Basic Theory and Practical Considerations in a Current Transformer

In this paper, a brief discussion about the theory and the governing fundamentals of a current transformer (CT) is presented. A classical modeling of the CT identifying the essential parameters is introduced and the basic formulas relating the CT voltage, current, burden, and their relationships have been discussed. Practical procedures for measuring the various burdens connected to a typical distribution circuits are analyzed. ANSI and IEC standards regarding CT types, accuracy class, characteristics, and burdens are compared. CT saturation has been addressed and examples showing simple analyses have been provided. Dynamic characteristics of a CT for generalized transient analyses have been introduced. Concluding remarks regarding practical approximations and guiding principles have been presented.