Shrinking stability regions and expanding voltage collapse regions of power systems

A theory of voltage collapse in power systems is developed based on three mechanisms: on-load tap-changing, load dynamics and generator excitation limiting. Under the assumption that system frequency remains unchanged, the interaction among the three mechanisms is investigated in a general interconnected network model. It is found that there exists a region in the space which corresponds to monotonic fall of system voltage (collapse region). The dynamic process of voltage collapse is characterized by the voltage trajectory falling outside a shrinking stability region and entering an expanding collapse region