What does a current transformer do?

A current transformer is designed specifically to measure large AC current flows by converting them to a smaller, manageable output current that can be safely measured by standard instrumentation. This is accomplished by utilizing the principle of electromagnetic induction, where the primary winding (which is connected to the high current circuit) generates a magnetic field, inducing a proportionally small current in the secondary winding.

The output produced by the transformer is typically a much smaller value, allowing for accurate measurements without subjecting sensitive instruments to the risks associated with high current levels. This feature is crucial in electrical systems for monitoring and protection, as it helps in providing real-time current measurements without needing specialized equipment that can handle large currents directly.

In contrast, the other choices pertain to functions that are either not related to current transformers or describe different types of devices used in electrical circuits. For instance, measuring high-frequency signals or acting as a circuit breaker involves different mechanisms and applications not applicable to current transformers.