Its core structure includes a primary winding, a secondary winding, an iron core, and insulation. The primary winding has very few turns and is connected in series with the measured main circuit; the secondary winding has more turns and connects to measuring instruments or protection devices.
The working principle of a current transformer is based on Faraday's law of electromagnetic induction, achieving current transformation through the turns ratio (transformation ratio) of the primary and secondary windings.
During operation, the magnetomotive force generated by the primary current is largely canceled out by the magnetomotive force generated by the secondary current, resulting in a very small excitation current.
When the current transformer is operating, its secondary circuit must remain closed, with a very low load impedance, operating close to a short circuit. Open circuits on the secondary side are strictly prohibited; otherwise, a dangerously high voltage will be induced on the secondary side, endangering equipment and personnel safety. Therefore, the secondary side must be reliably grounded during operation.