DC generators are classified based on their method of excitation. So on this basis there are two types of DC generators:-
Self-excited DC generator can again be classified as 1) DC Series generator 2) DC Shunt generator and 3) DC Compound generator.
1. Separately excited DC generator
As you can guess from the name itself , this dc generator has a field magnet winding which is excited using a separate voltage source (like battery). You can see the representation in the below image. The output voltage depends on the speed of rotation of armature and field current. The higher the speed of rotation and current the higher the output e.m.f
2.Self Excited DC Generator
These are generators in which the field winding is excited by the output of the generator itself. As described before – there are three types of self- excited dc generators ,they are 1) Series 2) Shunt and 3) Compound.
A series DC generator is shown below in fig. in which the armature winding is connected in series with the field winding so that the field current flows through the load as well as the field winding. Field winding is a low resistance, thick wire of few turns. Series generators are also rarely used.
A shunt DC generator is shown in figure (b), in which the field winding is wired parallel to armature winding so that the voltage across both are same. The field winding has high resistance and more number of turns so that only a part of armature current passes through field winding and the rest passes through load.
A compound generator is shown in figure below. It has two field findings namely Rsh and Rse. They are basically shunt winding (Rsh) and series winding (Rse). Compound generator is of two types – 1) Short shunt and 2) Long shunt
Short shunt:- Here the shunt field winding is wired parallel to armature and series field winding is connected in series to the load. It is shown in fig (1)
Long shunt:- Here the shunt field winding is parallel to both armature and series field winding (Rse is wired in series to the armature). It is shown in figure (2)