GATE EE 2015 Set 2 — Question 60
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Electrical Machines → Three-Phase Induction Machines → Starting & Speed Control
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Question
A 220 V, 3-phase, 4-pole, 50 Hz induction motor of wound rotor type is supplied at rated voltage and frequency. The stator resistance, magnetizing reactance, and core loss are negligible. The maximum torque produced by the rotor is 225% of full load torque and it occurs at 15% slip. The actual rotor resistance is 0.03 /phase. The value of external resistance (in Ohm) which must be inserted in a rotor phase if the maximum torque is to occur at start is _________.
Correct answer
0.16 to 0.18
Solution
Given:
Let be the external resistance added to the rotor circuit per phase.Substituting the values of and :Thus, the external resistance to be inserted is .
- Rotor resistance /phase
- Slip at maximum torque
- Stator resistance is negligible.
Let be the external resistance added to the rotor circuit per phase.Substituting the values of and :Thus, the external resistance to be inserted is .
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