning performance of transmission lines in terms of backflashover occurrence. The analyses were performed considering computational simulations with the Hybrid Electromagnetic model and the integration method for transmission lines of voltage level of 230 kV and 500 kV. The results confirmed the estimation of higher critical currents when assuming the correlation expressions in relation to the use of the median current front time, though this difference does not impact significantly the resulting lightning performance. The larger differences occurred for those cases with probability of backflashover of the order of 1 % and lower. Also, the results indicated that the use of correlation expressions may lead to critical currents larger than 200 kA, which extrapolates significantly the available data of measured negative first stroke currents in instrumented towers. For these cases, truncating the analyses to a 200-kA critical current would lead to results in terms of backflashover probability compatible to those considering the median current front time.