Synchronous AC Motor
The Synchronous Motor is typically an AC Motor that has its rotor spinning at the same rate as the alternating current that is being supplied to it. The rotor can also turn at a sub multiple of the current it is supplied. Slip rings or a permanent magnet supplied with current is what generates the magnetic field around the rotor. - See more at: http://www.anaheimautomation.com/manuals/forms/ac-motor-guide.php#sthash.2ZBMOIOs.dpuf