Current Transformer


In electrical engineering, a current transformer (CT) is used for measurement of electric currents. Current transformers, together with voltage transformers (VT) (potential transformers (PT)), are known as instrument transformers.
Current Transformer (CT) 
Current transformers are commonly used in metering and protective relays in the electrical power industry.

Design and Concept

Concept of CT
- has a primary winding, a magnetic core, and a secondary winding. The alternating current flowing in the primary produces a magnetic field in the core, which then induces a current in the secondary winding circuit. A primary objective of current transformer design is to ensure that the primary and secondary circuits are efficiently coupled, so that the secondary current bears an accurate relationship to the primary current.

CT Accuracy Factor

  • Burden 
  • Burden class/saturation class 
  • Rating factor 
  • Load 
  • External electromagnetic fields 
  • Temperature and 
  • Physical configuration. 
  • The selected tap, for multi-ratio CTs 

Application of CT
Clamp meter
- Used to measure current  


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