Question

A 60-Hz 3-phase induction motor is required to drive a load at approximately 850 rpm. How many poles should the motor have

Answer 1

Answer:

8 poles

Explanation:

Given

$Frequency, f = 60Hz$

$Speed, n_s = 850rpm$

Required

Calculate the number of poles the motor should have?

To solve this question, we make use of synchronous angular velocity  formula

$n_s = \frac{120f}{P}$

Where

$P = Number\ of\ Poles$

Substitute values for $n_s$ and f in $n_s = \frac{120f}{P}$

$850 = \frac{120 * 60}{P}$

$850 = \frac{7200}{P}$

Multiply both sides by P

$P * 850 = \frac{7200}{P} * P$

$P * 850 = 7200$

Divide both sides by 850

$\frac{P * 850}{850} = \frac{7200}{850}$

$P = \frac{7200}{850}$

$P = 8.47058823529$

However, the number of poles must be an integer.

So:

$P = 8$