The assessing cores of current transformer are attached to current coils of Ammeters, Watt meter energy unit meters, Var-Meters, and Var-Hour-Meters. The zone of work all of these relays underneath the ranked of lesser of current transformer.
The evaluating cores should have high to correct supervise of the scheme amounts correctness within alter of burden levels. In fault situation, current is awfully high and might come to twenty times the rated value; thus assessing cores should be saturate to bypass the damage of undertaking instruments.
Protection cores are designed to figure at high levels of current (at fault). The correctness of those cores could further more be less evaluation with assessing cores. The saturation levels of those cores are terribly on peak of undertaking cores. Magnetization bend of current transformer with evaluation and protection cores and completely different districts of magnetization curve are shown in the figure just below.
Note: The knee issue will be outlined because the reason at that a 10% boost flux density causes 50% boost in exciting ampere -turns.