1 Answer
The frequency of the power supply directly affects the speed of an induction motor. Here's how:
1. Synchronous Speed:
The speed of an induction motor is determined by its synchronous speed, which depends on the frequency of the power supply and the number of poles in the motor. The formula for synchronous speed (\(N_s\)) is:
\[
N_s = \frac{120 \times f}{P}
\]
Where:
- \(N_s\) = Synchronous speed (in RPM)
- \(f\) = Frequency of the power supply (in Hz)
- \(P\) = Number of poles in the motor
Key Point: As the frequency \(f\) increases, the synchronous speed of the motor increases as well.
2. Effect of Frequency on Speed:
- If the frequency of the power supply increases, the motor’s synchronous speed increases, meaning the motor will rotate faster.
- Conversely, if the frequency decreases, the synchronous speed decreases, and the motor will rotate slower.
3. Slip and Rotor Speed:
In an induction motor, the actual rotor speed is always a little less than the synchronous speed. This difference is called slip. The rotor speed can be expressed as:
\[
N_r = N_s \times (1 - \text{Slip})
\]
The slip depends on the load applied to the motor, but the synchronous speed itself is still influenced by the frequency of the power supply.
In Summary:
So, in simple terms: Higher frequency = faster motor speed, and Lower frequency = slower motor speed.
1. Synchronous Speed:
The speed of an induction motor is determined by its synchronous speed, which depends on the frequency of the power supply and the number of poles in the motor. The formula for synchronous speed (\(N_s\)) is:\[
N_s = \frac{120 \times f}{P}
\]
Where:
- \(N_s\) = Synchronous speed (in RPM)
- \(f\) = Frequency of the power supply (in Hz)
- \(P\) = Number of poles in the motor
Key Point: As the frequency \(f\) increases, the synchronous speed of the motor increases as well.
2. Effect of Frequency on Speed:
- If the frequency of the power supply increases, the motor’s synchronous speed increases, meaning the motor will rotate faster.- Conversely, if the frequency decreases, the synchronous speed decreases, and the motor will rotate slower.
3. Slip and Rotor Speed:
In an induction motor, the actual rotor speed is always a little less than the synchronous speed. This difference is called slip. The rotor speed can be expressed as:\[
N_r = N_s \times (1 - \text{Slip})
\]
The slip depends on the load applied to the motor, but the synchronous speed itself is still influenced by the frequency of the power supply.
In Summary:
- The synchronous speed of an induction motor increases as the supply frequency increases.
- The rotor speed also increases, but it will always be slightly lower than the synchronous speed due to slip.
So, in simple terms: Higher frequency = faster motor speed, and Lower frequency = slower motor speed.