An analysis of mechanisms of voltage instability

Analyzing mechanisms of voltage instability is necessary for an understanding of the physical phenomenon and a development of control actions. The author reviews some analytical properties of voltage instability as related to tap-changing operations, load dynamics, and generator excitation limits. The analytical results are related to the physical role of each mechanism and the combined effect in a voltage collapse event. This information is valuable in helping one to understand not only how a dynamic phenomenon develops but also the type of corrective control actions needed. The concept of voltage recovery region which can be used to guide control actions is also reviewed. This concept is then explored further for a system model which incorporates the effect of active power and frequency