The three-phase synchronous electric motor is a distinctive and specialized electric motor. As the name suggests, this motor operates at a constant swiftness from no load to complete load in synchronism with range frequency. As in squirrel-cage induction motors, the swiftness of a synchronous motor is determined by the amount of pairs of poles and the range frequency.

The operation of the three-phase synchronous motor could be summarized the following:
Three-stage AC voltage is applied to the stator windings and a rotating magnetic field can be produced.
DC voltage is applied to the rotor winding and a second magnetic field is certainly produced.
The rotor then acts just 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. Because of this, the electric motor has zero slip compared to the induction electric motor, which requires slip to be able to produce torque.
Synchronous motors aren’t self-starting and therefore need a method of bringing the rotor up to near synchro nous speed before the rotor DC power is applied. Synchronous motors typically start as a normal 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 have the exciter mounted on the normal shaft of the electric motor. This arrangement will not require the usage of slip rings and brushes.

A power system’s lagging power factor could be corrected by overexciting the rotor of a synchronous engine operating within the same system. This will produce a leading power element, canceling out the lagging power factor of the inductive loads. An underexcited DC field will produce a lagging power element and because of this is seldom utilized. When the field is normally excited, the synchronous motor will run at a unity power factor. Three-phase synchronous motors can be utilized for power aspect correction while at the same time carrying out a major function, such as for example working a compressor. If mechanical power output isn’t needed, however, or can be provided in other cost-effective methods, the synchronous machine remains useful as a “Low Backlash Gear Reducers nonmotor” method of con trolling power element. It does the same job as a financial institution of static capacitors. Such a machine is called a synchronous condenser or capacitor.