The synchronous motor is a three-phase motor whose magnetic field is generated in the rotor via an excitation winding or permanent magnets. Synchronous motors have better efficiency and lower moments of inertia (see Moment of gyration) than asynchronous motors for the same rated torque. They do not have slip, but a load-dependent angular difference between the rotor position and the rotary field of the supply voltage.
Synchronous motors are used in industrial applications, e. g. as servo motors, in the power range up to approximately 10 kW. They are are not self-starting.