Effects of symmetrical and unsymmetrical voltage sags on induction machines

This paper analyzes the symmetrical and unsymmetrical voltage sags consequences on the induction machines behavior: current and torque peaks and speed loss. These effects depend on several variables like sag magnitude and duration, type of sag, and initial point-on-wave. A wide variety of sags has been analyzed for different magnitudes, durations, and the most severe initial point-on-wave, showing the machine sensitivity in magnitude-duration plots (sensitivity curves). The severity of the different sags types has been compared by means of the Euclidean distance between the surfaces that represent the sensitivity curves. This comparison allows sags types to be divided into several groups: in general, the most severe sags are the symmetrical ones, and the least severe are the single-phase ones. The sensitivity curves can also be represented by using the positive-sequence voltage for ordinates, giving a different sags classification.