Study of Saturation of current transformer as one of special transformers is applicable study in power systems. Let us consider a primary current with a peak value I1p at the CT saturation limit. Let I2p be the peak value of a primary current greater than I1p , which is thus going to saturate the CT. Let I1 and I2 be the peak values of the currents at the CT secondary corresponding to I1p and I2p through the transformation ratio. I2 is the design value that would be obtained if there was no saturation phenomenon. The current curves look like those in Figure below. The magnetic induction B is proportional to ?I dt . The surface designed by the current is thus proportional to B. The current I1 being at the saturation limit, the surface S1 designed by I1 is proportional to the saturation magnetic induction. 