Key Considerations for Current Tranformers

Note: CT's provide an isolated, accurate measurement of the current in the primary. 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
• Dielectirc / 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.