Induction motor behavior due to symmetrical and un-symmetrical faults

Abstract

This paper presents induction motor behavior caused by symmetrical and unsymmetrical faults. PSCAD/EMTD power system simulation was used for a simple model and the investigation purpose. Voltage sags are generally caused by faults on transmission and distribution systems. The voltage produced may be either symmetrical or unsymmetrical, depend on type of the faults. Symmetrical fault is faults due to three-phase short circuit and causes balanced sag. Unsymmetrical fault is faults caused by single-line to ground, phase to phase and two-phase faults and result in unbalanced sags. When the voltage sags occur at terminal of an induction motor, the consequences are speed loss, current and torque peaks may appear at beginning of the fault and voltage recovery instants. Symmetrical fault result in more severe voltage sag than unsymmetrical fault. These are indicated in the large current peak, speed sharply drop, toque drops is deeper. Generally transient current and transient torque appear at the beginning and the end of faults instant.