Effects of Power System Models on Angle Stability Margin in Transient Stability Analysis

Abstract

Transient stability is the study of synchronism when a power system is subjected to a severe disturbance such as a short circuit fault. This study involves determining the rotor angles of the machines in a power system before, during and after a disturbance through dynamic simulations. Various power system instabilities that had occurred in the past could be linked to the use of too simplified model of power system for stability assessments. The accuracy of rotor angle dynamic responses determines how well transient stability of a multi-machine power system can be examined in dynamic security assessment. This accuracy is predetermined by the model of the power system used in dynamic simulations because the rotor angle stability margin can be compromised by using a simplified model for dynamic assessment. In this work, a more detailed model of synchronous machine, two-axis model, was used and compared with classical model which is popularly used for power system transient stability studies. Differential and Algebraic Equations (DAE) model of a multi-machine power system derived using two-axis and classical models of synchronous machines were used; with machine control dynamics (excitation and governor) added for both models. These equations were solved in MATLAB and taking a full advantage of time-domain simulation. IEEE 30-Bus test system was used for the analysis to compare the rotor angle responses for two-axis model with responses obtained for classical model. The stability margin of the system was found compromised with the use of the classical model, while the two-axis model gave a response that is more dependable for dynamic security assessment.