The three-phase synchronous motor is a unique and specialized China Pulley electric motor. As the name suggests, this motor runs at a constant quickness from no load to full load in synchronism with line frequency. As in squirrel-cage induction motors, the acceleration of a synchronous electric motor is determined by the amount of pairs of poles and the line 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 certainly 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 will 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 engine, which requires slip in order to produce torque.
Synchronous motors are not self-starting and therefore require a method of bringing the rotor up to close to synchro nous speed prior to the rotor DC power can be used. Synchronous motors typically start as a normal squirrel cage induction motor through use of particular rotor amortisseur windings. Also, there are two fundamental methods of offering excitation current to the rotor. One technique is by using an external DC resource with current provided to the windings through slip rings. The other method is to really have the exciter installed on the common shaft of the electric motor. This arrangement does not require the usage of slip bands and brushes.
An electrical system’s lagging power factor could be corrected by overexciting the rotor of a synchronous engine operating within the same system. This will create a leading power factor, canceling out the lagging power element of the inductive loads. An underexcited DC field will create a lagging power element and because of this is seldom utilized. When the field is normally excited, the synchronous electric motor will run at a unity power factor. Three-phase synchronous motors can be used for power element correction while at the same time performing a major function, such as operating 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” means of con trolling power factor. It does the same job as a financial institution of static capacitors. Such a machine is called a synchronous condenser or capacitor.