Effects of Approximating Recorded Lightning Currents With CIGRE Waveforms on Computed Fast-Front Overvoltages and Critical Lightning Currents Causing Flashover to Overhead Transmission Lines

This work investigates through simulations with the ATP-EMTP program the application of recorded lightning current waveforms to the estimation of fast-front overvoltages and critical lightning currents causing flashover to overhead transmission lines. Typical lines are evaluated with both horizontal (single-circuit) and vertical (double-circuit) phase configurations and AC voltage from 66 kV up to 765 kV. Backflashover as well as shielding failure flashover simulations were performed for several recorded first return-stroke current waveforms of negative downward lightning flashes, as reported in literature. Their approximations with the widely-used CIGRE lightning current waveform were also employed in simulations. CIGRE waveforms, considering the statistical distributions of the front time, maximum steepness, and time to half value, were used as well. A comparison between double-peak waveforms, composed of seven Heidler functions, and their CIGRE approximations is made. The latter generally yield conservative values of overvoltages and critical backflashover currents. The leader development models used for assessing the behavior of insulators and long air gaps under fast-front overvoltages are discussed regarding the criterion for the termination of leader propagation yielding withstand of line insulation.