Effect of Small Load Fluctuations on Power System Voltage Stability Studies

The aim of this paper is to examine the relationship between small-magnitude load fluctuations and their relative intensities to the voltage collapse in a power system. Based on this examination, an indicator is derived to determine the system´s relative time to collapse at various buses. This indicator is represented by the mean first passage time of a power system which is perturbed by small load fluctuations, from the domain of attraction of its stable operating point at the incidence of the voltage collapse. This time is indicative of the often on-field reported relatively long period of uncertainty, before the voltage collapse occurs. A relatively simple power system model is used in this study because the main idea is to test the viability of the proposed indicator in system dynamics representation. Since voltage collapse is a local problem, imminent critical buses or areas within the power system will be identified by this method. Computationally, the method will provide various means for its eventual on-line implementation in a large-scale power system environment. Among the many questions that this project will answer are how the size of the region of attraction, the structure of the system dynamics, and properties of various disturbances would influence the voltage collapse indicator.