A new approach to coherency identification in large multi-machine power system

This paper based on a new coherency identification method, which is very much simple and reliable. The new coherency identification method has the capacity to identify the coherent groups perfectly, so the nature of the machines in the reduced order system is exactly similar to those of the full system. The technique involves the electrical proximity index, inertia condition index and a power variation index under faulted condition to select the coherent group of generators. Each coherent group is replaced by a single machine using the method of dynamic equivalent construction. The number of machines in the reduced order model depends on the number of coherent groups identified in the full system. So less computer memory and time are required in solving the swing equations. The new coherency identification method was applied into a large multi-machine power system and a satisfactory result was obtained.