电流互感器在交流回路中使用，在交流回路中电流的方向随时间在改变。电流互感器的极性指的是某一时刻一次侧极性与二次侧某一端极性相同，即同时为正、 或同时为负，称此极性为同极性端或同名端，用符号"*"、"-" 或"."表示。（也可理解为一次电流与二次电流的方向关系）。 按照规定，电流互感器一次线圈首端标为 L1，尾端标为 L2； 二次线圈的首端标为 K1，尾端标为 K2。在接线中 L1 和 K1 称为同极性端，L2 和 K2 也为同极性端。其三种标注方法如图 1 所示。 电流互感器同极性端的判别与耦合线圈的极性判别相同。较简单的方法例如用 1.5V 干电池接一次线圈，用一高内阻、 大量程的直流电压表接二次线圈。当开关闭合时，如果 发现电压表指针正向偏转，可判定 1 和 2 是同极性端， 当开关闭合时，如果发现电压表指针反向偏转，可判定1 和 2 不是同极性端。 The current transformer is used in ac circuit and the current in the ac circuit changes over time. At a certain moment the polarity of the current transformer is referring to the primary side and secondary side a polarity end polarity is the same, that is positive, or negative at the same time at the same time, according to the polarity as with side or side, with the same polarity with the symbol "*", "-" or ", "said. (also known as the direction of a current and a secondary current). In accordance with the regulations, the current transformer is marked by the first end of the coil and the tail is L2. The second coil is marked with the first end of K1 and the tail of K2. In the connection, L1 and K1 are referred to as the same polarity, and L2 and K2 are also polar. The three annotation methods are shown in figure 1. The polarity of the current transformer is identical to the polarity of the coupling coil. The simpler method, for example, USES a 1.5-v dry battery to pick up a coil, and the secondary coil is connected with a high internal resistance and a large range of dc voltmeters. When the switch is closed, if found voltmeter pointer forward deflection, can determine 1 and 2 is the same polarity side, when the switch is closed, if found voltmeter pointer reversed deflection, can determine 1 and 2 is not the same polarity.