Global and Local Dynamic Equivalents Based on Structural Archetypes for Coherency

A previous paper [1] introduced a set of structural archetypes for coherency (SAC). Each SAC represented a set of structural conditions that caused a group of generators to remain-coherent for any disturbance outside the group (DOG). The present paper extends this concept by considering combinations of the basic SAC. It may happen that a particular group of generators within a power system (PS) does not fully satisfy the conditions for any one SAC, yet by partially satisfying the conditions for two or more of the SAC, the group may still remain coherent for any DOG. Using a linear model of the PS, two such possible combinations are considered and classified as either strong or weak linear decoupling (LD). The LD conditions combined with the original SAC form a hierarchy of structural conditions that cause coherency of a group of generators. An algorithm is presented for detecting a subset of these structural conditions. Three types of equivalents, parochial, local and global, are distinguished that exploit different SAC conditions Results of applying this algorithm to the 39-Bus New England System are presented.