Fast and reliable fault detection of DC distribution network is one of the key problems to be solved urgently for flexible DC distribution network. Based on the mathematical model of flexible DC distribution network

the fault characteristics of radial DC distribution network are analyzed in detail. In case of internal fault

the voltage differential on both sides of DC reactor which is installed at the head of line is less than zero

while the fault characteristics is opposite in case of external fault. On this basis

a kind of fault detection scheme based on voltage transient characteristic of DC reactor is proposed. The fast and reliable detection of internal and external fault is achieved by the use of voltage differential of DC reactor.The fault type can be distinguished accurately by using the transient voltage amplitude of positive and negative pole DC reactor. The proposed scheme can detect faults accurately and quickly only by using voltage and voltage differential on both sides of DC reactor. The scheme has simple principle

low hardware requirements and is easy to implement. Finally

a radial DC distribution network model is set up on PSCAD/EMTDC platform. The effectiveness and feasibility of the proposed scheme are verified by the simulation.