A 209-V, three-phase, six-pole, Y-connected induction motor has the following parameters: R1 = 0.128 Ω, R’2 = 0.0935 Ω,

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A 209-V, three-phase, six-pole, Y-connected induction motor has
the following parameters:
R1 = 0.128 Ω, R’2 = 0.0935 Ω, Xeq =0.49Ω.
The motor slip at full load is 2%. Assume that the motor load is
a fan-type. If an external resistance equal to the rotor resistance
is added to the rotor circuit, calculate the following:
a. Motor speed, Starting torque, Starting current,
and Motor efficiency (ignore rotational and core losses)
b. Calculate the value of the resistance that should be added to
the rotor circuit to reduce the speed at full load by 20%. Find the
motor efficiency.
c. If the voltage is reduced by 20%, calculate the Motor speed,
Starting torque, Starting current, and Motor
efficiency (ignore rotational and core losses)
d. If the supply frequency is reduced by 20%, calculate the
Motor speed, Starting torque, Starting current, and Motor
efficiency (ignore rotational and core losses)