Advantages of stationary armature
Advantages of stationary armature:
Fig: 1 Stationary Armature Windings
The field winding of an alternator is placed on the rotor and is connected to d.c. supply through two slip rings. The 3-phase armature winding is placed on the stator. This arrangement has the following advantages:
(i) It is easier to insulate stationary winding for high voltages for which the alternators are usually designed. Ii is because they are not subjected to centrifugal forces and also extra space is available due to the stationary arrangement of the armature.
(ii) The stationary 3-phase armature can be directly connected to load without going through large, unreliable slip rings and brushes.
(iii) Only two slip rings are required for d.c. supply to the field winding on the rotor. Since the exciting current is small, the slip rings and brush gear required are of light construction.
(iv) Due to simple and robust construction of the rotor, higher speed of rotating d.c. field is possible. This increases the output obtainable from a machine of given dimensions.
(v) The output current can be led directly from fixed terminals on the stator (or armature windings) to the load circuit, without having to pass it through brush-contacts.
(vi) It is easier to insulate stationary armature winding for high a.c. voltages, which may have as high a value as 30 kV or more.
(vii) The sliding contacts i.e. slip-rings are transferred to the low-voltage, low-power d.c. field circuit which can, therefore, be easily insulated.
(viii) The armature windings can be more easily braced to prevent any deformation, which could be produced by the mechanical stresses set up as a result of short-circuit current and the high centrifugal forces brought into play.