In an induction motor, the current that produces the rotor’s magnetic field is induced by the movement of the rotor conductors through the stator’s magnetic field. The rotor conductors move through the stator magnetic field because the rotor speed is less than the speed of the stator magnetic field by an amount called slip. Synchronous means “happening, existing, or arising at precisely the same time” or “recurring or operating at exactly the same periods.” In a synchronous motor, each revolution of the rotor corresponds to exactly one revolution of the stator’s magnetic field. The synchronous motor is named for the exact, turn-for-turn, matching of the speed of the rotor to the speed of the stator magnetic field. The principal of the induction motor requires a difference between these two speeds. There are other important differences between induction motors and synchronous motors. There are also different types of induction motors and different types of synchronous motors. However, it is the difference or lack of difference between the rotor speed and the speed of the stator’s magnetic field that is the defining difference between induction motors and synchronous motors.
