Introduction  In order to saving the transmission line corridor, the ±800 kV polar wires and electrode wires have been erected on the same tower in the highly urbanized areas such as Guangzhou and Shenzhen. There is an potential risk of bipolar blocking to HVDC system due to configuration of the same tower for both ±800 kV polar wires and electrode wires, but there is little research on it in China.

  Method  In this paper, the process of bipolar blocking caused by the lightning stroke in hybrid transmission lines was analyzed. Taking a project as an example, this paper calculated the lightning flashover rate of hybrid transmission line which erecting polar wires and electrode wires on the same tower by using the ATP-EMTP electromagnetic transient simulation program and the electrical geometric model. Based on this, several measures to reduce the risk of bipolar blocking were discussed.

  Results  The results show that the lightning flashover rate of hybrid transmission line is lower than the independent erecting DC lines. Measures of adding line lightning arrester in the electrode wires, replacing the electrode wires of tower cross-arm for the composite cross-arm, adding the electrode wires insulation level can effectively reduce the risk of bipolar blocking. By comparison of technology and economy, this paper recommended the case project is adopted to improve the electrode wires insulation level as the anti-accident measures. It is suggested that case project should be equipped with 15 pieces of 170 mm structure height insulator.

  Conclusion  This results provide certain technical support for the design of HVDC lines in congested areas.