Transmission system wide-area back-up protection using current phasor measurements

Zone-3 of distance relays might maloperate during stresses frequently encountered in power systems, such as power swing, load encroachment, and voltage instability. This paper proposes a new protection algorithm for discrimination between short-circuit faults and other stresses in the transmission networks. The proposed method compares the sum of currents at the predetermined buses before and after the disturbance occurrence using synchronized current phasor measurements. The faulted area and line are identified as well. The optimal placement of phasor measurement units (PMUs) is tackled using a mathematical model. One of the main advantages of the proposed algorithm is decreasing the number of required PMUs in comparison with those of existing wide-area back-up protection schemes. In virtue of its computational speed, the proposed method can be exploited as a practical back-up protection cooperating with conventional protection schemes. The extensive simulation studies carried out on the IEEE 57-bus test system verify applicability of the proposed algorithm as a reliable back-up protection scheme for lines.