直流输电系统再启动功能改进措施

在高压直流长距离输电中，直流线路发生故障的概率较高，完善和合理使用再启动功能对提高直流输电系统的可用率意义重大。结合南方电网公司和国家电网公司直流工程的运行情况，分析了目前直流线路故障再启动功能现状，发现存在正常双极运行时负极再启动功能退出、可重启的故障范围小等问题。提出了改进建议:完善直流控制系统软件，加强两极之间再启动功能协调配合，在一极事故闭锁、直流线路故障及再启动期间，暂时闭锁另一极的再启动功能，防止两极同时或相继重启，避免因控制软件限制再启动功能的投入。并提出接地极线路接地故障和金属回线故障时，相应的接地极线路不平衡保护（GR模式）和直流线路横差保护的出口方式应由极闭锁调整为直流再启动。

Analysis and Improvement of Force Retard Function of HVDC Transmission Systems

High voltage DC (HVDC) transmission always used in long distance power transmission, and has higher possibility of line fault than short line. Based on the operation of HVDC projects in China Southern Grid and State Power Grid, DC line fault recovery (forced retard) is analyzed. The shortcomings, such as only one pole enable force retard function, and fault range that can initiate force retard is small, are presented. Enhancing HVDC control software function is one solution to this problem. If one pole is in pole block sequence, or during line fault, or in force retard sequence, force retard function of the other pole is disabled. By this way, two poles force retard or block simultaneously can be avoided, and force retard function is not limited by software anymore. Meanwhile, electrode line fault and metallic return line fault occurs, related HVDC protection function, such as electrode balance protection (60EL) and DC line transversal differential protection (87DCLT) should initiate force retard instead of pole block.