In order to quickly and accurately identify the DC side faults in modular multilevel multiterminal flexible DC transmission lines, this paper presents a bi-polar fault detection method for modular multilevel multiterminal flexible DC transmission lines based on time characteristics. The traveling wave and converter voltage fluctuation under the condition of bipolar fault are analyzed. The difference of the first voltage traveling wave between the fault line and the non-fault line is used to detect the fault quickly. The rationality of bipolar fault detection method is verified by simulation. The results show that the method is not affected by the transition resistance and the fault distance has very little influence on it, so it can detect the bipolar faults quickly.
