An adaptive distance relaying algorithm with a morphological fault detector embedded

This paper presents an adaptive distance relaying algorithm (ADRA) for transmission line protection. In ADRA, a fault detector designed based on mathematical morphology (MM) is used to determine the occurrence of a fault. The Euclidean norm of the detector output is then calculated for fault phase selection and fault type classification. With respect to a specific type of fault scenario, an instantaneous circuit model applicable to a transient fault process is constructed to determine the position of the fault. The distance between the fault position and the relay is calculated by a differential equation of the instantaneous circuit model which is resolved in a recursive manner within each sampling interval. Due to the feature of recursive calculation, the protection zone of the relay varies from a small length to large, which increases as an augment in the sample window length. ADRA is evaluated on a transmission model based on PSCAD/EMDTC, under a variety of different fault distances, fault types, fault resistances and loading angles, respectively. The simulation results show that in comparison with conventional DFT-based protection methods, by which the fault distance is calculated using phasor measurements of voltage and current signals in a fixed-length window, ADRA requires much fewer samples to achieve a same degree of the accuracy of fault distance calculation, which enables much faster tripping, and its protection zone can be extended as more samples are used.