Main parts of alternator are the stator and a DC field winding on the rotor.
Stator is a stationary part of machine and it is made by sheet steel lamination having slots on its inner periphery. Windings are placed in these slots and serves as the armature winding of the alternator.THESE ARMATURE windings are connected in star connection.stator core having a generally cylindrical shape.
Rotor carries a field winding which is supplied by DC current through two slip rings by a DC source.That source is called exciter. Small DC shunt or compound generator is act as exciter. Based on the rotor shape rotor is classified into two types .They are given bellow
Salient (projecting) pole type.
Non salient (cylindrical) pole type.
Salient (projecting) pole type
In this type poles are placed on a large circular steel frame which is connected to the shaft of alternator.Individual field poles are connected in series. Based on the increasing frequency number of poles are incresing.ie;when frequency of 50HZ production we use large number of poles so the rotor diameter increases.
For low and medium speed alternators salient pole type alternators are using.
Non salient (cylindrical) pole type
Here rotor is made by smooth solid forged steel radial cylinder having number of slots.The field windings are placed in these slots and these are connected in series to slip rings connected to exciter.
Based on the increasing frequency number of poles are decresing.ie;when frequency of 50HZ production we use small number of poles so the rotor diameter is small.
For high speed alternators non salient pole type alternators are using.