A Real-Time Setting-Free Synchronous Generator Out-of-Step Protection Scheme Based on Voltage Trajectory

Publication Name

IEEE Systems Journal


This article proposes a real-time, setting-free out-of-step (OOS) protection strategy for a single synchronous generator (SG) connected to a multimachine power system. To do so, the fundamental frequency phasor of the voltage at the generator terminal is measured. It will be shown that at the point of OOS, the imaginary part of the voltage crosses the zero point and becomes negative, whereas the real part of the voltage holds a negative value. On the other hand, it will be shown that during stable power swings, the imaginary part of the voltage behaves as per an OOS event, whereas the real part of the voltage becomes positive. Therefore, this principle can be used as the criterion to detect an SG OOS. Moreover, it will be shown that the proposed principle can count the number of SG pole slip occurrences so that it can trip the generator after a certain number of pole slips. The proposed scheme is a response-based algorithm and uses only locally measured voltage at the relay location. Furthermore, the network configuration and parameters do not affect the proposed scheme. Unlike the legacy impedance-based OOS detection method, which demands rigorous offline simulation studies to determine settings, the proposed scheme does not need any setting to operate. Rigorous mathematical analyses and illustrated simulation study results are presented to substantiate the efficiency of the proposed method. The performance of the proposed scheme and the polygonal relay and concentric blinder scheme are compared through comprehensive simulation studies. The results prove that the proposed scheme can be served as an efficient method for SGs OOS protection.

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