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GATE 2021 IN – Question 38

Electrical Circuits and Machines · Transformers and electrical machines · 2 marks · Multiple choice

A slip-ring induction motor is started by adding resistance to the rotor circuit. Compared with a shorted rotor, the benefit is ______.

  1. Higher starting torque
  2. Lower starting power factor
  3. Higher starting current
  4. Lower starting losses

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Correct answer: (A) Higher starting torque

Explanation

At starting slip s=1, rotor torque is proportional to R2/[R2²+X2²]. Adding suitable external resistance moves the rotor toward the maximum-torque condition R2=X2, increasing starting torque while limiting current. The intended benefit is **higher starting torque, A**.