Overview of power system stability concepts

Since power systems rely on synchronous machines for the generation of electrical power, a necessary condition for the transmission and exchange of power is that all generators rotate in synchronism. The concept of power system stability relates to the ability of generators on a system to maintain synchronism and the tendency to return to and remain at a steady state-operation point following a system disturbance. This presentation begins with a discussion of the generator as a source feeding a very large remote system (the "single-machine infinite-bus" representation), to introduce the concepts of generator internal voltage and angle difference between the generator and infinite bus. Simple relationships are developed for the analysis of classical steady state stability, transient and dynamic stability. The latter two modes of oscillation are the primary focus of modern security limit studies.