Question
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)
Answer :
585 (Range : 580 to 590)
(i) 3-∅ Induction motor
(ii) Pole, P = 8
(iii) Rotor current frequency, fr=1Hz
(iv)Stator current frequency, fs= 40 Hz
Motor speed, Nr (in rpm)
Rotor current frequency,fr= sfs
Slip, = fr/fs = 1/40
Synchronous speed Ns = (120 × fs)/P= (120 × 40)/8 = 600 rpm
Motor speed, Nr = (1 - s)Ns= 585 rpm
Hence, the correct answer is 585 rpm.
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