Short Answer

DC generators are mainly classified based on how their field windings are connected. The main types are separately excited generators and self-excited generators. These types differ in the way the magnetic field is produced.

Self-excited generators are further divided into shunt, series, and compound generators. Each type has different characteristics and is used for different applications depending on voltage and load requirements.

Detailed Explanation:

Types of DC generators

Separately excited DC generator

A separately excited DC generator is one in which the field winding is supplied with current from an external source, such as a battery or another generator. In this type, the field winding is completely independent of the armature circuit.

Because the field current is controlled separately, it is easy to control the output voltage of the generator. This type provides better and more stable performance. It is mainly used in laboratories, testing purposes, and where precise control of voltage is required.

However, it requires an external power source, which makes the system more complex and costly compared to self-excited generators.

Self-excited DC generators

In self-excited DC generators, the field winding is supplied with current from the generator itself. These generators use a part of the generated voltage to energize the field winding. They are more commonly used because they do not need an external source.

Self-excited generators are further divided into three main types:

Shunt generator

In a shunt generator, the field winding is connected in parallel (shunt) with the armature winding. The field winding has many turns of thin wire and carries a small current.

The voltage across the field winding is almost equal to the terminal voltage. This type of generator provides fairly constant output voltage under varying load conditions. It is widely used for lighting and battery charging applications.

Series generator

In a series generator, the field winding is connected in series with the armature winding. The same current flows through both the armature and the field winding.

The field winding in this case has fewer turns of thick wire because it carries full load current. The output voltage of a series generator increases with an increase in load current. However, it is not commonly used for practical purposes due to poor voltage regulation.

Compound generator

A compound generator is a combination of both shunt and series generators. It has two field windings: one connected in parallel (shunt field) and the other connected in series (series field).

Compound generators are further classified into:

• Cumulatively compounded generator:
  In this type, the series field supports the shunt field. It improves the voltage with increase in load and provides better performance.
• Differentially compounded generator:
  In this type, the series field opposes the shunt field. This reduces the total magnetic field and is rarely used because of unstable operation.

Compound generators are widely used because they provide better voltage regulation compared to other types.

Importance of classification

The classification of DC generators helps in selecting the right type for a specific application. Each type has its own advantages and disadvantages.

For example, shunt generators are suitable for constant voltage applications, while compound generators are used where load varies significantly. Separately excited generators are used when precise control is needed.

Conclusion

DC generators are classified into separately excited and self-excited types. Self-excited generators include shunt, series, and compound generators. Each type has unique features and is selected based on application needs.