AN INVESTIGATION OF VOLTAGE INSTABILITY PROBLEMS

This paper investigates voltage stability problem based on singular perturbation theory. possible voltage instability patterns are classified into four types, that is, I, II-1, II-2S and II-2D according to mechanism causing voltage instability. Several features of each type of instability are studied as well as their analysis methods. Voltage instability tends to begin with type I and then lead to one of the remaining types. The load flow Jacobian can be an effective index to approximately assess types I and II-2S instabilities, while types II-1 and II-2D require direct non-linear analyses and eigenvalue analyses, respectively. The validity of the classification proposed here has been verified through numerical simulations and theoretical analyses which take into account dynamic characteristics of generating units, loads and tap-changing transformers.