Question

A 3-phase induction motor at rated voltage and frequency has a starting torque of 150% and a maximum torque of 200% of full load torque. Neglecting stator resistance and rotational losses, the slip at maximum torque will be

• A. 0.35
• B. 0.22
• C. 0.45
• D. 0.12

Answer 1

The correct option is C 0.45

$T_s=1.5T_f$

$T_{max}=2T_f$

$\text{For maximum torque}$, $s_{mT}=\frac{r_2}{x_2}$

$\frac{T_s}{T_{max}}=\frac{1.5T_f}{2T_f}=\frac{2s_{mT}}{1+s_{mT}^2}$

$i.e,1.5s_{mT}^2-4s_{mT}+1.5=0$

$\therefore s_{mT}=0.45$