Transient stability of multimachine systems with saturable exciters

A method is described for estimating the critical clearing times for a multimachine power system. It has previously been applied in situations where each machine is represented by a constant voltage behind reactance, and is extended here to the case when automatic voltage regulators and exciters with saturation limits are modelled. The aim of the method is to eliminate the need for integration of the postfault swing equations. The analysis involves classification of the unstable singular points of the postfault swing equations and study of the small perturbation behaviour of the system near such points. Results are given for a 5-machine 14-busbar system, and the method is also applied to study the sensitivity of critical clearing times to parameter changes.