Investigation of bipolar block emergency in UHVDC convertor station caused by lightning stroke

It is noteworthy that bipolar block emergencies of the ±800kV UHVDC system in China happened twice within two years caused by lightning strokes. To recur and investigate the mechanism of such emergencies, lightning transient performance and relative electromagnetic interference (EMI) in the UHVDC system are investigated. Wide-band circuit models of major UHVDC equipments are set for calculation, while the lightning stroke shielding failure process and transmission corona loss are also considered during the simulation. By combining the fault records in the converter station and simulation results , possible ways of EMI into the secondary system produced by primary circuit lightning transient are analyzed. The results would help explain the cause of such bipolar block emergency and provide reference for protection methods of lightning caused EMI in UHVDC system.