Static voltage stability analysis of power systems considering induction motor components of loads

For static voltage stability studies of a power system, the loading of the system is increased incrementally and slowly (in certain direction) to the point of voltage collapse. The MW-distance to this point is a good measure of system voltage stability limit. The voltage profile of the system is shown by the PV-curves which are plotted using continuation power flow programs as the loading varies from the base values to the point of collapse. Most reported studies consider constant PQ (or at best constant impedance, constant current, constant power, called ZIP) models for loads. Given, in average, 60% of the loads include induction motors which do not follow the ZIP-model, the results obtained from these PV-curves may be erroneous. In this paper, voltage stability analysis is performed through continuation power flow program that accommodates the model for the induction motor components of the loads. The method is tested using the New England 39-bus Power System. Comparison of the presented method with the commonly used method shows that the voltage stability limits found commonly can be too optimistic. It was found that when induction motor components of the loads are considered, the obtained voltage stability limit is smaller and the overall voltage profile of the system is very much different than that found using only PQ-load models.