What are the common types of current transformers used in three-phase MID energy meters?

In three-phase MID energy meters, current transformers (CTs) are essential for measuring electrical current. They come in various types, each suited to different applications and requirements. Here are the common types of current transformers used:

1. Wound Current Transformers
Description: 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 conductor, and the secondary winding provides a reduced current proportional to the primary current.
Applications: Wound CTs are used in situations where high accuracy and reliability are required. They are commonly found in high-voltage applications and are known for their precision in current measurement.
Advantages: High accuracy, stable performance, and capable of handling high currents.

2. Toroidal (Ring) Current Transformers
Description: Toroidal CTs have a ring-shaped core through which the conductor passes. The core is made of a magnetic material, and the secondary winding is wound around the core. These CTs do not have a primary winding but instead use the conductor as the primary element.
Applications: Toroidal CTs are often used for monitoring purposes in both low and medium voltage systems. They are popular for retrofit applications because they can be installed without disconnecting the conductor.
Advantages: Easy to install, compact, and suitable for both low and medium current measurements.

3. Bar-Type Current Transformers
Description: Bar-type CTs feature a bar-shaped core with the primary conductor passing through it. The secondary winding is wound around the bar. This design is used when direct connection to the primary conductor is required.
Applications: Bar-type CTs are used in high-current applications where the primary conductor itself acts as the primary winding. They are suitable for industrial and heavy-duty applications.
Advantages: High current measurement capability and durability in harsh environments.

4. Clamp-On Current Transformers
Description: Clamp-on CTs are designed to be easily attached or removed from a conductor without disconnecting it. They consist of a split-core that can be clamped around the conductor, with the secondary winding inside the clamp.
Applications: These are used for temporary or portable measurements, such as maintenance and testing. They are suitable for measuring currents in existing installations without disruption.
Advantages: Ease of installation and removal, non-intrusive, and ideal for temporary measurements.

5. Split-Core Current Transformers
Description: Split-core CTs have a core that can be split open, allowing the CT to be clamped around a conductor. This design facilitates installation without having to disconnect the conductor.
Applications: Split-core CTs are used in both low and medium voltage applications, especially where ease of installation and removal is essential.
Advantages: Convenient installation, flexibility, and suitability for retrofit applications.

The choice of current transformer for a three-phase MID energy meter depends on factors such as the current rating, installation requirements, and accuracy needs. Each type—wound, toroidal, bar-type, clamp-on, and split-core—offers distinct advantages and is selected based on the specific requirements of the measurement environment and application.