An
8
-
pole induction motor runs at
7
2
0
RPM on
5
0
Hz supply. Calculate the slip.

Question

An 
8
-
pole induction motor runs at 
7
2
0
 ﻿RPM on 
5
0
 ﻿Hz supply. Calculate the slip.

VIPSolutions · Accepted Answer

# Slip Calculation for 8-Pole Induction Motor

Given:  
- Number of poles (\P\)) = 8  
 Supply frequency ($f$) = 50 Hz  
- Rotor speed ($N$) = 720 RPM

## Step 1: Calculate Synchronous Speed ($N_s$)

The synchronous speed in RPM is given by:

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

Plug in the values:

$$
N_s = \frac{120 \times 50}{8} = \frac{600}{8} = 750\ \text{RPM}
$$

## Step 2: Calculate Slip ($s$)

Slip is defined as:

$$
s = \frac{N_s - N}{N_s}
$$

Substitute the values:

$$
s = \frac{750 - 720}{750} = \frac{30}{750} = .04
$$

## Step 3: Express Slip as Percentage

$$
\text{Slip (\%)} = s \times 100 = .04 \times 100 = 4\%
$$

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**Final Answers:**
- **Slip (fraction):** .04  
- **Slip (percentage):** 4%

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