Effect of Concentrated Tower Grounding System Modeling on the Minimum Backflashover Current and BFR of 150 and 400 kV Overhead Transmission Lines

The evaluation of the backflashover rate (BFR) of overhead power transmission lines requires knowledge of the minimum lightning current causing backflashover of line insulators. This work investigates the effects of concentrated tower grounding system modeling on this critical current as well as on BFR of typical 150 and 400 kV double-circuit power transmission lines through simulations using ATP-EMTP. Several models of concentrated grounding systems, which are based on a constant resistance or a current-dependent impulse resistance taking into account soil ionization effects, were employed in simulations; the low current and low frequency tower ground resistance was an influencing parameter. It is shown that the computed overvoltages arising across line insulators, therefore also the critical current and BFR, are significantly affected by tower grounding system modeling. BFR estimates are even more than 10 times lower for models that consider soil ionization effects.