PREDICTING UNSTABLE MODES IN POWER-SYSTEMS - THEORY AND COMPUTATIONS

Prediction of the (critical) unstable mode of a power system due to a fault cleared immediately after the critical clearing time is useful, for example, in transient stability analysis and in relay setting. How ever, the existing methods of predicting (critical) unstable modes wer e derived mostly on heuristics and simulations. And these methods were derived for the classical power system model. In this paper, theoreti cal results for predicting unstable modes for general power system mod els are presented. It is shown that the unstable manifold of the contr olling u.e.p. (instead of the coordinate of the controlling u.e.p.) de termines the unstable mode. It is also shown that the unstable modes d ue to different fault-on trajectories with the same type-one controlli ng u.e.p. are the same. A computational scheme is developed to predict unstable modes for general power system models. To confirm the theore tical results developed in this paper, the scheme has been tested on a 50-generator, 145-bus system with promising results. Also, one applic ation of the unstable mode predictions to transient stability analysis is illustrated.