Equivalent Circuit of Current Transformer

 

The equivalent circuit of a current transformer  is shown:

 

VS = secondary exciting voltage
VB = CT terminal voltage across external burden
IP = primary current, A
ZE = exciting impedance, ohm
IST = total secondary current, A (IE + IS)
RS = CT secondary winding resistance, ohm
IS = secondary load current, A
XL = leakage reactance (negligible in Class C CT), ohm
IE = exciting current, A
N = CT turns ratio
ZB = burden impedance, ohm (includes secondary devices and leads)

The secondary exciting voltage is given by:

The primary current is given by:

The ratio correction factor is given by:
 
The percent ratio error is given by: