Current Transformer

There are only 1 to several turns on the primary side, and the cross-sectional area of the wire is large, which is connected in series with the circuit under test. The secondary side has many turns and thin wires, which form a closed circuit with instruments with small impedance (current coils of ammeters/power meters). The operation of the current transformer is equivalent to the transformer with short circuit on the secondary side, ignoring the excitation current, and the ampere turns are equal. The current ratio of the primary winding current I1 to the secondary winding I2 of the current transformer is called the actual current ratio I1/I2 = N2/N1 = K. Excitation current is the main source of error. The accuracy grade of current transformer for measurement is 0.2/0.5/1/3, where 1 means that the ratio error is less than 1%, and there are also 0.2S and 0.5S grades. The accuracy grade of current transformer for protection is 5P/10P, and the marked composite error of 10P is less than 10%.