A New Phase Angle of Superimposed Positive Sequence Current-Based Discrimination Scheme for Prevention of Maloperation of Distance Relay During Severe Stressed Conditions

This article presents a new scheme for accurate discrimination between symmetrical faults and severe stressed conditions (such as power swing, load encroachment, and voltage instability) under third zone coverage of distance relay. The proposed scheme is based on comparison of phase angle of superimposed positive sequence component of current, with a preset threshold. The threshold value is decided by performing various simulations on standard test systems along with appropriate validation through analytical analysis. The performance of the proposed scheme has been evaluated on different faults and severe stressed conditions by modeling IEEE-14 and IEEE-39 bus test systems in real-time digital simulator (RTDS/RSCAD) environment. The simulation results indicate that the presented scheme is able to distinguish symmetrical faults from severe stressed conditions effectively due to substantial change in the value of phase angle of superimposed positive sequence current. The threshold values utilized in the presented technique remains almost same for transposed/untransposed and uncompensated/compensated transmission networks. Comparative evaluation of the presented scheme with the existing scheme clearly indicates its superiority in differentiating symmetrical fault under severe stressed conditions.