English title

One of the important power quality issues is voltage sag.  The voltage sag can generate many undesirable effects on electrical equipment. The major effect of voltage sag on electrical machine is torque pulsations after and during voltage sag. In this paper, using a simple theoretical analysis called stator flux trajectory method, producing manner of the torque pulsations and the impact of sag characteristics on the pulsations severity are investigated. Also, the critical characteristics that have the worst effects on machine behavior are identified. sag magnitude and duration  and initial point-on-wave are the major characteristics that can influence the motor behavior. To justify the theoretical analysis, a typical synchronous motor simulated by applying different sag types and the results compared with the theoretical analysis. The results of the simulation confirm the validity of the proposed analysis.