Question

How do you calculate the synchronous speed of an AC motor?

Answer 1

The synchronous speed of an AC (alternating current) motor is calculated using the following formula:

Synchronous Speed (in RPM)
=
120
×
Frequency (in Hz)
Number of Poles
Synchronous Speed (in RPM)=
Number of Poles
120×Frequency (in Hz)
    ​


Where:

Frequency
Frequency is the frequency of the AC power supply in Hertz (Hz).
Number of Poles
Number of Poles refers to the number of magnetic poles in the motor. It is typically an even number (e.g., 2, 4, 6, etc.) since most AC motors have a balanced configuration of poles.

It's important to note that the synchronous speed represents the ideal speed at which the motor's magnetic field rotates. However, due to various factors such as load, friction, and losses, the actual speed of the motor (known as the operating speed) will be slightly lower than the synchronous speed. This difference between synchronous speed and operating speed is known as "slip."

The formula above is applicable to synchronous motors, which are designed to rotate at a constant speed that is synchronized with the frequency of the AC power supply. Induction motors, on the other hand, operate at speeds slightly below synchronous speed due to slip and are more common in industrial and commercial applications.