MMC桥臂电抗器穿墙套管故障特性及保护策略

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

针对目前双极柔性直流输电系统模块化多电平换流器(MMC)中桥臂电抗器布置方案存在的故障过流问题,文中分析了桥臂电抗器布置在不同位置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;提出将桥臂电抗器布置在靠近直流连接点的方案,研究表明该方案能够有效限制阀侧接地故障的故障电流上升率,降低故障过电流水平,同时成本增加较少。但桥臂电抗器布置在靠近直流连接点后,现有保护策略不能及时发现桥臂电抗器穿墙套管发生的相间短路故障,会给换流器的安全运行带来隐患,因此文中提出一种桥臂电抗器穿墙套管相间短路保护策略,能有效识别桥臂电抗器穿墙套管相间短路故障。最后通过PSCAD/EMTDC对相关分析进行了仿真验证。

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.