Mechanism of ±800 kV HVDC converter abnormal block fault caused by lightning transient

• Based on wide band models of UHVDC system, characteristics of lightning transient and electromagnetic interference in the primary and secondary circuits are analyzed.
• The mechanism of one-pole DC line lighting strike caused bipolar block abnormal fault in UHVDC system is comprehensively investigated and explained.
• Precautionary measurements are proposed to prevent similar faults, and then applied and validated in the station.

Abnormal bipolar block accidents caused by single-pole DC line lightning strikes happened several times in the Yunnan-Guangdong ±800 kV UHVDC system in South China, which are serious threats to system security. In this paper, the lightning transients in the primary and secondary circuits of both faulted and sound poles in UHVDC system are studied, in order to reveal the mechanism of such accidents. Wide-band circuit models of major UHVDC equipment are developed for simulations. Characteristics of intruding lightning surges and DC filter transient currents on both poles are analyzed, while interferences coupled into secondary cables under different loads and sheath grounding conditions are calculated. The cause of the abnormal block of the sound pole is recognized and explained. Finally, countermeasures are proposed to prevent the recurrence of similar unintended events and to improve the interference immunity of UHVDC system.