原理：零序电流保护的基本原理是基于基尔霍夫电流定律：流入电路中任一节点的复电流 的代数和等于零。在线路与电气设备正常的情况下，各相电流的矢量和等于零，因此，零序电流互感器的二次侧绕组无信号输出，执行元件不动作。当发生接地故障时的各相电流的矢量和不为零，故障电流使零序电流互感器的环形铁芯中产生磁通，零序电流互感器的二次侧感应电压使执行元件动作，带动脱扣装置，切换供电网络，达到接地故障保护的目的。    作用：当电路中发生触电或漏电故障时，保护动作，切断电源。   使用：可在三相线路上各装一个电流互感器，或让三相导线一起穿过一零序电流互感器，也可在中性线N上安装一个零序电流互感器，利用其来检测三相的电流矢量和。  在三相四线电路中，三相电流的相量和等于零，即Ia+Ib+IC=0。如果在三相四线中接入一个电流互感器，这时感应电流为零。当电路中发生触电或漏电故障时，回路中有漏电电流流过，这时穿过互感器的三相电流相量和不等零，其相量和为：Ia+Ib+Ic=I(漏电电流)，这样互感器二次线圈中就有一个感应电压，此电压加于检测部分的电子放大电路，与保护区装置预定动作电流值相比较，如大于动作电流，即使灵敏继电器动作，作用于执行元件掉闸。这里所接的互感器称为零序电流互感器，三相电流的相量和不等于零，所产生的电流即为零序电流。

Principle: the basic principle of zero sequence current protection is based on Kirchhoff's current law: the algebraic sum of the complex currents of any node in the inflow circuit is equal to zero. When the line and the electrical equipment are normal, the vector of each phase current is equal to zero, therefore, the two side winding of the zero sequence current transformer has no signal output, and the actuating element does not move. When the current vector grounding fault and fault current is not zero, the flux ring cores of the zero sequence current transformer, two secondary side induction voltage of zero sequence current transformer so that the actuator action drives the tripping device, switching power supply network, to achieve the purpose of grounding fault protection. Role: when the circuit occurs electric shock or leakage fault, protection action, cut off the power supply. Use: in the three-phase line are respectively provided with a current transformer, or let the conductor through a three-phase zero sequence current transformer, also can install a current transformer in the neutral line N, using the detected current and phase vector. In a three-phase four wire circuit, the phasor of the three-phase current is equal to zero, that is, Ia+Ib+IC=0. If a current transformer is connected to the three-phase four wire, the induced current is zero. When the electric shock or leakage fault in the circuit, a leakage current flowing through the loop, then through the three-phase current transformer phase and the phase ranging from zero, and the amount of: Ia+Ib+Ic=I (current transformer), so the two coils have an induction voltage, the voltage on the part of the electronic detection the amplifying circuit, and protection device with predetermined compared action current value, such as greater than the current action, even if the sensitive relay action, acting on the actuator switch off. The mutual inductor is called zero sequence current transformer, and the phase current of the three-phase current is not equal to zero, and the current produced is zero sequence current.