Analysis on the Characteristics of Lighting Invasion Wave in the Substation

Lighting impulse withstand level of transmission line and pollution flashover voltage of line insulator string can be enhanced by increasing the numbers of line insulator strings. However, improvement of line insulator insulation level may lead to insulation failure in the substation due to lighting invasion wave. In order to study the effect of line insulation strength on insulation coordination in substation, a surge arrester malfunction caused by lighting overvoltage in a 220kV substation was investigated. Based on the investigation results, simulation calculation models of lighting current, transmission line tower, insulator flashover and the fault transmission line was established. In the case of reverse strike, shielding failure and lighting without fault, waveforms of lighting invasion wave in the substation were simulated before and after the creepage adjustment of line insulator strings. The simulation results show that amplitude and front duration of lighting invasion wave increase with the improvement of line insulator insulation level, which lead to higher residual voltage and current in the surge arrester in the substation. Moreover, with the increase of line insulator strings number, amplitude of lighting overvoltage on the transmission line increases and lighting invasion wave can transmit to the substation from a further distance. The theoretical analysis demonstrates that increasing the diameter of insulator shed and spraying RTV on the surface of insulator are better methods against pollution flashover compared with creepage adjustment. Insulation level of equipments in the substation should be considered when increasing the numbers of insulator strings which can lead to surge arrester malfunction in the substation.