A current transformer (CT) is a type of instrument transformer used to measure alternating current (AC) in electrical circuits. It works on the principle of electromagnetic induction and is designed to produce a proportional current in its secondary winding that is proportional to the current flowing through its primary winding.

Types of Current Transformers:

1. Wound Current Transformers:

   • Wound current transformers consist of a primary winding and a secondary winding wound around a magnetic core. The primary winding is connected in series with the circuit carrying the current to be measured, while the secondary winding is connected to the measuring instrument or relay. Wound CTs are commonly used for high-accuracy current measurement and protection in various applications.

2. Bar-Type Current Transformers:

   • Bar-type current transformers consist of a solid metal bar or conductor passing through the transformer's core. The conductor serves as the primary winding, and the secondary winding is wound around the core. Bar-type CTs are often used for busbar and cable applications where the primary conductor is not easily accessible.

3. Split-Core Current Transformers:

   • Split-core current transformers have a hinged or split design that allows them to be easily installed around existing conductors without the need to disconnect the circuit. They are commonly used for retrofitting or adding current measurement capabilities to existing electrical systems without interrupting power flow.

4. Rogowski Coil Current Transformers:

   • Rogowski coil current transformers use a flexible coil wound in a helical shape around the conductor carrying the current to be measured. They offer advantages such as flexibility, ease of installation, and wide bandwidth, making them suitable for applications requiring high-frequency current measurement or where space constraints limit the use of traditional CTs.

5. Window-Type Current Transformers:

   • Window-type current transformers have a split-core design with an opening or window in the core through which the primary conductor passes. They are commonly used for measurement and protection of large busbars, cables, and power lines, where it is impractical to disconnect the conductor for installation.

6. Oil-Immersed Current Transformers:

   • Oil-immersed current transformers are enclosed in a tank filled with insulating oil to provide insulation and cooling. They are often used in outdoor or high-voltage applications where insulation and heat dissipation are critical. Oil-immersed CTs are typically larger and more robust than dry-type CTs.

7. Gas-Insulated Current Transformers:

   • Gas-insulated current transformers use sulfur hexafluoride (SF6) gas as the insulating medium to provide high dielectric strength and insulation properties. They are commonly used in high-voltage substations and switchgear installations where space is limited, and reliability is paramount.

Each type of current transformer has its own advantages and limitations, and the selection of the appropriate CT depends on factors such as the application requirements, operating conditions, accuracy, and installation constraints.