Estimation of Lightning Overvoltages and Critical Backflashover Current of a 150 kV Overhead Line due to Subsequent Strokes

Abstract:
This work deals with the computation of fast-front overvoltages arising across the insulators of a typical 150 kV over-head transmission line due to subsequent return strokes of negative downward lightning flashes. ATP-EMTP simula-tions were performed using the CIGRE lightning current waveform with median values for its parameters. Lightning strikes at the top of transmission towers are considered and the minimum peak current values causing backflashover are estimated. Results are compared with those obtained for first return strokes considering the statistical distributions for the current waveform parameters. The power-frequency ground resistance of transmission towers was varied to assess its influence. It is found that subsequent strokes cause higher overvoltage peak values, however, lower values at the overvoltage wavetail than first strokes with the same peak current. As a result, lower critical backflashover currents are obtained for subsequent strokes. The impact of rapid variations of the overvoltage waveforms due to subsequent return strokes on the behaviour of the leader development model used for insulator flashover prediction is discussed.