Protection Engineering Basics and Schemes Protection Engineering | Page 10

I primary = ( N sec

N Pri

) I secondary + I excitation

It clearly showing the primary current transformed not only in secondary current but excitation current also , our main concern is secondary current but excitation current is there , more excitation current means less secondary current which is not technically desirable . To keep magnetization or excitation current as low as possible it is common practice to use good magnetic property material for Current transformer core manufacturing , so in less magnetization current our CT will be magnetically coupled with on mounted cable / conductor .

It is schematic operational drawing of Current transformer

R P is Primary Resistance L P is primary inductance e P is primary voltage pg . 10