|Fig.1 A cross section of typical d.c. machine|
- It serves the purpose of outermost cover of the d.c. machine. So that the insulating materials get protected from harmful atmospheric elements like moisture, dust and various gases like SO2, acidic fumes etc.
- It provides mechanical support to the poles.
- It forms a part of the magnetic circuit. It provides a path of low reluctance for magnetic flux. The low reluctance path is important to avoid wastage of power to provide same flux. Large current and hence the power is necessary if the path has high reluctance, to produce the same flux.
|Fig. 2 Pole Structure|
- Pole core basically carries a field winding which is necessary to produce the flux.
- It directs the flux produced through air gap to armature core, to the next pole.
- Pole shoe enlarges the area of armature core to come across the flux, which is necessary to produce larger induced e.m.f. To achieve this, pole shoe has been given a particular shape.
- Armature core provides house for armature winding i.e. armature conductors.
- To provide a path of low reluctance to the magnetic flux produced by the field winding.
|Fig. 4 Single Circular lamination of Armature core|
- Generation of e.m.f takes place in the armature winding in case of generators.
- To carry the current supplied in case of d.c. motors.
- To do the useful work in the external circuit.
- To facilitate the collection of current from the armature conductors.
- To convert internally developed alternating e.m.f. to unidirectional (d.c.) e.m.f.
- To produce unidirectional torque in case of motors.
|Fig. 5 Commutator|