A technique to reduce electric power system models for dynamic investigations using generator coherency

When performing transient stability simulations or studies to examine the dynamic frequency behavior of large electric transmission systems, a detailed dynamic model of the system is used to evaluate the time domain behavior after specific events (e.g. short circuits or fast load changes). When dealing with large power systems with a large number of synchronous generators, the simulation durations even on up-to-date computers quickly approach several hours or days. Therefore, it is desirable to investigate the behavior of such a system using a less complex simulation model while still obtaining sufficiently precise simulation results. In this paper, a step-by-step procedure to reduce a given power system model for dynamic investigations using generator coherency is shown. It leads to a less complex model and, thus, to shorter simulation durations. The steps of the procedure are exemplarily presented by reducing the IEEE 39 bus system for a short circuit and discussing the deviations that are to be expected compared to the original power system model.