Abstract:The flexible medium-voltage dc distribution network has the characteristics of flexible operation mode, safe and simple power flow control and good economy, etc. It is an important part of the future construction of dc power network. However, the short-circuit current of the medium-voltage dc distribution network rises rapidly without natural zero crossing, and the over-current resistance of IGBT and other components in the converter station is extremely poor, so the relay protection scheme is required to be able to act quickly and reliably. As the medium voltage dc distribution network mostly uses cables as transmission lines, the structure and environment of the cable lines have great influence on the performance of current differential protection. In order to solve the problem of poor performance of current differential protection in flexible medium-voltage dc distribution network with cable lines, a new type of current differential protection scheme based on Bergeron model is adopted, and compared with conventional current differential protection, the quick action of current differential protection is obviously improved.