中文摘要：

针对＂手拉手＂多端柔性直流配电系统的中压直流线路,设计了基于通信系统和直流断路器的继电保护方案。首先,介绍了柔性直流配电系统的配置和中压直流系统的故障特性;其次,针对系统危害较大的极间短路故障和小电阻接地故障,依靠电流量信息,根据每一保护安装处的线路电流状态矩阵,设计了能够识别故障类型和故障区间、在5ms内隔离故障的速动保护;针对系统可能出现的大电阻接地故障情况,设计了以电压不平衡量作为启动判据,根据同一保护安装处的正负极不平衡电流状态矩阵,实现故障定位和故障隔离的后备保护;并针对可能出现的保护拒动或通信装置失灵现象设计了第一级远后备保护和第二级远后备保护;还考虑了保护系统和控制系统的配合以保证非故障区域的正常供电。最后,通过PSCAD/EMTDC仿真验证了所提保护方案的有效性。

英文摘要：

A new protection scheme for the medium voltage DC line in the ＂hand-in-hand＂ multi-terminal flexible DC distribution network is designed based on the communication system and DC circuit breakers.Firstly,the configuration of the flexible DC distribution system and the fault characteristics of the medium voltage DC system are described.Then,aquickacting main protection scheme is designed for pole-to-pole faults and pole-to-ground faults with low fault resistance.The current information and current state matrix of each relay is used to identify the fault type and fault area to isolate the fault area within5 ms.Subsequently,a backup protection scheme is designed for possible pole-to-ground faults with high fault resistance.In such cases,the unbalanced voltage is taken as the startup criterion,with the fault area isolated according to the state of the unbalanced current of each relay.Besides,a first-step and a second-step remote backup protection each are designed in case of failures of DC circuit breakers and communication devices.Additionally,the cooperation between the protection system and the control system is taken into consideration to make sure the healthy area is supplied normally.Finally,simulation results in PSCAD/EMTDC verify the effectiveness of the proposed protection scheme.