Types of synchronous motor

Types of synchronous machine:

Two types of rotors are used in synchronous machines; salient pole and cylindrical pole.

     1)    Salient pole: 
                    salient pole machine is also known as projecting pole rotor. This type of motor is used in low and medium speed engine driven alternators. On the circumference of the rotor, large number of salient or projecting poles are placed with fixed position. 
                  It has large diameter and short axial length compare to cylindrical synchronous motor. Poles are made up of cast irons and silicon steel and concentrated winding are placed on the poles. Poles and pole shoes are laminated to reduce eddy current loss. To prevent hunting or damp out, the damper bars are used in the poles faces. 
                        This condition may occur in case of sudden change in load condition. Damper bars are made up copper and short circuited at both ends by heavy copper rings. Maximum speed of this motor is 1500 rpm.

              This type of alternators is used in hydro power plant. So, this is also known as hydro-alternator or hydro-generators.

     
     2)      Cylindrical rotor: this motor is also known as non-salient pole motor. This type of motor is used in very high-speed turbo alternator. Rotor is cylindrical. Rotor poles are less number compare to cylindrical motor. 
                     It has only 2-4 poles. It has large axial length and small diameter compare to salient pole synchronous motor. It is made up of silicon steel and the slots are made on the circumstances of rotor to receive the field winding. The maximum speed of cylindrical rotor is 3000 rpm.

             This type of alternator is used in thermal power plant or gas plant, where high speed of turbine is used.

Application of synchronous motor:

1)      It is used in power houses and sub-stations in parallel to the bus bars to improve power factor. For this purpose, it is run without mechanical load on it and over excited.

2)      Large number of induction motors or transformers operating at lagging power factor, it is used for improving power factor.

3)      Generate electric power at power plants.

4)      Control the voltage at the end of transmission line by varying its excitation (DC supply).

5)      It is used in motor generator sets requiring constant speed.

6)    It is also used in rubber mills, textile mills, cement factories, air compressors, centrifugal pumps which requiring constant speed and Pulp beaters and grinders, steel and metal rolling mills, rock and ore crushers are generally coupled or geared to the motor.