不同故障下特高压换流变压器差动保护动作特性分析

换流变压器作为高压直流输电系统中重要的电气设备，其继电保护对保障系统安全运行有着非常重要的作用。目前，变压器大多采用基于二次谐波制动的差动保护闭锁方案。特高压直流输电系统中换流器的非线性导致换流变压器和普通电力变压器差动保护存在差异。通过构建相应的短路电流流通路径，研究了换流变压器差动电流在区内单相接地短路故障、区内相间短路故障以及整流侧阀短路故障情况下的特点。研究结果表明，换流变发生区外故障时差动保护不会误动，但换流变发生区内故障时差动保护可能拒动。

Research on the characteristics of ultra-high voltage converter transformer differential protection under the internal and external faults

Converter transformer is the most important equipment in HVDC system, and its differential protection plays a significant role to guarantee the safety operation of HVDC system. At present, the second harmonic restraint method is usually adopted in converter transformer differential protection for blocking inrush currents. The converter adopted in ultra HVDC system is non-linear component, which results in differences between protective performance of the converter transformer and the common power transformer. This paper makes detailed analysis on the different fault characteristic of the converter transformer by constructing relevant short circuit current flow path, which includes the internal single phase to ground fault, internal phase to phase fault, and the valve fault in rectifier. The research results show that the differential protection of converter transformer will not mal-operate during an external fault, but it may refuse to operate when internal faults. This work is supported by Key Project of Smart Grid Technology and Equipment of National Key Research and Development Program of China (No. 2016YFB0900600).