A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted. The maximum torque equal to twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit. The slip at the full load torque will be?

Correct Answer: 2.7%
Tfl/Tem = 2/((sm/sf)+ (sf/sm)) 1/2 = 2/((0.1/sf)+(sf/0.1)) s^2-0.4s+0.01=0 s=0.0268.