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Current Transformers Design Considerations

CT's provide an isolated, accurate measurement of the current in the primary circuit. Usually CT's have a one turn primary - a conductor that is part of the circuit being measured. CT's have very little effect on the circuit being measured, as we measure AC currents.

Variables for Consideration

  • Current Range
  • Overload current rating
  • Primary conductor opening
  • Sensitivity - volts per amp
  • Burden VA and resistance
  • Internal / external termination
  • Frequency response
  • Accuracy and linearity
  • Ambient temperature / allowable temperature rise
  • Dielectric / insulation resistance
  • Cost

Miscellaneous Comments

  • Low frequency response is limited, primarily, by magnetizing inductance.
  • High frequency response is limited, primarily, by stray winding capacitance and magnetic coupling between primary and secondary.
  • Manufacturability and cost targets have major design influence.


Current Transformer Mechanical Drawing
Current Transformer Mechanical Drawing