MMC桥臂电抗器穿墙套管故障特性及保护策略

针对双极柔性直流输电系统模块化多电平换流器，分析了桥臂电抗器目前布置方案所存在的故障电流大问题，提出了将桥臂电抗器布置在靠近直流连接点的方案。分析了桥臂电抗器布置在不同位置时对换流器故障电流的影响，并推导了故障电流分量的数学表达式，研究表明桥臂电抗器布置在靠近直流连接点时能够有效限制阀侧接地故障时故障电流上升率，有效降低故障电流水平，同时不会带来较大成本增加。然而桥臂电抗器布置在靠近直流连接点后，其穿墙套管发生相间短路故障时现有保护策略并不能及时发现，给换流器的安全运行带来隐患，提出了一种桥臂电抗器穿墙套管短路保护策略，能够有效识别桥臂电抗器穿墙套管短路故障。最后通过PSCAD/EMTDC对相关分析进行了仿真验证。

Fault characteristics and protection strategy of MMC bridge arm reactor wall bushing

Aiming at the fault overcurrent problem existing in the current arrangement scheme of the bridge arm reactor in the modular multilevel converter (MMC) of the bipolar flexible DC transmission system, the influence of the bridge arm reactor in different positions on the converter fault current is analyzed in this paper, and the mathematical expression of fault current component is derived. A scheme of placing the bridge arm reactor near the DC connection point is proposed. The study shows that the arrangement of bridge arm reactor near the DC connection point can effectively limit the rise rate of fault current, reducing the overcurrent level of the bridge arm module without increasing larger costs. However, when the bridge arm reactor is arranged close to the DC connection point, the short circuit fault of the bridge arm reactor wall bushing cannot be detected in time by the existing protection strategy, which brings potential threats to the MMC. A protection strategy, which can effectively identify the short circuit fault of the bridge arm reactor wall bushing is proposed in this paper. Finally, the correlation analysis and protection strategy are verified by PSCAD/EMTDC simulation.