CT Operated Meters are used extensively for measuring current and monitoring the operation of the power grid.
Along with voltage leads, revenue-grade CTs drive the electrical utility's watt-hour meter on virtually every building with three-phase service and single-phase services greater than 100 amps.
The CT is typically described by its current ratio from primary to secondary. Often, multiple CTs are installed as a "stack" for various uses.
For example, protection devices and revenue metering may use separate CTs to provide isolation between metering and protection circuits, and allows current transformers with different characteristics (accuracy, overload performance) to be used for the devices.