Question

What is a slip in AC motors?

Answer 1

Slip in AC motors refers to the difference between the speed of the rotating magnetic field in the stator (synchronous speed) and the actual speed of the rotor in an induction motor. It is usually expressed as a percentage of the synchronous speed.

### Formula for Slip:
\[
\text{Slip} = \frac{Synchronous\ Speed - Rotor\ Speed}{Synchronous\ Speed} \times 100
\]

- **Synchronous Speed** is the speed at which the magnetic field in the stator rotates. This speed depends on the supply frequency and the number of poles in the motor.
- **Rotor Speed** is the actual speed at which the rotor of the motor turns.

### Why is Slip Important?
- **Slip** is necessary for the motor to generate torque. If the rotor were to rotate at the same speed as the synchronous speed, there would be no relative motion between the magnetic field and the rotor, meaning no current would be induced in the rotor, and thus no torque.
- The slip is usually small (a few percent) in motors running at full load, and it increases when the motor is under a light load or when it's starting.

For example:
- If a motor has a synchronous speed of 1500 rpm and the rotor speed is 1450 rpm, the slip would be:
\[
\text{Slip} = \frac{1500 - 1450}{1500} \times 100 = 3.33\%
\]

In summary, slip is essential for the operation of induction motors, as it allows the motor to produce the necessary torque.