Design and Performance Evaluation of a High-Impedance REF Scheme for MV/LV Transformers

This paper presents the detailed engineering study conducted to design a high-impedance restricted earth fault (REF) scheme for four 11/0.415-kV, Dyn11, and 2500-kVA power transformers in an industrial power system. Analytical calculations carried out to specify the components constituting the REF scheme and to determine the appropriate relay settings are provided. The proposed REF scheme is evaluated using reliable Alternative Transients Program-Electromagnetic Transients Program simulations. The obtained results validate the adequacy of the design and highlight the advantages of using such a protection, such as fast and reliable operation even under severe current transformer saturation conditions.