I am editing a table of motors.

I am looking for the correct terms to distinguish two types of motors: motors whose speed is less than the AC frequency (all inductions / squirrel cage motors) from motors whose speed is completely independent of the AC frequency (universal motors and repulsion motors).

Normally, the former is called "asynchronous" thought they are "quasi-synchronous".

What about the latter? They are too "asynchronous" but they are completely asynchronous.


Please understand, electrically and magnetically

  • synchronous machine and brushed DC machine are twins
  • asynchronous machine and transformer are twins

(The repulsion motor is a special sort of asynchronous machine. The brushless DC motor is a special sort of synchronous machine.)

So your categories make very little sense. That's why there isn't a term for it.

In case you wonder, the brushed DC machine is synchronous to its own speed, that's what the commutator is for. Because it's always synchronous, you can feed any frequency to it, given that the field current is in phase with the rotor current. In an universal motor, that's ensured by putting the field and rotor winding in series.


Well, you are trying to state a difference in "asynchronous" versus "quasi-synchronous", but I think that's not really valid; "a"... = not, "quasi..." = partly or almost, which would fall under "not" as well. But I see your other point IF you are defining AC motors as being frequency dependent or not, because your unknown class (universal and repulsion) although still "not" synchronous as well, get there in a different way.

I vote for "synchronous", "asynchronous", and "unfettered" AC motors. Unfettered meaning their speed is not tied to the AC source.

  • \$\begingroup\$ > unfettered ... I like that. \$\endgroup\$ – Davide Andrea Sep 14 at 1:54
  • 1
    \$\begingroup\$ To be honest, it was the result of a peek at the thesaurus... \$\endgroup\$ – JRaef Sep 16 at 18:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.