I hope you have come across or have known about DC Generator in our previous article. If you have not seen or read it yet, read it here:
This article will elaborately explain to you the types of DC generators, which is also classified in the above article.
The magnetic field in a d.c. generator is normally produced by electromagnets
rather than permanent magnets. Generators are generally classified according to
their methods of field excitation. On this basis, d.c. generators are divided into
the following two classes:
(i) Separately excited d.c. generators
(ii) Self-excited d.c. generator
The behavior of a d.c. generator on load depends upon the method of field
excitation adopted.
1. Separately Excited D.C. Generators
A d.c. generator whose field magnet winding is supplied from an independent external d.c. source (e.g., a battery, etc.) is called a separately excited generator. The figure above shows the connections of a separately excited generator. The voltage output depends upon the speed of rotation of the armature and the field current (Eg = Pf ZN/60 A). The greater the speed and field current, the greater the generated e.m.f. It may be noted that separately excited d.c. generators are rarely used in practice. The d.c. generators are normally of the self-excited type.
2. Self-Excited D.C. Generators
A d.c. generator whose field magnet winding is supplied current from the output
of the generator itself is called a self-excited generator. There are three types of
self-excited generators depending upon the manner in which the field winding is
connected to the armature, namely;
(i) Series generator;
(ii) Shunt generator;
(iii) Compound generator
(i) DC Series generator
In a series-wound generator, the field winding is connected in series with armature winding so that the whole armature current flows through the field winding as well as the load. The Figure above shows the connections of a series-wound generator. Since the field winding carries the whole load current, it has a few turns of thick wire having low resistance. Series generators are rarely used except for special purposes e.g., as boosters.
(ii) Shunt generator
In a shunt generator, the field winding is connected in parallel with the armature
winding so that the terminal voltage of the generator is applied across it. The shunt
field winding has many turns of fine wire having high resistance. Therefore,
only a part of the armature current flows through shunt field winding and the rest
flows through the load. The figure above shows the connections of a shunt-wound
generator.
(iii) Compound generator
In a compound-wound generator, there are two sets of field windings on each pole—one is in series and the other in parallel with the armature. A compound wound generator may be:(a) Short Shunt in which only shunt field winding is in parallel with the armature winding [See Fig. (i)]. (b) Long Shunt in which shunt field winding is in parallel with both series field and armature winding [See Fig. (ii)].
References: Principles of Electrical Machine by V.K MEHTA
