Types of DC generator ? the purpose of a commutator in a DC generator

What is a DC generator

By using a DC generator we can generate electricity, the generator function is to convert the mechanical energy into electrical energy. DC generators are mostly used for special applications or local power generation, the operational characteristics of the DC generator is really important because most of the concepts can be applied to many other electrical machines

Field winding connection


The four brushes ride on the commutator, the positive and negative brushes are connected to A1, A2 as in the figure the brushes are placed midway under poles A magnetic path is created by joining the field poles and their ends are connected to F1 and F2 in a manner that they produce north and south poles

The purpose of a commutator in a DC generator

The current produced by the electromagnetic induction would be alternating current so in order to convert it into direct current commutator is used. the armature of the DC generator is connected to the commutator segments A commutator has two segments they are insulated from one another and forms the shaft of the machine on which it rotates. The armature conductor end is connected to each commutator segment, the commutator reverses the armature coil connection to the external circuit during that time the current induced in the armature coil reverses.

Types of DC generator

It is characterized in a way in which the field excitation is provided

Separately excited generators

It has field exciter terminals which are external DC voltage source is supplied to create separate magnetic field winding, to magnetize the generator, so the magnetic winding is excited by using an external voltage source


Self-excited field generators

This type of generators doesn’t use any external Dc source it can generate magnetic field themselves. The electromotive force which is produced by the generator is supplied to the field winding. So there is no external Dc source is used and it is necessary to connect the field winding to the armature winding

  1. Shunt generator

In this generator, the shunt field winding and the armature field winding are connected in parallel through commutator and carbon brush


  1. Series generator

In this, the field winding and the armature winding are connected in series and the field winding is directly connected to the electric load and because of that the field winding conductor needs to be sized enough to carry the load current

  1. Compound generator

In this type the magnetic field is provided with the combination of the series field winding and excitation of shunt, the shunt field has many turns of wire but it carries only small current, whereas the series field winding has few turns of heavy wire and carries the load current the series field winding is in series with the armature winding

A compound generator is classified into two types

Short shunt and long shunt

Short shunt

In this the shunt field winding is wired parallel to armature and series field winding is connected in series to the load

Long shunt

In this, the shunt field winding is parallel to both armature and series field winding