Waveform asymmetry of instantaneous current signal based symmetrical fault detection during power swing

This paper proposes a methodology for detection of short-circuit during power swing with easy adjustment, in order to unblock the distance relay and allow its operation. If a fault occurs during power swing, it must be immediately detected and removed. One of the major challenges in these detectors is to distinguish power swing from symmetrical fault near to the electrical center (δ = 180°), as both are balanced phenomena. This work aims to propose a detector of fault which is reliable and capable of detecting a short-circuit occurring in the moment that apparent impedance crosses near to electrical center. The methodology proposed presents as main advantages, beside the ability to identify the three-phase faults during power swing near to the electrical center up to δ ≤ 120°, to work in low sampling frequency and obtain the shortest response time compared to other techniques. In order to unblock the relay in the case of a short-circuit during power swing, the asymmetry coefficient of the current signal is calculated in a window of 1 cycle (60 Hz). If the asymmetry coefficient surpasses the predefined threshold, the relay is unblocked (reset of PSB function - Power Swing Blocking), allowing its operation. The methodology uses predefined thresholds through the analysis of signals of different power swing frequencies. In this work, the defined threshold is able to cover a great number of faults and to be tolerant to power swing frequencies lower than 6 Hz. The predefined threshold avoids the need for extensive studies on stability which estimate the behavior of power electrical system.