Question 18.9: Slipin a Single-Phase Induction Motor Find the slip of the f...

Known Quantities: Motor operating characteristics.

Find: Forward slip, s_{f}; backward slip, s_{b}.

Schematics, Diagrams, Circuits, and Given Data: Motor operating characteristics: 115 \mathrm{~V} ; 60 \mathrm{~Hz} ; 4 poles; 1710  \mathrm{rev} / \mathrm{min}.

Analysis: We first determine the synchronous speed of the motor:

n_{s}=\frac{120 f}{p}=\frac{120 \times 60}{4}=1,800  \mathrm{rev} / \mathrm{min}

The slip in the forward direction (direction of rotation of the motor) can now be computed:

s_{f}=\frac{n_{s}-n}{n_{s}}=\frac{1,800-1,710}{1,800}=0.05=5 \%

The slip in the backward direction can be computed as follows, with reference to Figure 18.26:

s_{b}=2-s_{f}=2-0.05=1.95