Question 6.1: Determine the number of poles, the slip, and the frequency o...
Determine the number of poles, the slip, and the frequency of the rotor currents at rated load for three-phase, induction motors rated at:
A. 2200 V, 60 Hz, 588 r/min.
B. 120V, 600 Hz, 873 r/min.
We use P = 120f/n, to obtain P, using nr, the rotor speed given to obtain the slip.
A.
P=\frac{120\times 60}{588} =12.245But P should be an even number. Therefore, take P = 12. Hence
n_{s}=\frac{120f}{P} =\frac{120\times 60}{12} =600 r/minThe slip is thus given by
s=\frac{n_{s}-n_{r} }{n_{s} } =\frac{600-588}{600} =0.02The rotor frequency is
f_{r} =sf_{s}=0.02\times 60=1.2 HzB.
P=\frac{120\times 600}{873} =82.47Take P = 82.
n_{s}=\frac{120\times 600}{82} = 878.05 r/min
s=0.006
f_{r}=0.006\times 600=3.6 Hz
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