Transient phenomena may be initiated by a balanced or an imbalanced change in the time phase or peak value of the Alternative Current (AC) and voltages U, fed to the stator winding (e.g. by a change in the peak values of symmetric positive-, negative- phase sequence voltage components, U11 or U21, respectively). A transient phenomenon may be initiated by a sudden change in an external torque, leading to an imbalance of electromagnetic torque, a resultant acceleration, and finally, a new speed value.