Real-Time Stability Assessment based on Synchrophasors

In this paper, an overview is provided of a new method that in real-time provides an early warning for an emerging blackout that are characterized by a slowly increasing angular separation between sub-groups of system generators. Such angular separation between subgroups of generators can eventually cause in very sharp decline in system voltages at intermediate locations between the two groups as the angular separation approaches 180 degree. In order to receive an early warning for the occurrence of such type of blackouts, the boundaries of the system generators aperiodic small-signal stability are suggested to be monitored. For that purpose, method for real-time assessment of aperiodic small-signal rotor angle stability is presented. The approach is based on an element-wise assessment of individual synchronous machines where the aim is to determine the maximum steady state power that each synchronous generator can inject into the system. The limits for maximum injectable power represent the boundary for aperiodic small signal stability. The concept of the proposed method is tested on two different systems. The results show that the method is capable of accurately detecting when a given machine crosses the stability boundary. The method can as well provide in real-time a margin to the machines stability boundary, which can be used as an early warning for an impending system stability problem.