配电网发生故障后，故障点处流出的负序电流大部分流向系统侧，正常线路中流过的负序电流很小，各线路负序电流的故障特征区别度很大。此外，负序电流还具有不受中性点接地方式影响、抗过渡电阻能力强、不平衡分量易消除等优点。
In contrast, most of the negative sequence current flowing out of the fault point flows to the system side after the fault occurs in the distribution network. The negative sequence current flowing through the normal line is very small, and the fault characteristics of the negative sequence current of each line are very different. In addition, the negative sequence current has the advantages of not being affected by neutral grounding mode, strong resistance to transition resistance and easy elimination of unbalanced components.
但由于故障发生后的短暂时间内故障电流为瞬时变化的暂态分量，因此负序电流的提取成为主要问题。近年来比较常用的方法是移相法、瞬时分量法等。
However, due to the transient component of fault current in the short time after fault occurs, the extraction of negative sequence current becomes the main problem. In recent years, the commonly used methods are phase shifting method, instantaneous component method and so on