The Yoke provides shape to the dc machine. It provides mechanical support to the poles. It also provides a low reluctance path for the magnetic flux. The Yoke is usually constructed of cast iron or steel.
The Poles produce the magnetic flux from the field current. The pole consists of windings made of copper which are wound on to a core made of cast iron. The field winding is connected in series or parallel to the the main winding.
3. The Pole Shoe
The Pole shoe is an extension of the pole. The pole shoe acts as a "lens" to the magnetic flux and helps spread the flux uniformly over the armature.
4. The armature Core
The armature core is made of Electrical Steel. It function of the core is to hold the armature windings in slots. It also serves as a path for the magnetic flux through the machine. The core is made of laminations to prevent eddies.
5. The Commutator
The commutator helps collect the emf built in the core windings. The commutator consists of copper segments which are insulated from each other. Mica is usually used for insulation. The segments of the commutator are connected to the coils of the armature.
The Brushes in a dc machine are made of carbon. Carbon has the property of self-lubrication. The carbon is usually sintered with copper to provide better conductivity. The brushes are spring loaded so that they have better contact with the commutator surface. The brushes serve to collect the emf generated in the machine. The brushes slide over the commutator such that the current direction is always in the same direction. Thus a pulsating direct current is obtained from the alternating voltage of the armature core.
The windings carry the current in the dc machine. The windings are made of copper and are placed in slots in the core. The windings are wound as a wave winding or a lap winding depending on the current the windings will carry.