A 440 V, 25 hp, 4-pole, Y-connected three-phase wound-rotor induction motor has the following circuit parameters:
R1 = 0.46 02, R2 = 0.33 0, x1 = 1.10, X2 = 0.46 02, and Xm = 250. (stator referred)
Rotational losses (including core loss) = 500 W (constant).
(1) At a slip of 0.04, use the complete equivalent circuit model to calculate:
(a) Motor speed
(b) Stator current
(c) Input power factor
(d) Efficiency
(2) Use the simplified Thevenin's equivalent circuit to calculate:
(a) The developed maximum torque
(b) The speed at which the maximum torque is developed.
(c) The starting current
(d) The starting torque
(3) If an external resistance equal to the rotor resistance is added to the rotor circuit, then
calculate:
(a) The developed maximum torque
(b) The speed at which the maximum torque is developed.
(c) The starting current
(d) The starting torque
(4) If the supply frequency is reduced to 50 %, calculate the stator current, the developed air-gap
torque, and the maximum torque at a slip Of 0.04.
(5) If the supply frequency is reduced to 50 %, calculate the stator current, the developed air-gap
torque, and the maximum torque at a slip of 0.04.
(6) If the terminal voltage and supply frequency are simultaneously reduced to 50%, calculate the
stator current, the developed air-gap torque, and the maximum torque at a slip of 0.04.
