Current transformer polarity labeling
The current transformer adopts the method of reduced polarity labeling, that is, when the current in the same direction passes through the same polarity section of the primary and secondary windings at the same time, they generate the same direction of magnetic flux in the iron core. When the current is passed from the polar end of the primary winding, the current induced in the secondary winding flows out from the polar end. With the polar end as the reference, the primary and secondary current direction is opposite, so it is called the reduced polarity standard.
Because the current direction is opposite, and the resultant flux in the core is zero. Therefore, the following formula can be obtained:
N1Ip-N2Is=0(Originally the sum of the excitation ampere-turns is zero, but considering the flow direction of the two currents is different from the polar end, so the relationship between them is reduced).
Is=N1/N2*Ip
It can be seen that the direction of the primary and secondary currents is the same, is in phase, so we can use the secondary current to represent the primary current (consider the ratio conversion). This is the advantage of de-polarity labeling.
