A current transformer operates on the principle of electromagnetic induction. Its primary purpose is to measure high currents in power systems by converting them into lower, proportional values that are easier and safer to handle by measuring instruments and protective devices.
The CT consists of a primary winding, a magnetic core, and a secondary winding. The primary winding carries the actual system current and usually has just one or a few turns. The secondary winding, with many turns, is connected to measurement or protection equipment.
When current flows through the primary conductor, it creates a magnetic field around it. This magnetic field induces a voltage in the secondary winding according to Faraday's Law of Electromagnetic Induction. The secondary current is proportional to the primary current but reduced in magnitude based on the turns ratio between the two windings.
