Zhangbei flexible DC power grid project will realize the engineering demonstration application of hybrid DC circuit breaker for the first time

and use the overhead line with higher failure rate as the transmission line

so the threat of fault overvoltage to the whole system is more serious.This paper takes the single-pole-to-grounding fault on the DC side of the flexible DC power grid as an example.The transient characteristics of single-pole-to-grounding fault with DC circuit breaker are studied.A simulation model of overvoltage of flexible DC power grid is built on PSCAD/EMTDC platform.The effects of the arrester voltage limiting factor

the closing time of the transfer branch submodule and the input mode of the arrester on the overvoltage level of the key nodes and equipment are analyzed by simulation.The results show that:overvoltage of DC bus

AC side of the converter

terminal of current-limiting reactor and metallic return in the converter station of flexible DC grid increases with the increase ofγ

and the absorbed energy of arrester decreases with the increase of the value ofγ;With the increase of the blocking time of branch module

the overvoltage of single-pole-grounding is reduced;The overvoltage between the terminal of current-limiting reactor produced by the input of surge arrester in sequence（with appropriate delay）is much smaller than that produced by the input of surge arrester at the same time

but have little influence on overvoltage of other equipment.The results can be used as reference for insulation design of flexible DC converter station and engineering application of DC circuit breaker.