How To Understand Current Transformers?

A current transformer (CT) - also known as a current sensing transformer or current sensor - is an instrument designed and manufactured to sense electrical current and convert it into a form more suitable for different applications. They perform these detections and conversions by measuring a larger current value in the primary winding and generating a corresponding smaller current in the secondary winding.

CTs can be classified into three categories based on how accurately they detect current within a specific range: high accuracy, medium accuracy, and low accuracy. Since each is suitable for different current sensing and/or control applications, it is important to ensure that the transformer selected for the application is suitable for the accuracy requirements. Otherwise, you may overpay for your system or underperform the system. This is why transformers are often designed with specific applications in mind.

turns ratio

The turns ratio (also called the turns ratio) is the ratio of the number of turns in the secondary winding to the number of turns in the primary winding and vice versa. This ratio is the same as the voltage ratio. For example, if the turns ratio is 1:2 (secondary to primary), the voltage in the secondary winding will be 1 volt, if the voltage in the primary winding is 2 volts.

Excitation current

Magnetizing current is the amount of current required to generate and maintain a magnetic field within the transformer core. When voltage is applied to the terminals of the transformer and the secondary circuit is open, current flows into the primary.

Core

The core of a current transformer can be made of many laminated or sintered materials. Each material exhibits different properties that make it suitable for different current sensing and conversion applications. The two most commonly used are powder (ferrite) materials (for high-frequency applications) and nanocrystalline materials (for low-frequency applications).