Method and monitoring system for generator slow-coherency online identification and dynamic tracking

method and a monitoring system (8) being used as a part ofa Vlfide Area Monitoring, Protection, and Control (WAMPAC) application for determining groups ofgenerators operating synchronously in an electric power system (1). The method comprises collection of PMU (4) data, such as frequency measurements, from each of the plurality of the generators. The method may further comprise filtering with a low-pass filter, determining a generator dissimilarity parameter based on direction and strength of generator electromechanical coupling between pairs of the plurality of generators, dynamically determining the observation window length based on a predetermined threshold, discarding interfering coherency indices within the given observation window, a first-order exponential low-pass filter adaptive tracking for robust coherency estimation, and finally determining the number of groups of generators based on the generator dissimilarity parameter below a predetermined threshold.