Question

A 8-pole, 50 Hz, 3-phase induction motor has blocked rotor reactances per phase equal to 5 times to the rotor resistance per phase. The speed at which maximum torque is developed is _____rpm.

• A. 600

Answer 1

The correct option is A 600
$\text{For maximum torque}\left(T_{max}\right)$

$s_{max,T}=\frac{R_2}{X_2}=\frac{1}{5}$

$\text{Synchronous speed,}$

$N_s=\frac{120\times 50}{8}=750$ rpm

$\text{Now at}{T}_{max}\text{speed of motor,}$

$N_r=(1-s)N_s=(1-0.2)\times 750$

$N_r=600rpm$