双极柔性直流输电系统换流站交流三相接地故障分析及保护

随着电压等级和传输容量的提高,基于对称双极接线的多端柔性直流输电技术被越来越多地应用到实际工程中。换流站交流接地故障会对双极柔性直流输电系统产生严重危害,因此换流站的快速保护技术尤为重要。为此,首先分析了基于双极结构的多端柔性直流电网换流站交流三相接地故障的暂态特性,推导了故障电流中各组成成分的解析表达式。其次,根据故障暂态特性提出了一种适用于双极拓扑结构和金属回线接地方式的多端柔性直流电网快速保护策略。该保护利用换流器桥臂电流识别故障,动作速度快,可靠性高,并具有一定抗过渡电阻能力。在PSCAD/EMTDC仿真平台上搭建四端直流电网模型,仿真结果验证了故障暂态特性分析及所提出的保护方法在不同故障情况下的正确性。

Fault Analysis and Protection Scheme for Converter AC Three-phase Grounding of Bipolar HVDC Systems

With the increase of voltage level and transmission capacity, the bipolar wiring mode has become popular in actual high voltage direct current(HVDC) projects. The AC grounding fault of converter will cause serious harm to bipolar HVDC systems. Therefore, the fast protection scheme of HVDC system converters comes to be particularly important. In this paper, three-phase grounding fault transient characteristics in a multi-terminal DC power grid, based on bipolar wiring mode, are analyzed firstly. And mathematic expressions of each component of fault current are derived. Then, a fast protection scheme is proposed for bipolar HVDC system with metallic return according to the fault transient characteristics. Moreover, the scheme utilizes arm current of converter for fault identification and is verified to have the advantages of fast action speed, high reliability and the ability to resist the transition resistance. A four-terminal DC power grid model is established in PSCAD/EMTDC, and the validity of the protection scheme under different fault conditions is verified by simulation results.