A novel algorithm to identify power swing based on superimposed measurements

This paper describes a novel adaptive out-of-step detection algorithm based on dissimilar measurement approaches. Two superimposed measurements enable the algorithm to detect fast as well as slow power swings. Both methods recognize power swings right from the beginning of the swing impedance movement. The first principle is based on continuous rate-of-change measurement of the traveling swing impedance. The second method continuously monitors the speed and the shape of the swing impedance trajectory. The algorithm detects extremely high swing frequencies of up to 7 Hz and maintains functionality under single-pole open conditions, i.e. auto-reclose dead time. The associated distance relay detects all kinds of internal faults, e.g. 3-phase, 1-phase and 2-phase also in the presence of power swings. Contrary to the traditional approach, the power swing detector does not need any set points or any power system stability calculation. Thus it also contributes to simpler and setting-free relaying.