涌流工况下换流变压器零序差动保护误动对策

针对高压直流输电工程中换流变压器零序差动保护误动的案例，采用基于工程实际参数的高压直流输电仿真模型，对换流变压器外部故障切除恢复性涌流及空载合闸励磁涌流导致中性线零序电流幅值较大且衰减缓慢的现象进行了仿真分析。通过识别中性线零序电流与自产零序电流波形呈现出的相似度特征在涌流工况和区内故障时的差异，提出了基于零序电流动态时间弯曲距离的换流变压器零序差动保护新判据。经仿真算例和录波案例验证，该判据在各类区内故障时具有与传统零序差动保护相同的保护范围及抗过渡电阻能力，可以正确辨识涌流工况下电流互感器传变异常引起的虚假差动电流，进而降低零序差动保护误动风险。

Countermeasures for Mal-operation of Zero-sequence Differential Protection of Converter Transformer Under Inrush Current Condition

Aiming at the case of mal-operation of zero-sequence differential protection for the converter transformer in the high voltage direct current (HVDC) transmission project, this paper analyzes the phenomenon that the neutral-line zero-sequence current has a large amplitude and decays slowly under the recovery inrush current condition caused by removal of external faults and the inrush current condition caused by the energization of unloaded converter transformers, based on the HVDC simulation model using actual engineering parameters. By identifying differences in similarity characteristics between the waveforms of neutral-line zero-sequence current and the self-produced zero-sequence current under inrush current and internal fault conditions, this paper proposes a new criterion of the zero-sequence differential protection for converter transformers, based on the dynamic time warping (DTW) distance of zero-sequence current. The simulation and recorded cases show that the criterion has the same operation performance as the conventional zero-sequence differential protection in aspects of protecting range and transition resistance endurance ability during various internal faults. The false differential current caused by abnormal transmission of current transformers under the inrush current condition can be correctly identified, and the risk of mal-operation of zero-sequence differential protection can be reduced.