Effect of voltage sag duration on the air-gap magnetic flux patterns and peak electromagnetic torques in saturated synchronous motors

In this paper, the effect of voltage sag duration on the analysis of the air-gap magnetic flux patterns and the largest post-sag peak electromagnetic torques in saturated synchronous motors is studied. Moreover, the effect of the saturation both in the direct and quadrature axes and of the cross-magnetizing phenomenon (the magnetic coupling between the direct and quadrature axes) on the magnetic flux patterns and post-sag peak electromagnetic torques is investigated. An analysis of the air-gap magnetic flux patterns and the largest post-sag peak electromagnetic torques is presented as affected by: (1) the sag duration, (2) the different saturation modellings, (3) the sudden phase shift of the air-gap magnetic flux just after the end of the sag, and (4) the change in the rotor speed (rate of change of the load angle) specially in the cases of relatively long sag durations.