Short Answer:

A Current Transformer (CT) is an instrument used to measure high currents by converting them into lower, manageable currents that can be read by standard meters or protective relays. It helps in safely monitoring current in power systems without directly connecting the measuring device to high-voltage circuits.

It works on the principle of electromagnetic induction, where the primary winding carries the actual current, and the secondary winding produces a proportionally reduced current. This smaller current is then used for measurement, monitoring, or protection without exposing instruments or personnel to high currents directly.

Detailed Explanation:

Current transformer 

A Current Transformer (CT) is a special type of transformer used in electrical systems to scale down high current values into smaller, proportional values. These smaller currents can be easily handled by measuring instruments like ammeters, energy meters, or relays for protection and monitoring.

CTs are essential components in power transmission, distribution, and industrial systems, where direct measurement of high current would be dangerous or impractical.

Construction and Basic Structure:

• Primary Winding: Usually consists of one or a few turns, sometimes just a conductor passing through the CT core.
• Core: Made of laminated silicon steel to minimize losses and carry magnetic flux efficiently.
• Secondary Winding: Has many turns of wire and is connected to the measuring instrument or protection device.
• Burden: The external load connected to the CT’s secondary, such as a relay or meter.

Working Principle:

The CT operates on Faraday’s Law of Electromagnetic Induction. When current flows through the primary conductor, it produces a magnetic field in the core. This field induces a current in the secondary winding.

• The secondary current is proportional to the primary current but at a lower magnitude.
• The standard secondary current is usually 5 A or 1 A, regardless of the high primary current.
• The turns ratio determines the level of current reduction. For example, a CT with a ratio of 1000:5 reduces 1000 A in the primary to 5 A in the secondary.

Important Note: The secondary winding of a CT should never be left open while the primary is energized, as it can cause high voltage across the open ends, which is dangerous.

Types of CTs:

1. Wound Type: Both primary and secondary windings are wound on the core.
2. Bar Type: A solid bar acts as the primary winding.
3. Toroidal Type: No physical primary winding; the conductor is passed through the CT core opening.

Applications of Current Transformers:

• Measurement: Connecting to ammeters, energy meters for current monitoring.
• Protection: Feeding current to protective relays in case of faults like overcurrent or short circuit.
• Metering: Accurate billing and monitoring in power systems.
• Control: Used in automatic control systems for current feedback.

Advantages:

• Allows safe and easy measurement of high current.
• Provides electrical isolation between high current circuit and measuring instruments.
• Used in both single-phase and three-phase systems.
• Compact and reliable for industrial use.

Conclusion:

A Current Transformer (CT) is a critical device in electrical engineering that enables the safe measurement and monitoring of high current by stepping it down to a lower value. It works using electromagnetic induction and plays an important role in energy metering, system protection, and control. Without CTs, handling and analyzing high-voltage systems would be unsafe and difficult.