Voltage stability evaluation using the the relation between impedances

The increasing loads, the great distances between the production and consumption centers as well as the state of the transport and distribution networks turns the electrical power system operating near its stability limit. When the system gets unstable a blackout situation may occur, which is critical to the system operator and consumers. We have recent examples in United States and Italy where the system was without power for several hours, causing serious problems in hospitals and public transportations. One of the causes of a blackout may be the voltage instability, which turns this subject widely discussed and studied. The speed of evolution of the voltage stability phenomenon allows us to analyze the problem as a static problem rather than a transitory one Kundur, P et al. (1983). This article will show one way to "measure" locally the proximity of the system to the voltage stability limit.