Answer Happy

A 209-V, three-phase, six-pole, Y-connected induction motor has the following parameters: R1 = 0.128 12, R'2 = 0.0935 , Xeq=0.492 where Xeq is equivalent total reactance of stator and rotor referred to the stator side. The motor slip at full load is 2%. Given that the motor load is a fan-type. 1) Calculate the motor speed and starting torque when the applied voltage is reduced by 20%. 2) Assume that the induction motor is operating at a low near-rated slip (less than 10%). Let the developed torque of the motor be T1. Determine the percentage change of T1 when the applied voltage is reduced by 45% from the rated value while the per-phase rotor resistance is reduced by 25% from the original value. State whether T1 is increased or decreased. Hint: For a fan-type load, T1/T2 = (N1/N2)2 where T1 and T2 are developed torques before and after the applied voltage is changed and N1 and N2 are the motor speeds before and after the voltage is changed, respectively.