多端直流大地回线和金属回线转换过程分析及策略研究

Analysis and Strategy Research on Transformation Between Ground Return and Metallic Return in the Multi-terminal DC Project

针对多端并联直流系统,以乌东德多端直流为例,分析了大地回线和金属回线相互转换的过程,并对转换过程中各端换流站的直流电流返回回路及流经转换开关电流的变化进行解析。通过PSCAD仿真,比较不同操作顺序下大地回线和金属回线相互转换时转换开关电流的情况,针对转换电流可能超过转换开关开断电流能力的问题,提出优化转换操作顺序的建议。分析结果可为多端直流输电工程的设计、运维提供有益参考。

Aiming at the multi-terminal parallel DC system,taking Wudongde multi-terminal DC as an example,the process of conversion between the earth circuit and the metal circuit was analyzed.The change of the DC current return loop of the converter station at each end and the current flowing through the transfer switch during the conversion process was analyzed.Through PSCAD simulation,the situation of transfer switch current was compared when the earth loop and metal loop were switched to each other in different operating sequences.Aiming at the problem that the conversion current may exceed the breaking current capability of the transfer switch,suggestions were made for optimizing the sequence of the conversion operation.The analysis results could provide useful reference for the design,operation and maintenance of multi-terminal DC transmission projects.