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GATE 2022 EE – Question 35

Electrical Machines · Three-phase induction machines: principle of operation, types, performance, torque-speed characteristics, no-load and blocked-rotor tests, equivalent circuit, starting and speed control · 1 mark · Numerical answer

The frequencies of the stator and rotor currents flowing in a three-phase 8-pole induction motor are 40 Hz and 1 Hz, respectively. The motor speed, in rpm, is ________. (round off to nearest integer)

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Correct answer: 585

Explanation

The slip is $s=\frac{f_r}{f_s}=\frac{1}{40}$. The synchronous speed is $N_s=\frac{120\times40}{8}=600$ rpm, so $N=N_s(1-s)=600\times\frac{39}{40}=585$ rpm.