Current Transformers (CTs) are used in medium voltage (MV) and high voltage (HV) installations to provide electrical output images for protection devices, relays, and metering instruments. They are configured to provide current in their secondary windings that are related to the current flowing in their primary windings.

　　Transformers are used for measurement purposes as these transformers measure voltage, current, power, and energy. These are used in a variety of devices used in conjunction with ammeters, voltmeters, wattmeters, and energy meters. These transformers are divided into two main types, voltage transformers, and current transformers.

　　The working principle of current transformers is somewhat different when measured with standard voltage-type transformers. It contains two windings similar to ordinary voltage transformers. As long as the alternating current is provided throughout the primary section, an alternating magnetic flux can be generated, which will then excite the alternating current in the secondary section. In this form, the load impedance is very low. Therefore, the device works in short-circuit conditions. Therefore, the current through the second section is based on the current in the primary winding, not on the load impedance.

　　The two major application areas for current transformers are current measurement and protection. They are also used for isolation between measuring instruments and high-voltage grids. This not only ensures the safety of the user but also the safety of the terminal instrument in use. Current transformers are recommended for 40A or larger applications.