The three-phase China Pulley synchronous electric motor is a unique and specialized electric motor. As the name suggests, this motor operates at a constant swiftness from no load to full load in synchronism with series frequency. As in squirrel-cage induction motors, the velocity of a synchronous electric motor is determined by the number of pairs of poles and the collection frequency.
The operation of a typical three-phase synchronous motor can be summarized the following:
Three-phase AC voltage is applied to the stator windings and a rotating magnetic field is usually produced.
DC voltage is applied to the rotor winding another magnetic field can be produced.
The rotor then acts like a magnet and is attracted by the rotating stator field.
This attraction exerts a torque on the rotor and causes it to rotate at the synchronous speed of the rotating stator field.
The rotor does not require the magnetic induction from the stator field because of its excitation. As a result, the engine has zero slip when compared to induction engine, which requires slip in order to produce torque.
Synchronous motors aren’t self-starting and therefore need a approach to bringing the rotor up to near synchro nous speed prior to the rotor 
DC power is certainly applied. Synchronous motors typically start as a standard squirrel cage induction electric motor through use of special rotor amortisseur windings. Also, there are two simple methods of offering excitation current to the rotor. One technique is to use an external DC supply with current supplied to the windings through slip rings. The other method is to really have the exciter mounted on the common shaft of the electric motor. This arrangement does not require the use of slip rings and brushes.
An electrical system’s lagging power factor could be corrected by overexciting the rotor of a synchronous electric motor operating within the same system. This will produce a leading power element, canceling out the lagging power aspect of the inductive loads. An underexcited DC field will produce a lagging power element and for this reason is seldom utilized. When the field is normally excited, the synchronous motor will run at a unity power aspect. Three-stage synchronous motors can be used for power factor correction while at the same time performing a major function, such as working a compressor. If mechanical power output isn’t needed, however, or could be provided in other cost-effective ways, the synchronous machine continues to be useful as a “nonmotor” method of con trolling power aspect. It does the same work as a bank of static capacitors. This kind of a machine is called a synchronous condenser or capacitor.