零序电流互感器与普通电流互感器一样都是应用电磁感应原理工作的，但从它们的工作状态来看则有区别。普通电流互感器的一次绕组只与被保护线路的一相连接，并且一次绕组内的电流就是该相的负载电流，二次电流则是一次电流的相应值。而零序电流互感器则不然，它的一次绕组就是被保护线路的三相，在正常工作状态时，由于三相电流的矢量和等于零，铁芯中不会产生磁通，故二次绕组内也不会有感应电流。当被保护线路发生单相接地故障时，三相电流之和不再等于零，它等于每相零序电流的3倍，此时，互感器的铁芯中便产生感应磁通，二次绕组内将有感应电流，从而带动继电器使保护装置动作。

Zero sequence current transformer and the average current transformer is the basis of the principle of electromagnetic induction, but from their working condition is difference. Average current transformer primary winding and the protected line only one, and in a winding current is the phase of the load current, the secondary current is a current corresponding value. And zero sequence current transformer is not, it's a winding circuit of three phase is to be protected, in normal working state, because of three phase current vector and is equal to zero, won't produce magnetic flux in the core, so there will be no induced current in the secondary winding. When the protected circuit of single-phase earth fault occurs, the sum of three phase current no longer is equal to zero, it is 3 times of zero sequence current of each phase, at this point, the transformer is the core of induced magnetic flux, there will be induced current in the secondary winding, so as to drive the relay protection device. 

10kV零序电流互感器通常是用于使继电器动作来指示线路发生接地故障的保护装置。根据规程规定，要求在6~10kV的每路出线上都要装设零序电流互感器，以便利用发生单相接地故障时所产生的零序电流使保护装置动作，发出报警信号。

10 kv zero sequence current transformer is usually used to make relay action to indicate that the circuit ground fault protection device. Requirements according to the relevant provisions of the regulations in 6 ~ 10 kv to furnish on the road for each of the zero sequence current transformer, to take advantage of single-phase earth fault occurs the zero sequence current protection device, signal alarm. 

在小接地电流的电力系统中，发生单相接地时，只有很小的接地电容电流，而相间电压仍是对称的，其值也未变，因此可暂时运行。但这毕竟是一种故障，而且由于非故障相的对地电压要升高为正常时的根号3倍，故对线路绝缘是一种威胁，如果长此下去，可能引起非故障相的对地绝缘击穿而导致两相接地短路，引起线路开关跳闸，造成停电事故。为此，小接地电流系统（即中性点不接地或经阻抗接地的系统）中，必须装设无选择性的绝缘监视装置或有选择性的单相接地保护装置，以便在发生单相接地故障时，发出报警信号，使运行值班人员及时发现和处理。

In small grounding current of power system, when the single-phase grounding, only a small grounding capacitive current, voltage and alternate with is symmetrical, its value has not changed, so can run for the time being. But this is, after all, a failure, and due to the fault phase of voltage to rise to normal when the square root of 3 times, so the line insulation is a kind of threat, if the long, may cause the fault phase to ground insulation breakdown caused by two phase short circuit, circuit breaker tripping, causing blackouts. Therefore, small ground current system (that is, the neutral point grounding or by the impedance grounding system), selective insulation monitoring device must be installed with no or selective single-phase grounding protection device, so that the single-phase grounding fault occurs, a alarm signals, make the operation personnel on duty timely detection and treatment. 

有选择性的单相接地保护又称“零序电流保护”，它利用单相接地所产生的零序电流使保护装置动作，发出信号。当单相接地危及人身安全和设备安全时，则动作于跳闸。

Selective single-phase grounding protection is also called "zero sequence current protection", it USES single phase grounding of zero sequence current protection device, signal. When the single-phase grounding endanger personal safety and equipment safety, the action in the trip.