The flux and the magnetization current in the CT core is characterized by a nonlinearity relationship. For AC system, each time the magnetic field is reversed, a small amount of energy is lost to hysteresis in the magnetic core.
However, for most current transformer operating in the lower region, the flux and the magnetization current can be approximated to a linear relationship.
There is a theory for providing some sort of explanation about some issues arose by the magnetic materials. It is assumed that each ferromagnetic material has particular magnetic dipole domains (Bloch domains), the same way the chemistry claims about any molecule. These Bloch domains, in the absence of an external magnetic field, are oriented according to the orientation given by the usual attraction-repulsion forces that govern at that level.
When an external magnetic field is applied, the Bloch domains are forced to orient themselves to the direction given by that external magnetic field. To make this happen, the magnetic field has to have enough ‘strength’ to beat the attraction-repulsion forces existing in the natural status of the material. The stronger the field (magnetic field intensity H), the easier to follow the new orientation for the Bloch domains. This explains somehow the non-linearity of the B-vs-H characteristic.
