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

The operation of a typical three-phase synchronous motor could be summarized the following:
Three-phase AC voltage is applied to the stator windings and a rotating magnetic field can be produced.
DC voltage is put on the rotor winding another magnetic field is definitely produced.
The rotor then acts such as 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 for its excitation. Because of this, the engine has zero slip when compared to induction engine, which requires slip to be able to produce torque.
Synchronous motors are not self-starting and therefore need a approach to bringing the rotor up to close to synchro nous speed before the rotor DC power is used. Synchronous motors typically begin as a normal squirrel cage induction motor through use of special rotor amortisseur windings. Also, there are two fundamental methods of offering excitation current to the rotor. One method is to use an external DC source with current supplied to the windings through slide rings. The other technique is to have the exciter mounted on the normal shaft of the engine. This arrangement does not require the use of slip rings and brushes.

An electrical system’s lagging power factor can be corrected by overexciting the rotor of a synchronous motor operating within the same system. This will produce a leading power factor, canceling out the lagging power gear motor for greenhouse aspect of the inductive loads. An underexcited DC field will create a lagging power aspect and because of this is seldom utilized. When the field is generally 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 operating a compressor. If mechanical power output is not needed, however, or can be provided in other cost-effective ways, the synchronous machine remains useful as a “nonmotor” means of con trolling power factor. It can the same work as a bank of static capacitors. Such a machine is named a synchronous condenser or capacitor.