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Abstract
Voltage sags are short duration reductions in RMS voltage, caused by short circuits, overloads, and starting of large motors. This thesis studies the effect of voltage sag on the induction machine performance. The induction machine torque depends on the square of f the applied voltage. Hence, any voltage reduction will massively affect the machine !, performance. The thesis studies the power quality problems and gives its different classes f with simple definitions and associated figures. It also gives the definition of voltage sag ~.
and the factors affecting its characteristics. A brief literature review for most important
I subjects that handle voltage sag problems is also presented. The thesis also includes a review on some voltage sag mitigation techniques and describes its advantages, disadvantages, structures, and their theories of operation. Moreover, the thesis presents the mathematical phasor type model for three-phase induction machine. Based on this model, a simulation study is carried out to investigate the effect of voltage sag on induction motors. The simulation study is done for two different power ratings, namely, 20hp and 50hp power ratings. The simulation results focus on the machine performance during fault and the machine recovery after the fault is cleared. The study includes the effect of induction motor parameters, such as rotor resistance, inductance and motor inertia, on the machine performance during voltage sag. Finally, the transformer, feeding the motor, connection (vector group) on the voltage sag is an important factor that is considered and simulated for different transformer connections. The simulation study considers voltage sag characteristic and how it is affected by machine parameters and rating. Moreover, the effect of transformer connection on the voltage across each phase during voltage sag under unbalanced fault conditions is introduced. General conclusions have been given at the end of the thesis.