A 4-pole, 50 Hz, 3-phase induction motor has a rotor resistance of 4.5 Ω/phase and a standstill reactance of 8.5 Ω/phase. With no external resistance in the rotor circuit, the starting torque of the motor is 85 Nm.
(a) What is the rotor voltage at standstill?
(b) What would be the starting torque if 3 Ω resistance were added in each rotor phase?
(c) Neglecting stator voltage drop, what would be the induced rotor voltage and the torque at a slip of 0.03?