Construction Details of Synchronous Motor


     As there in no constructional difference between dc generator and dc motor, similarly there is no difference between the construction of synchronous motor and synchronous generator ( alternator ).


     The construction of synchronous motor is basically similar to alternator of rotating magnetic field type. It consists of two main parts, stator and rotor.


Stator :


(i) It is stationary part of a machine.

(ii) The armature winding is placed on the stator and so it is called stator winding.

Construction Details of Synchronous Motor

(iii) The stator consists of a cast iron frame, which supplies the armature core ( or ) stator core having slots on its inner periphery for housing the armature conductors.

(iv) The stator core is build up to sheet steel laminations to reduce the eddy current losses.

(v) Ventilating ducts are provided in the frame for cooling the machine.

(vi) The stator winding is a 3-φ distributed winding excited by a 3-φ AC supply.


Rotor :


(i) It is a rotating part of a machine.

(ii) Rotor carries a field winding which is supplied with direct current through two slip-rings.

(iii) Rotors are two types namely : 

     1. Salient pole type ( or ) projecting pole type. 

     2. Non-salient pole type ( or ) smooth cylindrical type.

(iv) Practically most of the synchronous motors are used salient pole type construction. 

  

Salient Pole Type Rotor :


Construction Details of Synchronous Motor

(a) It have a large diameter and short axial length.  

(b) Poles are projecting out of rotor surface. 

(c) Air gap is non uniform. 

(d) The poles are laminated and carry the field winding. 

(e) The individual field pole windings are connected in series. The field winding is excited through a d.c. supply from slip rings provided on rotor.  

(f) The pole faces are usually provided with slots for damper winding ( or ) squirrel cage winding.

(g) The damper bars are short circuited at both ends by copper rings.

(h) The function of damper winding is to develop starting torque and prevents hunting in a synchronous motor.


Non-Salient Pole Type Rotor :


Construction Details of Synchronous Motor

(a) It have small diameter and very long axial length.

(b) The rotor consists of smooth solid forged steel radial cylinder having a number of slots along the outer periphery.

(c) Field windings are embedded in these slots and are connected in series to slip-rings through which they are excited by D.C. supply.

(d) Air gap is uniform.

 
     As we see in the dc machines, the field winding which is stationary is kept on the stator and the armature winding which is rotating in on the rotor. 


     But in synchronous machines, it be reversed where armature is kept stationary and the field winding will be at rotating. This type of synchronous machine construction as more advantages than dc machines type synchronous machine construction and it as limited applications.


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