A Current Transformer (CT) is an electrical device used to measure alternating current (AC) in a circuit. It works by converting the high current in the primary circuit to a lower, measurable value in the secondary circuit, making it suitable for monitoring, metering, and protection purposes in high-current systems. 

Measuring Current Transformers:
Used primarily for current measurement and metering purposes in electrical networks.
Provides a scaled-down version of the primary current that can be safely monitored using instruments such as ammeters, digital meters, and energy meters.
These CTs typically have a high degree of accuracy (class 0.1 to 0.5).

Applications:
Power monitoring and energy metering in industrial, commercial, and residential electrical systems.
Utility companies use them to monitor electrical consumption at various levels (from individual customers to the grid).
Substation monitoring.

Protection Current Transformers:
Used for protection relays in power distribution networks.
Designed to withstand short circuits and fault conditions.
These CTs often have a higher accuracy class, usually 5P (5% error at the rated current) or 10P (10% error at the rated current), which ensures reliability during fault conditions.

Applications:
Overcurrent protection for transformers, generators, and transmission lines.
Ground fault detection and differential protection for transformers and other critical equipment.
High-voltage transmission systems to protect equipment and systems from overloads or short circuits.

Rogowski Coil:
A type of CT that offers a flexible, non-intrusive measurement method, using a coil wound around the conductor without needing a magnetic core.
Ideal for measuring high currents where traditional CTs would be impractical or difficult to install.
Benefits include low power loss, flexible installation, and high-frequency response.

Applications:
Power quality monitoring in industrial and commercial applications.
High-frequency applications like motor control, variable speed drives, and high-voltage transmission lines.

Split-Core Current Transformers:
Applications:
Load monitoring in buildings, industrial plants, or electric vehicles.
Temporary metering during system maintenance or upgrades.

Solid-Core Current Transformers:
These have a rigid core and cannot be opened, requiring the circuit to be disconnected for installation.
Known for high accuracy and reliability, they are typically used in critical applications where the performance and accuracy of current measurement are paramount.

Applications:
Energy metering in substations or large industrial electrical systems.
Protective relaying and circuit protection in power distribution networks.