Simulation of Lightning Strikes to 1000 kV UHV-AC Double-Circuit Transmission Lines

Lightning shielding failure (SF) is the main cause of tripping accidents in UHV transmission lines (TLs). SF assessment based on conventional electro geometric model (EGM) ignores the physical process of lightning progression and the influence of operating voltage. Therefore, it still leads to an underestimation of the shielding failure rate (SFR), which brings risks to the safety of TLs operation. In this paper, a numerical model of lightning attachment to 1000 kV double-circuit UHV-AC TLs based on the self-consistent leader inception and propagation model (SLIM) and FEM was developed. The downward leader was considered as a lossy conductor approaching the ground vertically at a constant velocity. The streamer charge and streamer length at the front of the upward leader were calculated using voltage distortion method (VDM). The process of lightning attachment to the TL has been simulated. In addition, the effect of the operating voltage of the phase conductors on the lightning attachment process was analyzed. The simulation results revealed that when the operating voltage was 0, only the upward leader can be generated on the GW. After the phase conductors charged with voltage, upward leaders may be generated on the GW and the upper phase conductor at the same time, which increased the SF risk of TLs. The upward leader on the GW has strong shielding effect on phase conductors, which inhibits the propagation of upward leader on phase conductors. For the upper phase conductor, the risk of SF appeared at the time when the voltage phase angle was 0°, 135°, and 270°.