Current transformers (CT) are devices used to measure alternating current (AC) by producing a reduced current proportional to the current flowing in the primary circuit. They are commonly used in electrical systems to safely monitor and measure high currents. Current transformers generally consist of a primary winding, usually a single wire or bus bar through which current flows, and a secondary winding wound around a magnetic core.
The design ensures that the measured current is reduced to a lower, manageable level for measuring or monitoring equipment.
A current transformer operates by using electromagnetic induction to produce a secondary current proportional to the current in the primary circuit. The primary current flowing in the conductor creates a magnetic field in the transformer core. This magnetic field induces a current in the secondary winding depending on the turns ratio of the transformer.
The resulting secondary current is a reduced version of the primary current, allowing safe measurement and monitoring.
Current transformers are generally designed with a magnetic core which helps concentrate and enhance the magnetic flux generated by the primary current. Core material can vary, with common options including silicon steel or ferrite. The primary winding often consists of only a single turn or even a conductor passing through the CT.
The secondary winding has several turns of wire wound around the core, creating a proportional current based on the turns ratio between the primary and secondary windings.
Types of current transformers include:
- Wound type CT: They have a primary winding wound around the core and are used in high current applications.
- Bar-type CT: The conductor acts as the primary winding and passes through a ring-shaped core.
These are used to measure high currents without the need for separate primary windings.
- Clamp-on CT: These are designed for easy installation around an existing conductor and require no circuit disconnection. They are useful for portable measurements.
A CT (current transformer) works by lowering high currents to a lower, more manageable level. The primary current creates a magnetic field in the transformer core, which induces a proportional current in the secondary winding. The ratio between the primary and secondary windings determines how much the current is reduced.
This allows secondary current to be safely measured or used to operate monitoring and protection devices without exposing them to high primary currents.