Performance of restricted earth fault protection scheme in the presence of current transformer remanence

In modern power system protection, an accurate transformation of primary short circuit current is vital to ensure correct operation of the high impedance Restricted Earth Fault (REF) protection scheme used for transformer protection. The dc component in the fault current as well as the remanent flux cans causes severe saturation conditions if the current transformer is not selected correctly. Behavior of the current transformer during the transient condition is important as this will determine the stability of the REF protection scheme. This paper discusses how the remanence phenomenon beside the dc component in the fault current can causes severe saturation to the current transformer and affects the stability of the REF protection scheme.