Chapter 31, Problem 1SQ

Excluding slip, at what speed (r/min) will an eight-pole, 60-hertz, 240-volt motor run?

To determine

Calculate the speed in rpm for of an eight pole, $240\text{V}$, $60\text{-hertz}$ squirrel cage induction motor.

Answer to Problem 1SQ

The speed in rpm of a squirrel cage induction motor is $900\text{rpm}$.

Explanation of Solution

Given data:

The number of poles $\left(n\right)$ is $8$.

The frequency $\left(f\right)$ is $60\text{Hz}$.

The line voltage $\left(E\right)$ is $240\text{V}$.

Formula Used:

Write the expression to calculate the speed in rpm of a squirrel cage induction motor.

$\text{Speed}\text{in}\text{rpm}\text{=}\frac{\text{60×Hertz}}{\text{Pairs}\text{of}\text{poles}}$ (1)

Calculation:

The total number of poles in the motor is $8$. Therefore, the number of pairs of poles of the motor is $4$.

Substitute $60$ for $\text{Hertz}$ and $4$ for $\text{Pairs}\text{of}\text{poles}$ in Equation (1) to find speed.

$\begin{array}{c}\text{Speed}\text{in}\text{rpm}\text{=}\frac{\text{60×60}}{4}\\ =\frac{3600}{4}\\ =900\text{rpm}\end{array}$

Conclusion:

Thus, the speed in rpm of a squirrel cage induction motor is $900\text{rpm}$.