交直流混联配电网换流变压器零序保护优化配置

Optimal Configuration of Zero-sequence Protection for Converter Transformer in AC/DC Hybrid Distribution Network

高压直流输电换流变压器零序保护原理应用于多端直流配电网时,因输配电系统拓扑结构及运行方式等因素的差异,该保护在特定条件下可能失去选择性而发生误动作。结合多端直流配电网的主接线拓扑和运行要求,研究了交直流侧的故障特征和传变机理,发现交流零序分量和直流零模分量在换流端间的相互传递是导致该问题的主要原因。随后,提出配置交流连接线路差动保护作为交流侧接地故障主保护,采用长延时的换流变压器零序保护作为整个直流场接地故障后备保护,且仅动作于报警的优化方案。最后,利用搭建的三端直流配电网PSCAD/EMTDC电磁暂态模型验证了所提方案的有效性。

When zero-sequence protection principle of the HVDC converter transformer has been applied to multi-terminal DC distribution network,due to the difference of the topology and operation mode of the transmission and distribution system, it may lose selectivity and malfunction under certain conditions. Combined with the main wiring topology and operation requirements of multi-terminal DC distribution network,the fault characteristics and transmission mechanism of AC/DC side are studied. It is found that the mutual transmission of AC zero-sequence component and DC zero-mode component between the converter ends is the main cause of this problem. It is proposed that the differential protection of AC connection line is used as the main protection of AC side grounding fault,and the zero-sequence protection of converter with long delay is used as the backup protection of DC field grounding fault and only acts on alarm. Finally,the effectiveness of the proposed scheme is verified by the PSCAD/EMTDC electromagnetic transient model of the three-terminal DC distribution network.