Coherency based dynamic equivalents for transient stability studies

The development of a coherency-based technique to form dynamic equivalents for use in transient stability studies is summarized. The resulting simplification in representing areas some distance from a disturbance will reduce the time and storage requirements necessary for transient stability studies. Potential areas of application are in planning and in operations where computational savings in transient stability studies are important. The four areas of development discussed include: techniques to determine coherent areas; a coherency-based network reduction technique; aggregation of dynamic elements--machines, exciters and prime movers; and methods of updating the equivalents during daily load fluctuations. Examples being used to test the dynamic equivalencing techniques and results obtained in preliminary studies are described.