Protection Engineering Basics and Schemes Protection Engineering | Page 11
I P is primary current
N p is primary number of turns N s is secondary number of turns R i is internal resistance and L m is magnetization Inductance I s is secondary current L s is secondary impedance or leakage reactance R s is CT secondary resistance Vs is secondary or output voltage I m is magnetization current I e is excitation current Do not be confused with separate magnetization and excitation current , because vector sum of internal resistance and inductive reactance is magnetization impedance
Z = R i + jX Lm Since X Lm = 2 ∗ pi ∗ f ∗ L m
Also note thatX Lm ≫ > R i , that is why some time in some schematics drawings only X Lm is mention . Also L s is much small so that it can be neglected .
1.1.2 Burden : Burden is the load of any current transformer ; it measured in unit ofohm , but mention in Voltage Ampere