A case study on REF low impedance IED mal operation

A New Simple Method to Avoid Maloperation of Transformer Restricted Earth Fault Relay during External Fault Events

“…The restricted earth fault (REF) protection scheme is designed to respond to such earth faults [2]. But, current transformer (CT) saturation caused by either the magnetizing inrush currents or severe external faults may make the REF relay *Corresponding Author Institutional Email: mehdi.hosseini@nit.ac.ir (S. M. Hosseini) maloperate [3][4][5]. It should be noted that the strictly CT dimensioning can improve the protection system immunity against CT saturation; however, the issue is not solved completely [6].…”