What is a current transformer?

A current transformer (CT) functions as a vital instrument in electrical systems, converting high currents into proportional, lower currents through a specified transformation ratio. Operating much like a traditional transformer, the CT diverges in its primary purpose, focusing on current modification rather than voltage alteration. Originally termed a 'converter', its nomenclature evolved alongside the development of devices specifically dedicated to converting direct current to alternating current.

Central to the CT's operation is the principle of mutual inductance, facilitating the seamless transformation of current levels. Typically, the primary winding of a CT integrates into the circuit necessitating measurement, protection, or control, while the secondary winding links to the current coil of the associated measuring, protection, or control apparatus. This configuration effectively isolates the high-voltage primary circuit from the lower-voltage secondary circuit, ensuring safety and accuracy in measurements.

During standard operation, the ratio of primary to secondary rated currents in a CT inversely correlates with the respective number of winding turns. Additionally, efforts are make to minimize the phase difference between primary and secondary currents, ideally approaching zero for optimal performance and reliability.