CLARIFICATIONS OF THE BCU METHOD FOR TRANSIENT STABILITY ANALYSIS

Energy function methods have been studied for many years, and have bee n applied to practical power system stability analysis problems of mul ti-machine power systems. Recent developments in real-time power syste m monitoring suggest that dynamic events can be monitored at the power system control centers, and naturally the energy function methods wer e tried as real-time stability prediction tools. However, a number of instances were uncovered, where the energy function methods which use the Potential Energy Boundary Surface as an approximation of the stabi lity boundary produce unreliable results. In particular, during severa l transient stability studies, the Boundary Controlling Unstable (BCU) Equilibrium Point method seemed to predict stable swings, whereas in reality the swings turned out to be unstable. This paper presents thes e counter-examples, and suggests an explanation as to why these method s produce a wrong result. It is hoped that this paper will lead to fur ther researches and improvements in the theory of energy function base d methods of stability analysis. In the mean time, alternative methods for the real-time stability prediction problems are under investigati on.