A Novel Fast Algorithm for Detecting Out-of-Step Using Equal Area Criterion

In an electric power system there is a dynamic balance between generation and load in normal operating conditions. A disturbance, such as a power system fault, a sudden change of load or a trip of a generation unit may break the balance, cause the oscillations among the generator’s rotor angles and force them to adjust to a new operating condition. Due to the inertia of the generator prime movers, the adjustment will not happen instantaneously. When the disturbance is severe, the oscillations do not damp out and lead to an unstable operating conditions called out-of-step or loss of synchronism condition. A new fast algorithm is proposed in this paper to discriminate stable and out-of-step swings effectively. This algorithm uses local voltage and current measurements to classify the stable and out-of-step swings and is very fast (about 20 cycles for frequency of 60Hz) in determining an out-of-step situation compared to that of traditional time domain methods, especially for cases with long fault duration times. This method is a type of classic equal area criterion method mapped in the time domain. Using PSCAD software the proposed algorithm is tested on a single-machine infinite bus equivalent system. Simulation results studied on an equivalent system verify validity of the proposed algorithm.