Techniques for the Improvement of the Lightning Back-Flashover Performance of Double Circuit HVDC Lines

Abstract This paper addresses different issues regarding the lightning back-flashover performance of HVDC lines, especially regarding double-circuit configurations. In such configurations, two poles may present very similar flashover risks due to a lightning strike, leading to a double flashover. Therefore, it is of particular interest to investigate solutions to protect at least one circuit from flashovers and avoid the temporary loss of the transmitted power and the associated consequences to the system. In this work, electromagnetic transient models are implemented to investigate two solutions for the improvement of the lightning performance: the installation of surge arresters and the use of unbalanced insulation. The results are analysed thoroughly and the mechanisms and theoretical bases behind them are explained. In addition to the grounding resistance of the tower, the coupling between the conductors and the DC pole configuration within the tower also play a major role in determining the lightning back-flashover performance of a double circuit HVDC line. The installation of a single arrester can achieve a very significant improvement of the overall lightning performance of a tower. A proper implementation of an unbalanced insulation solution is very effective in limiting the incidence of double flashovers while maintaining an optimal overall performance.