Power Transformer Protection Using a Multiregion Adaptive Differential Relay

This paper presents a new adaptive approach to improve the performance of the power transformer differential relay. The proposed approach distinguishes internal faults and disturbances based on the differential current trajectory and adopted weighting factors depending on the differential current locus in the relay characteristic. The traditional dual-slope differential characteristic is divided into three operating regions with the corresponding weighting factors. Two other control regions, that is, inrush and current-transformer (CT) saturation detection regions are utilized to avoid maloperation of the proposed relay in the case of inrush and CT saturation conditions. Meanwhile, a combination of phase differential units is introduced as a new technique to decrease relay operation time. The proposed relay rapidly detects all studied internal faults, while it is stable during transformer energization and CT saturation due to external faults. A real 230/63-kV power transformer is simulated using PSCAD/EMTDC for evaluating the performance of the proposed relay. Extensive simulation studies show that the proposed approach results in a faster and smarter differential protection scheme.