Induced overvoltage while ±500 kV pole line and neutral line using common-tower

Combined with the actual situation that bipolar block comes from lightning on DC pole line on one ±500 kV HVDC project in China Southern Power Grid, the recurrence was given by electromagnetic transient analysis software EMTDC/PSCAD. We researched and analyzed that the neutral line in common-tower caused the induced over-voltage and insulation flashover, leading to DC system bipolar block, when HVDC pole line was hit by lightning in the DC system. The results show that, in the common-tower with the pole line and neutral line, due to the big insulation difference, when HVDC pole line is hit by lightning, the neutral line on the common-tower will produce very high induced over-voltage and lightning wave propagation process, and the induced voltage of the neutral line has a cumulative effect to reach its insulation levels many times, thus, multi point flashover occurred in the insulation of neutral line. The results of this study on the common-tower with different voltage grade line are of significance to the design.