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Question 13.20: Slip and Speed of Induction Motor An eight-pole, three-phase...

Slip and Speed of Induction Motor

An eight-pole, three-phase induction motor is supplied by a 60-Hz source. At full load, the frequency of the emf induced in the rotor is 5 Hz. Find the full-load slip and the full-load speed.

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First, calculate the synchronous speed using Equation (13.39):

N=\frac{120 \cdot f}{P}     (13.39)

N_{s}=\frac{120 \times f}{P}=\frac{120 \times 60}{8}=900 rpm

The full-load slip corresponds to:

s=\frac{f_{R}}{f}=\frac{5}{60}=0.083

Using Equation (13.41) to compute the full-load speed:

s=\frac{N_{s}-N}{N_{s}}     (13.41)

N=(1-s) N_{s}=825.3 rpm

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