Question

A 220, 8 pole, 50 Hz, 3-phase star connected, wound rotor induction motor has a rotor impedance of $(0.02+j0.08)\Omega /\text{phase}$ at standstill and has negligible stator impedance. The maximum torque developed by the motor is _______N-m.

• A. 3850.51

Answer 1

The correct option is A 3850.51
$\text{The slip at maximum torque is,}$

$S_{maxT}=\frac{R_2}{X_2}=\frac{0.02}{0.08}=0.25$

$\text{Synchronous speed,}$

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

${\omega }_s=\frac{2\pi }{60}\times N_s=\frac{2\pi }{60}\times 750$

$=78.54rad/sec$

$\text{Stator voltage,}$ $V_1=\frac{220}{\sqrt{3}}=127V$

$\text{Maximum torque developed by the motor,}$

$T_{max}=\frac{3V_1^2}{2{\omega }_s\times X_2}=\frac{3\times (127{)}^2}{2\times 78.54\times 0.08}$

$=3850.01N-m$