Long distance flexible DC transmission line based on overhead line should be equipped with variety of protection equipment to avoid the transient overvoltages since the single-pole-to-ground fault of transmission often happens. This paper investigates the transient overvoltage mechanism under DC-side single-pole-to-ground fault of a half-bridge sub-module(HBSM)based modular multilevel converter(MMC)high voltage direct current(HVDC)system. The impact of the system configuration

equipment parameters and fault characteristics on the overvoltage is analyzed. Then the overvoltage suppression effects resulting from the converter blocking

surge arresters and DC circuit breakers(DCCB)are respectively examined. The research results show that the equipment parameters have the most significant impact on the peak value of the transient overvoltage

and when the protection scheme is used

the research result is again validated. Finally

this paper provides the optimal configuration of surge arresters to suppress the transient overvoltage.