Assessing the Impact of DC Bipole Configuration on the Lightning Performance of a HVDC Transmission Line in terms of Backflashover

This work presents a discussion on the influence of both the polarity and position of the phase conductors (DC poles) of a double circuit 500 kV HVDC transmission line (TL) on lightning overvoltages developed across their line insulator strings and the corresponding lightning performance in terms of backflashover, considering computational simulations with the Hybrid Electromagnetic Model (HEM) and the Leader Progression Model (LPM). Several polarity arrangements of the DC poles were considered and their influence on the probability of backflashover occurrence due to negative downward lightning was assessed for tower-footing grounding impedances varying from 10 to 100 Ω. The study indicates the worst lightning performances for configurations B, C1 and D2, with critical current and backflashover probability varying from 96 to 49 kA and from 4% to 26%, respectively. These results show the importance of both the position and polarity of the phase conductors and tower-footing grounding impedance to define the HVDC TL performance, indicating the TL configurations with the lower phases with positive polarity as the one with worst lightning performance in terms of backflashover.