Question

What is slip in an induction motor?

Answer 1

Slip in an induction motor refers to the difference between the speed of the rotating magnetic field (synchronous speed) and the actual speed of the rotor. It is expressed as a percentage of the synchronous speed and indicates how much slower the rotor is moving compared to the magnetic field.

Here's a simple breakdown:

1. Synchronous Speed: This is the speed at which the magnetic field produced by the stator (the stationary part of the motor) rotates. It depends on the frequency of the supply current and the number of poles in the motor.
   

  

1. Rotor Speed: This is the actual speed at which the rotor (the rotating part of the motor) spins.
   

In an ideal scenario (no slip), the rotor would spin at the same speed as the synchronous speed, but that doesn't happen in real-world induction motors. The rotor always moves a bit slower than the synchronous speed because of the way the motor works — there needs to be a relative motion between the magnetic field and the rotor to induce current and produce torque.

Formula for Slip:

The slip \( S \) is calculated as:

\[
S = \frac{N_s - N_r}{N_s} \times 100
\]

Where:

1. \( S \) = Slip (in percentage)
   

1. \( N_s \) = Synchronous speed (in rpm)
   

1. \( N_r \) = Rotor speed (in rpm)
   

Key Points:

1. At full load, the slip is usually small, typically 1-6%.
   

1. At no load, the slip is very low, close to zero.
   

1. At start-up, the slip is 100% because the rotor is stationary, and the speed difference is maximum.
   

The slip is important because it tells us how efficiently the motor is running. A higher slip means the motor is not running as efficiently and may indicate issues like overloads or mechanical problems.