DC Generator and DC Motor↗ have same general construction. The structure of dc machine consists of two basic parts termed as stator and rotor. Constructional parts of dc generator↗ are explained as follows:
Stator is the stationary part of dc generator. The main function of stator in dc generator is to provide main magnetic flux in which the armature coil rotates. It consists of field winding, poles and pole shoes.
Field winding applies to that winding which produces main magnetic flux in a machine. In case of dc generator, field winding is applied to the stator within which the armature rotates. Field coils consists of number of salient poles↗. Field windings are wound on a poles in such a way that whenever electric current passes through it, they act like electromagnet↗.
Poles of dc generator acts like an electromagnet. Field windings are placed on the poles to produce required magnetic flux. Filed poles are generally laminated in order to reduce eddy current losses↗.
Pole shoe is used to spread the magnetic flux in the air gap uniformly and to support the field windings.
Rotor is the basic part of dc generator. It consists of armature core, armature windings and commutator. Dc generator rotor is also called armature.
Armature is the rotating part of dc generator and it is cylindrical in shape. It consists of core which is laminated in order to reduce eddy current losses. Core slots are used to hold armature windings.
Armature windings are placed in the slots provided on the armature core (can be seen in the above fig). They are in close circuit winding form having a multiple turns of copper wire. When armature rotates, emf is induced in the armature windings. Coil ends of armature winding is connected to the commutator segments.
Commutator is a mechanical rectifier used for obtaining a rectified waveform at the output in order to get dc voltage. It converts the alternating voltage produced in the armature winding into unidirectional (dc voltage) voltage across the brushes. Commutator is made up of commutator segments which are insulated from each other. It it is mounted on the shaft of dc machine.
Brushes of dc generator are usually made up of carbon or graphite. They have a good electrical conductivity and made up of soft materials so that they will not scratch the commutator surface segments. When the shaft of dc generator rotates, commutator segments are placed in such a way that brushes comes in contact with the surface of those segments. Hence brushes takes unidirectional current from commutator to the external circuit. Actually the purpose of brushes in dc generator is to make electrical connection between commutator and external load circuit.
Commutation poles (also known as interpoles) are similar to the main field poles placed in the interpolar region between the main poles. They are connected in series with armature winding through brushes. The main purpose of using commutating poles is to neutralize the armature reaction in dc generator↗ in order to improve commutation.
Shaft is the rotating part of dc generator which is used to transfer mechanical energy to the machine. Armature of dc generator is mounted over the shaft.
Yoke is the outer covering of dc generator. For small dc machines, it is made up of cast iron while in case of large dc machines, it is generally made up of steel. The main function of yoke is to provide mechanical support to the internal parts of machine. It also provides path to the magnetic flux produced by the poles.