张北柔直电网单极接地故障短路电流计算方法及接地策略

Short Circuit Current Calculation Method and Grounding Strategy of Pole-to-Ground Fault in Zhangbei Flexible DC Power Grid

基于模块化多电平换流器的柔性直流电网在消纳可再生能源等方面具有广阔前景,而单极接地故障是柔性直流电网中最常见故障,因此故障电流水平的研究对电网规划和设计具有重大意义。分析了张北直流电网单极接地故障的放电机理,通过阻抗高频特性提出故障电流计算方法,所提方法对真双极系统直流侧单、双极短路故障均适用,且最大误差不超过4%,为系统绝缘配合、接地网设计提供指导。根据对短路电流特性和直流电网接地极、线路侧重的分析,提出了直流电网接地策略,显著降低了直流电网故障电流水平。所提计算方法和接地策略在PSCAD/EMTDC仿真平台上得到了验证。

The flexible DC grid based on MMC has broad prospects in absorbing renewable energy,and the pole-to-ground fault is the most common fault in the flexible DC grid.Therefore,the research on the fault current level is of great significance to grid planning and design.The discharge mechanism of unipolar ground fault in Zhangbei DC power grid is analyzed,and the fault current calculation method is proposed based on the impedance high-frequency characteristics.The proposed method is applicable to both single and bipolar short-circuit faults on the DC side of the true bipolar system.and the maximum error does not exceed 4%,which provides guidance for system insulation coordination and grounding grid design.Based on the analysis of the short-circuit current characteristics and the grounding pole and line emphasis of DC grid,the grounding strategy of the DC grid is proposed,which significantly reduces the DC grid fault current level.The proposed calculation method and grounding strategy have been verified on the PSCAD/EMTDC simulation platform.