Power systems transient stability indices: an algorithm based on equivalent clusters of coherent generators

This study presents an efficient method for estimating transient stability indices of electric power systems. It is based on equivalent network reduction techniques. The electromechanical equivalent system has been accomplished by considering clusters of coherent generators. The angular speed deviations of synchronous generators have been used as a criterion to perform the groups. The reduced order is obtained by replacing two groups of coherent generators by a single machine equivalent. With these equivalents, critical fault clearing times and security margins are calculated by using the well-known equal-area criterion. The method was compared with others, especially those based on the concepts of transient energy function. The critical fault clearing times are in agreement with and very close to those obtained by using Liapunov´s direct method or the time-domain solution of the n-machine original system. Some numerical results are presented for a 3- and 10-generator power systems. The method is an excellent tool that can be applied as a filter to identify potentially harmful contingencies and to select these to perform detailed transient stability analysis.