Load Model for Stability Studies

A transient stability study of a cogeneration petrochemical power system is presented. Detailed load models were employed, and the effect on the stability was analyzed. The newly developed stability program created by the Energy Systems Research Center contains the following features which are not found in conventional stability programs: IEEE Standard STI, ST2, ACI excitation models; speed-governing systems for gas turbines which include the effects of temperature; rectifier load dynamic model; a robust subroutine of the fourth-order Runge-Kutta method to solve differential equations for fast solution; and dedication capacity with continuous program execution under islanded condition. There is always a debate about the cutoff frequency between the cogeneration producer and the connecting utility during system emergency. The authors feel this newly developed program with its detailed representation of load models, governor models, and excitation models, offers more accurate results than the conventional stability programs available today for this type of study. This program also offers efficient and accurate studies of an industrial power system. A sample study is included in this paper.