正常情况下，由于零序电流互感器一次侧三相电流对称，其相量和为零，铁芯中不会产生磁通，二次绕组中没有电流。
Normally, due to the symmetry of the three-phase current in the primary side of zero sequence current transformer, its phasor and phase are zero. There is no flux in the core and no current in the secondary winding.
当系统中发生单相接地故障时，三相电流之和不为零，一次绕组将流过电流，此电流等于每相零序电流的3倍，因此在铁芯中出现零序磁通，该磁通在二次绕组感应出电动势，二次电流流过断电器，使之动作。
When a single-phase grounding fault occurs in the system, the sum of three-phase currents is not zero, and the primary winding will flow through the current, which is equal to three times the zero-sequence current per phase. Therefore, zero-sequence flux appears in the core. The flux induces the electromotive force in the secondary winding, and the secondary current flows through the breaker to make it operate.
实际上，由于三相导线排列不对称，它们与二次绕组间的互感彼此不相等，零序电流互感器的二次绕组中不平衡电流流过。
In fact, due to the asymmetric arrangement of three-phase conductors, the mutual inductances between them and secondary windings are not equal, and the unbalanced current flows through the secondary windings of zero-sequence current transformer.