The rotor resistance and standstill reactance per phase of a 3-phase slip-ring induction motor are 0.5 Ω and 1 Ω respectively. What should be the value of external resistance per phase to be inserted in the rotor circuit to give maximum torque at starting?
1
1 Ω
2
0.5 Ω
3
0.05 Ω
4
2 Ω