ABB 塑壳断路器附件，外置中性线电流互感器 CT EXT NEUTRAL 40A XT4；
电力系统中广泛采用的是电磁式电流互感器(以下简称电流互感器)，它的工作原理和变压器相似。电流互感器的原理接线，如左图所示。
The electromagnetic current transformer (hereinafter referred to as current transformer) is widely used in power system, and its working principle is similar to that of transformer. The principle of wiring of current transformer, as shown on the left.
电流互感器的特点是： (1)一次线圈串联在电路中，并且匝数很少，因此，一次线圈中的电流完全取决于被测电路的负荷电流．而与二次电流无关；(2)电流互感器二次线圈所接仪表和继电器的电流线圈阻抗都很小，所以正常情况下，电流互感器在近于短路状态下运行。
The characteristics of the current transformer are: (1) the primary coil is connected in a circuit with few turns, so the current in the primary coil is entirely dependent on the load current of the measured circuit. It has nothing to do with the two current; (2) the current coil impedance of the instrument and relay of the two coil of the current transformer is very small, so it is normal. Under the short-circuit condition, the current transformer runs.
电流互感器一、二次额定电流之比，称为电流互感器的额定互感比：kn=I1n/I2n
The ratio of the one or two times rated current of the current transformer is called the rated mutual inductance ratio of the current transformer: kn=I1n/I2n.
因为一次线圈额定电流I1n己标准化，二次线圈额定电流I2n统一为5(1或0.5)安，所以电流互感器额定互感比亦已标准化。kn还可以近似地表示为互感器一、二次线圈的匝数比，即kn≈kN=N1/N2式中N1、N2为一、二线圈的匝数。
Because the rated current I1n of one coil has been standardized, the rated current of the two coil is 5 (1 or 0.5), so the rated mutual inductance of the current transformer has also been standardized. Kn can also be approximately represented as the number of turns of the one or two coils of the transformer, that is, the turns of N1 and N2 in the kn kN=N1/N2 kN=N1/N2 are the turns of the coils.
电流互感器的作用就是用于测量比较大的电流。
The function of current transformer is to measure larger current.