The main purpose of power swing blocking is to distinguish faults from power swings. However, the faults occur during a power swing should be detected and cleared promptly. This paper proposes an adaptive concentric power swing blocker (PSB) to overcome incapability of traditional concentric PSB in detecting symmetrical fault during power swing. Based on proposed method, two pairs of concentric characteristics are anticipated which the first one is placed in a stationary position (outer of zone3) but the position of the second pair is adjustable. In order to find the position of the second pair of characteristic, Static Phasor Estimation Error (SPEE) of current signal is utilized in this paper. The proposed method detects the abrupt change in SPEE and puts the second pair of characteristic in location of impedance trajectory correspondingly. Second concentric characteristic records travelling time of impedance trajectory between outer and inner zones and compares to threshold value to detect symmetrical fault during power swing. If recorded time is lower than threshold, three-phase fault is detected during power swing. Intensive studies have been performed and the merit of the method is demonstrated by some test signals simulations.
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