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A current transformer (CT) is a device used to measure alternating current (AC) by transforming the primary current into a secondary current that is proportional to the primary current.
How Does A Current Transformer Work
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Author: Site Editor
Publish Time: 2023-07-30
Origin: Site
A current transformer (CT) is a device used to measure alternating current (AC) by transforming the primary current into a secondary current that is proportional to the primary current. Here's how it works.
Construction
A CT consists of a primary winding and a secondary winding, both wound on a common 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.
Magnetic Induction
When AC current flows through the primary winding, it creates an alternating magnetic field around the conductor. The magnetic field induces a voltage in the secondary winding according to Faraday's law of electromagnetic induction.
Turns Ratio
The turns ratio between the primary and secondary windings determines the transformation ratio of the CT. For example, if the CT has a turns ratio of 1:100 and the primary current is 100 amps, the secondary current will be 1 amp (assuming an ideal CT).
Burden
The secondary winding of the CT is designed to have low impedance, allowing it to provide a current that is accurately proportional to the primary current. This low impedance is known as the burden, which is the combined resistance and reactance seen by the secondary winding.
Accuracy Class
CTs are manufactured with different accuracy classes depending on the application requirements. The accuracy class indicates the maximum permissible error of the CT within specified conditions.
Protection and Measurement
CTs are commonly used for two purposes: protection and measurement. In protection applications, CTs are connected to protective relays that monitor the primary current and trip circuit breakers in the event of abnormal conditions such as overcurrent or short circuits. In measurement applications, CTs are connected to ammeters, wattmeters, or energy meters to measure and monitor the current flow.
It's important to note that CTs should always be installed and operated by qualified professionals to ensure proper safety and accuracy.
