A current transformer (CT) is an electrical device used to measure alternating current (AC) by producing a reduced current proportional to the current in the circuit being measured. It works by transforming the high current flowing in a power line into a smaller, manageable current that can be safely used for monitoring, metering, and protection in electrical systems. CTs are often used in power distribution, transmission, and industrial electrical systems to ensure the accurate measurement of current without directly exposing measuring instruments to the high current in the primary circuit.

Current transformers are essential in applications where it's necessary to measure large currents and provide input to protective relays, circuit breakers, and monitoring equipment. They come in various types, including wound, toroidal, and bar types, depending on the specific application requirements. Their role in ensuring electrical safety, accurate current measurement, and system protection makes CTs a crucial component in energy management systems, electrical grids, and industrial power systems.