Synchronous motors contain multiphase AC electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current. The rotor with permanent magnets or electromagnets turns in step with the stator field at the same rate and delta servo motor catalog pdf a result, provides the second synchronized rotating magnet field of any AC motor. A synchronous motor is only considered doubly fed if it is supplied with independently excited multiphase AC electromagnets on both the rotor and stator.
The synchronous motor and induction motor are the most widely used types of AC motor. The difference between the two types is that the synchronous motor rotates at a rate locked to the line frequency. The synchronous motor does not rely on current induction to produce the rotor’s magnetic field.
By contrast, the induction motor requires “slip”, the rotor must rotate slightly slower than the AC current alternations, to induce current in the rotor winding. Synchronous motors are available in sub-fractional self-excited sizes to high-horsepower industrial sizes. In the fractional horsepower range, most synchronous motors are used where precise constant speed is required. These machines are commonly used in analog electric clocks, timers and other devices where correct time is required.
In high-horsepower industrial sizes, the synchronous motor provides two important functions. First, it is a highly efficient means of converting AC energy to work. Second, it can operate at leading or unity power factor and thereby provide power-factor correction. Synchronous motors fall under the more general category of synchronous machines which also includes the synchronous generator.