Current transformer (CT) is an important electrical equipment in the power system. It has the function of isolation between high and low voltage systems and high to low voltage conversion. Whether the wiring is correct is of great significance for the protection, measurement, and measurement of the system. After reinstalling the CT, putting it into use or replacing the CT secondary cable, the relay protection personnel must confirm the correctness of the CT polarity. The following is a detailed introduction to CT polarity measurement

1. Polarity of CT（What is the polarity of a current transformer）What is it?

Polarity is the electromotive force induced by the primary and secondary coils under the same magnetic flux. The end with high or low potential is called the same polarity end.

The polarity of a current transformer (CT) refers to the relationship between the direction of current in its primary and secondary windings. According to regulations, the front end of the CT primary winding is marked as P1, and the tail end is marked as P2; The front end of the secondary winding is marked as S1, while the rear end is marked as S2. In wiring, P1 and S1, P2 and S2 are referred to as terminals of the same polarity. Assuming that the current I1 of a winding flows in from P1 at the first end and out from P2 at the tail end, the induced current I2 in the secondary winding flows out from S1 at the head end and ends up flowing in from S2 at the tail end. At this point, the direction of the magnetic flux generated in the iron core is the same, and this CT polarity symbol is called polarity reduction. On the contrary, it is called additive polarity. Unless otherwise specified, the polarity of ordinary current transformers is reduced.