Dynamic Modeling of Induction Motor loads for Transient Voltage Stability Studies

Due to the complex nature of the dynamic stability studies, and the high cost of simulating large power systems in real time, most of the voltage stability studies are limited to the static techniques. The main disadvantage of the static modeling is its inability to capture the dynamic behavior of induction motors which is a common load in the power system. This paper compares between the static and dynamic models of aggregated induction motor loads. It demonstrates that in some disturbance cases, the static load modeling fails to predict the actual response of induction motor loads. The studies show that while the static load model predicts a stable operation with both the conventional P-V curve and a P-V curve of the induction motor load at different values of machine slip, the dynamic model shows unstable operation for the same cases. Finally, the effect of the dynamic load inertia on system stability is studied. Although the inertia constant of a dynamic load is significant in studying its stability, static load model is unable to take it into consideration. Simulations will show that for similar rating motors with different inertia constant, the steady state condition varies. This exposes another deficiency in static load models of induction motors.