Influence of the current front time representation on the assessment of backflashover occurrence of transmission lines by deterministic and probabilistic calculation approaches

Abstract This work addresses the impact on the backflashover occurrence in transmission lines of two different assumptions for representing the front time of return-stroke currents, namely a constant parameter, set as the median Td30 front time, and a varying parameter, determined from expressions correlating the front time and the peak current. To support the analysis, computational simulations assuming the HEM-DE deterministic approach and the ATP-DE-MC probabilistic approach based on the application of Monte Carlo method were developed, taking typical configurations of 138- and 230-kV single circuit transmission lines as case studies. The results show that the two methods of representing the current front time lead to similar critical currents and, therefore, percentages of backflashover. The observed difference in the results demonstrated to be larger only for those cases in which the percentage of backflashover is extremely low (of the order of 1% or lower), and, therefore, do not contribute to modify the calculated outage rate of the transmission line, in most cases.