DC machine whether it is motor or generator will have four essential parts. They are
- Field System
- Brush and Brush gear
1. Field System
The objective of field system in DC machine is to provide uniform magnetic field, within which armature rotates. For small rating motors permanent magnets are used and for large size machines electromagnets are used. Electromagnets are proffered for large machines because of the higher magnetic effect and its field strength regulation which can be achieved by controlling the magnetizing current.
Field System of a DC machine consists of magnets called as pole shoes bolted to the pole cores. Pole cores are usually of circular section and are used to carry the field current windings. Pole cores are connected to the yoke of the machine.
An armature is a rotating part of a dc machine and is built up in cylindrical section. The purpose of the armature is to rotate the conductors in the uniform magnetic field. It consists of insulated coils wound around the iron cylinder and arranged such that when cut by uniform magnetic field, it produces the electric current in the windings.
A commutator is a form of the rotating switch placed between the armature and the external circuit. It helps in reversing the flow of current direction to the external circuit at the instant when the electric current reversal takes place in the armature current. This results in the current obtained by the external circuit are always unidirectional.
The function of brushes is to collect the current from the commutator and supply it to the external load circuit. The brushes are rectangular in shape and rest on the commutator. Copper or Carbon Graphite is used for making the brushes.