Abstract
Owing to the large magnitude of the inrush currents, the functionality of differential protection of power transformer may be threatened in correct discrimination between inrush and internal faults. This article enhances the functionality of differential protection through a computationally efficient method that utilizes the phase angle current signals of the current transformers (CTs). The proposed discrimination criterion (PDC) tracks the fundamental phase angle of the current signals of the CTs. While during an internal fault, the phase angles of both CTs are almost constant and in phase, during the external fault and inrush currents, the phase angles of both CTs have notable distance. On this ground, this article employs a developed Kalman filter (KF)-based phase angle estimator to measure the fundamental phase angles of the current signals of the CTs. Afterward, PDC is introduced that measures the distance between the estimated phase angles of the CT's currents. Evaluating the effectiveness of the PDC with several simulated and experimental recorded current signals reveals the PDC is able to detect internal faults even in the presence of CT saturation and also to deal with inrush and external fault currents.