Types of DC Generators

Classification of DC Generators

DC Generators are classified based on the method in which the field winding is excited. The following provides the classification of the various types of DC generators.

diagrammatic representation showing the various types of DC generators 

Basically the DC generators are classified into two types.

1. Separately excited generators and

2. Self-excited generators.

Separately generator Generators:

In separately excited DC machines the necessary magnetic flux is provided by field winding which is energized by an external DC source. The field winding is usually connected to a battery. The field current and field flux is independent of the armature circuit current.

Self-excited Generator:

Self-excited generators use their own generated current to energise the field winding to provide the field flux. Though there is no flux produced by the field coils at the time of starting the generator as there will be no current, the initial flux is provided by residual magnetism present in the machine. There are three types of self-excited generators which differ from each other in the manner in which the field winding is connected.

1. Shunt generator

2. Series generator

3. Compound generator

Shunt generator
(goto DC Shunt Generator for full article)

In shunt generator the field winding is connected in parallel to the armature conductors making the voltage across the field is equal to the full voltage generated by the generator but carry less current.

Series generator

(goto DC Series generator for full article) 

The field winding is placed in series with the armature conductors in a series generator. The field as in series with the armature, it has to carry full load current. So they are made of very less turns and thick conductors. These generators are used as boosters for voltage.

Compound generators:

The compound generators have two field windings instead of a single field. It consists of both the series winding and shunt windings. These are of two types

1. Long shunt and

2. short shunt

In a long shunt DC machine the shunt winding is connected in parallel with the series combination of both the armature and series windings. Whereas in short shunt machine the shunt winding is connected in parallel only with the armature and this parallel combination of armature and shunt field is in series with the series field winding.

The compound generators are further classified into two based on the way of magnetic fields produced by the shunt and series windings. They are,

1. Cumulative compound and

2. Differential compound

If the series field aids the shunt field then the generator is said to be cumulatively compounded whereas if the series field opposes the shunt field then it is said to be differentially compounded machine.