a 415 v 5 kw 50 hz 4-pole 3-phase wound-rotor

Question

A 415 V, 5 kW, 50 Hz, 4-pole, 3-phase wound-rotor induction motor has the following characteristics: 

1. Stator winding resistance R₁ = 2.1 Ω,
2. Referred rotor winding resistance R'₂ = 1.8 Ω,
3. Stator leakage reactance X₁ = 2.25 Ω.
4. Referred rotor leakage reactance X'₂ = 2.25 Ω.

The magnetising current, core losses and rotating losses can be neglected for this question.   

The motor is started direct on-line from a 415 V 50 Hz three phase supply. 

(a)  Calculate the starting current.

(b)  Calculate the starting torque.

(c)  Discuss how the starting current could be limited for this wound-rotor motor. 

(d)  If the motor is running at a speed of 1450 rpm, calculate the mechanical output power.