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 is twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit. An external resistance is now tripled in the rotor circuit. Then the slip at which maximum torque occur for the same load torque is?(a) 0.3(b) 0.268(c) 0.03(d) 3This question was posed to me in final exam.The doubt is from Operating (or Performance) Characteristics of Induction Motors in portion Induction Machines of Electrical Machines

A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the ra

1.	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 is twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit. An external resistance is now tripled in the rotor circuit. Then the slip at which maximum torque occur for the same load torque is?(a) 0.3(b) 0.268(c) 0.03(d) 3This question was posed to me in final exam.The doubt is from Operating (or Performance) Characteristics of Induction Motors in portion Induction Machines of Electrical Machines
Answer» Correct option is (a) 0.3 Explanation: The LOAD torque is maintained constant. So, r2/smT = X; r2/x = 0.1 new VALUE of SLIP will be, 3*r2/x=0.1 smT = 0.3.

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