The current transformer is used in an AC loop where the direction of the current changes over time. The polarity of the current transformer means that the polarity of the primary side is the same as the polarity of one end of the secondary side at a certain moment, that is, it is positive at the same time or negative at the same time, and the polarity is called the same polarity end or the same name end. The symbol "*", "-" or "." indicates. (It can also be understood as the direction relationship between primary current and secondary current).