Instantaneous positive-sequence current applied for detecting voltage sag sources

This study proposes a method for detecting voltage-sag sources, using only the measurements of line currents. Instantaneous symmetrical components are introduced for accommodating the transient nature of voltage sag events, where a magnitude and phase change in the instantaneous positive-sequence current is used as a criterion. The proposed method is compared with conventional phasor-based methods known from the literature. All the discussed methods for voltage sag source detection, both the already known and the proposed ones, were evaluated by applying extensive simulations, laboratory tests and field testing. When compared with the phasor-based methods, the proposed method showed faster response, a higher degree of confidence and superior effectiveness, especially for transient voltage sag events in networks with distributed generation and active loads.