The speed a synchronous motor will run can be determined by the number of poles of the motor and the frequency of the electrical service using the formula:
RPM = Hz* (2 / poles) * 60
RPM = shaft rotation speed or revolutions per minute
Hz = frequency or cycles/sec
Poles = number of poles of your motor.
So, for example, if you have a 4 pole motor on 60 Hz then RPM=60*(2/4)*60=1800 rpm.
60Hz is the most common frequency in the US
50Hz is the most common frequency outside the US
|Approximate Electrical Motor Speed (rpm)|
|No. Poles||Speed with Rated Load||Synchronous Speed (no Load)|
|60 hz||50 hz||60 hz||50 hz|