What are the types of DC Generator

What are the types of DC Generator

Depending on the method of excitation used .d.c generators are classified in two types .

       

     1. Separately excited generator 

     2. Self excited generator

Self excited generator classified in three types . 

     1. Shunt generator 

     2. Series generator

     3. Compound generator

Compound generator classified in two types 

     1. Long shunt compound generator

     2. Short shunt compound generator

compound generator

compound generator 

     In this type, the part of the field winding is connected in parallel with armature and part in series with the armature. Both series and shunt field winding are mounted on the same poles. Depending upon the connection of shunt and series field winding compound generator is further classified as .

       

     1. Long shunt compound generator 

     2. Short shunt compound generator 

1. Long shunt compound generator

     In this type, shunt field winding is connected across the series combination of armature and series field winding as shown in the picture.

2. Short shunt compound generator 

     In this type, shunt field winding is connected, only across the armature excluding series field winding as shown in the below picture

Series Generator

Series Generator 

     When the field winding is connected in series with the armature winding while supplying the load then the generator is called series generator. It is shown the picture.

     Field winding in this case is denoted as S1 and S2. The resistance of series field winding is very small and hence naturally it has less number of turns of thick cross-section wire as shown in the picture. Let Rse be the resistance of the series field winding.

     

Shunt Generator

Shunt Generator 

     When  the field winding is connected in parallel with the armature and the combination across the  load then the generator is called shunt generator .

     

     The field winding has large number of turns of thin wire so it has high resistances. Let Rsh be the resistance of the field winding .

Self Excited Generator

Self Excited Generator 

      When the field winding is supplied from the armature of the generator itself then it is said to be self excited generator. Now without generated e.m.f., field cannot be excited in such generator and without excitation there cannot be generated e.m.f. So one may obviously wonder, how this type of generator works. The answer to this is residual magnetism possessed by the field poles, under normal condition.

      Practically though the generator is not working, without any current through field winding, the field poles possess some magnetic flux. This is called  residual flux and the property is called residual magnetism. Thus when the generator is started due to such residual flux, it develops a small e.m.f. which now drives a small current through the field winding. This tends to increase the flux produced. This in turn increases the induced e.m.f.

This further increases the field current and the flux. The process is cumulative and continues till the generator develops rated voltage across its armature. This is voltage

building process in self excited generators.

      Based on how field winding is connected to the armature to derive its excitation, this

type is further divided into following three types.

i) Shunt generator

ii) Series generator

iii) Compound generator

Explain Separately excited generator

Separately excited generator

     When the field winding is supplied from external separate d.c supply i.e excitation of field winding is separate then the generator is called separately excited generator .

     The field winding of this types of generator has large number of turns of thin wire. So length of such winding is more with less cross-sectional area. So resistance of this field winding is high in order to limit the field current .