Utility Experience With Coherency-Based Dynamic Equivalents Of Very Large Systems

The method of calculating dynamic equivalents of power systems by means of generator coherency has been around for some time [1,2,3] and a number of results have been described [4,5,6]. The work described in this paper utilizes some of the production grade tools which have been developed and extends previous work in several areas. Most notably, the full and reduced systems have been compared by detailed transient stability simulations of a size believed to never have been previously attempted in the power systems industry. In addition, various aspects of coherency based reduction have been studied, including the effects of detailed representation of synchronous machines within the equivalent itself. Finally, coherency-based equivalents are compared with dynamic equivalents developed by other mre traditional methods.