DC generator can be used as a DC motor without any constructional change and vice-a-versa. So, both can be termed as DC machines. In dc machine field magnetic flux can be produced by current-carrying field coils. And the process of production of magnetic flux in the machine is called excitation.
Excitation is of two types one is separately excitation and the other is self-excitation. Self-excitation is further classified into 3 more types series wound, shunt-wound, and compound wound. These excitation methods constitute in few types of dc machines.
There are few types of DC generators that are given below:
- Permanent magnet DC generators
- Separately excited DC generators.
- Self-excited DC generators
- Series wound
- Compound wound
Permanent magnet DC generator
In this DC generator, a field in the magnetic circuit is produced by the permanent magnet. Permanent magnet dc generators don’t generate much power. This type of generator is rarely used in industrial applications. They are generally used in small applications like dynamos in motorbikes.
Separately excited DC generator
Separately excited dc generators are those in which the armature coil is excited by any external source (battery).
Self-excited DC generator
Self-excited dc generators are those in which the armature coil is excited by the machine itself.
Self-excited dc generators are sub-divided into three more categories:
Shunt-wound dc generator
In a shunt-wound generator, the field coil is connected in parallel with the armature. As in the shunt wound dc generator, the field coil is connected in parallel with the armature it receives the full output voltage of the DC machine. It is made of a large number of turns of fine wire.
Series wound dc generator
In this machine, the field coil is connected in series with the armature. As the field coil is connected in series it carries the large armature current. It is made of thick wire of very few turns.
Compound wound dc generator
In the compound wound generator, both the shunt and the series windings are present. If only the shunt winding is present in parallel to the armature in the machine, it is known as the short-shunt compound. If only the series winding is present in parallel to the armature, it is known as a long-shunt compound generator.
Fig. on the left is a diagram of the short shunt dc generator and fig. on the right is the diagram of the long shunt dc generator.
In a compound wound generator if the flux produced by these series fields adds the flux produced by the shunt field then the machine is called a cumulatively compounded dc generator. An when the flux produced by the series field opposes the shunt field flux then the machine is called a differentially compounded dc generator.