多端直流输电工程大地-金属回线转换策略

Strategy of conversion between ground return and metallic return in multi-terminal high voltage direct current transmission system

针对国内首个常规多端直流输电系统在不同功率水平进行大地回线至金属回线转换的过程中,金属回线转换开关(MRTB)保护动作,导致开关拒动及大地金属回线转换失败的问题,本文通过对大地金属回线转换过程中的电流回路进行分析,推导大地回线与金属回线共存时各个换流站电流的数学表达式,在此基础上分析MRTB拒动原因,并提出改进策略和运行建议,为工程设计和运行维护提供参考。最后,通过仿真证明了本文分析结论的正确性,表明所提改进策略具备工程应用推广价值。

In view of the problem that the metallic return transfer break(MRTB)protection acts in the process of ground-metallic return conversion at different power levels in the first conventional multi-terminal high voltage DC transmission system in China,which leads to switch rejection and ground-metallic return conversion failure,this paper analyzes the current loop in the process of ground-metallic return conversion.The mathematical expressions of each converter station current are deduced when earth and metal loop coexist.On the basis of these expressions,the reason of MRTB operation failure is obtained and the improvement strategies and operation suggestions are proposed to provide a reference for engineering design and operation maintenance.Finally,the correctness of the analysis conclusion is verified by the simulation,which shows that the proposed strategies has the engineering application promotion value.