Electrical machines are categorized into two..

There are two types of motor.

AC motor.
DC motor.
There are two kinds of three phase motor.

Synchronous motor.
Asynchronous motor.
The essential difference between asynchronous and synchronous motor , slip presents in asynchronous electric motor .At running condition slip of an asynchronous motor lies from 0 to 1 1. . In asynchronous engine both starting and working torque is required. Asynchronous motor has moderate starting torque . Asynchronous motor is usually a single fed electric motor.In asynchronous electric motor field is stationary armature rotates .

Three phase synchronous machines have a stationary three phase armature and a wound rotor. They are of two types:

synchronous generator or Alternator: Main workhorse of the energy 2Q==generation industry; they are rotated 12v Motor mechanically by a prime mover at synchronous rate and it creates three phase electricity. Image of PMA used in cars:
2. Synchronous motor: They are continuous speed three phase devices capable of working at synchronous swiftness. They are mostly found in constant quickness mechanical drives. They are more efficient in comparison to induction motors.
A synchronous machine has derived its name from the idea that the rotor will rotate in synchronicity with the rotating magnetic field.

Simply speaking, for a 2 Pole machine (electric motor) the rotating magnetic field rotates at 3000 rpm; the rotor of synchronous machine also rotates at the same quickness i.electronic. 3000 rpm. That is achieved through special constructional features in production this types of machines. There is no slip in synchronous machines like regular induction motors.

Normally three phase supply is available commercially and the design is also meant for the same. This is why ‘three phase’ is added with synchronous machine name.