A current transformer (CT) is an electrical device that scales a large primary current down to a smaller, standardized secondary current so meters, relays, and monitoring systems can measure it safely. In power systems, it is part of the instrumentation chain: the CT converts raw line current into a usable signal without requiring equipment to connect directly to the high-energy conductor.
CTs matter in cyber security because critical infrastructure depends on trustworthy measurements. If a CT is miswired, overloaded, saturated, or poorly calibrated, operators may see distorted data and make wrong decisions. In real defenses, engineers monitor CT burden, check calibration, and compare readings across devices to detect faults or tampering. In attacks against industrial systems, manipulation of measurement paths can hide overloads, delay fault detection, or create false confidence in system state. Reliable current measurement is therefore a control and security issue, not just an electrical one.