中文摘要：

对国内外多端直流系统的故障保护问题进行了综述。首先分析了基于电压源型换流器的多端直流系统故障的过程，研究了故障电流的特征和解析表达式。其次讨论了针对多端直流系统的继电保护原理，对电压／电流保护、纵联保护和行波暂态量保护进行的分析。然后针对多端直流系统的故障隔离问题，从选择性和恢复速度的角度对现有的策略进行了分析。最后，建议应当从加强有针对性的继电保护方案研究、重视故障快速恢复过程中换流器的性能以及关注测量环节对故障保护的影响3个方面展开研究工作，解决多端直流输电系统的故障保护问题。

英文摘要：

A survey on relay protection for multi - terminal DC systems at home and abroad is given. Firstly, the electromag- netic transient during fault is analyzed in a voltage source - based DC system, and the characteristics and analytical expression of fault current are studied. Secondly, for the issues on fault detection and isolation, many protection schemes, including cur- rent and voltage based protection, pilot protection and travelling wave or transient based protection, are discussed. Thirdly, the different fault isolation strategies are compared considering the power system requirements, such as rapidity and reliability. Finally, it is suggested that the further researches in three aspects, including novel algorithms for rapid fault detection in multi -terminal DC system, rapid fault restoration schemes based on converters with special structures and the influences from er- rors brought by DC current and voltage measurement, should be promoted.