Rotating negative-sequence phasors for blocking and unblocking the distance protection during power swings

•Setting-free approach for protection of transmission lines during power swings.•Fourier filter and symmetrical components for protection of transmission lines.•Blocking and unblocking the distance protection during power swings. When power swings occur in transmission lines, the apparent impedance seen by the distance relay can shift toward the protection zone. This may result in unwanted trips in the protection system. This study proposes novel algorithms for detecting power swings and performing power swing blocking (ANSI 68) and unblocking through fault detection during power swings. The algorithms are free of settings and apply mathematical tools employed in commercial relays, such as the Fourier filter and symmetrical components. They are based on an analytical solution originally proposed in this study that demonstrates that negative-sequence phasors present a rotating behavior during a power swing, which can be used as a fundamental principle for power swing detection. The IEEE 9-bus electrical system is implemented in Matlab/Simulink to validate the proposed algorithms. The results show that the proposed algorithms effectively achieve blocking through power swing detection and achieve unblocking through fault detection. The latter function is shown to perform better than two algorithms available in the literature.