±500 kV张北柔性直流电网单极接地故障健全极母线过电压产生机理

Research on Producing Mechanism of Healthy Pole Bus Overvoltage for Monopolar Grounding Fault in ±500kV Zhangbei Flexible DC Power Grid

为实现我国间歇式清洁能源大规模、远距离消纳,服务低碳奥运,国家电网公司拟在张北建设±500 kV可再生能源柔性直流电网示范工程,是世界上首个具有网络特性的直流电网工程,且与以往工程不同的突出特点是采用架空线构成金属回线网络。建立了基于实际拓扑结构的过电压仿真模型,仿真了直流电网不同位置发生单极接地故障时各换流站的母线过电压水平,发现存在健全极过电压比故障极过电压更大的特殊现象。根据实际物理意义对健全极过电压进行分解,并分析影响程度,得出产生健全极过电压的根本原因是中性点电位抬升的结论;基于金属回线网络的电路结构,研究了接地极电阻、金属回线限流电抗器参数对中性点电位抬升的影响程度,为其他工程的绝缘配合提供理论指导。

To achieve large-scale long-distance accommodation of renewable energy in China, and low carbon service of Olympics, State Grid Corporation of China intends to build a 500 kV VSC-based DC grid pilot project, the world’s first DC grid project with network characteristics, in Zhangbei. Different from previous projects, as an outstanding feature, its overhead lines are used to form metallic return network in this project. Based on actual topology, this paper builds an overvoltage simulation model to simulate the overvoltage level of DC busbar when monopolar grounding fault occurs in different positions of the DC grid. It is found out that there is a special phenomenon of healthy pole overvoltage higher than faulty pole overvoltage. According to actual physical meaning, the healthy pole overvoltage is decomposed and the influence degree is analyzed. It is concluded that the fundamental cause of the healthy pole overvoltage is rise of neutral point potential. Based on circuit structure of metallic return, influence of the parameters of grounding resistance and metallic return current limiting reactor on rise of neutral point potential is studied, providing theoretical guidance for insulation coordination of other projects.