GATE EE 2021 Set 1 — Question 55
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Electrical Machines → Three-Phase Induction Machines → Starting & Speed Control
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Question
An 8-pole, 50 Hz, three-phase, slip-ring induction motor has an effective rotor resistance of per phase. Its speed at maximum torque is 650 RPM. The additional resistance per phase that must be inserted in the rotor to achieve maximum torque at start is ______ . (Round off to 2 decimal places.) Neglect magnetizing current and stator leakage impedance. Consider equivalent circuit parameters referred to stator.
Correct answer
0.5 to 0.54
Solution
Synchronous speed RPM.
Speed at maximum torque RPM.
Slip at maximum torque .
Neglecting stator impedance, .
To achieve maximum torque at start, the slip at maximum torque must be .
.
Speed at maximum torque RPM.
Slip at maximum torque .
Neglecting stator impedance, .
To achieve maximum torque at start, the slip at maximum torque must be .
.
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