Types of DC Generator

The DC Generators are classified according to the way their field windings are connected and excited.

(A) Separately excited Generator

(B) Self excited Generator : There are two types of self excited generator

           Shunt Generator

           Series Generator

           Compound Generator

           (1) Differential compound Generator

           (2) Cumulatively compound Generator

Separately Excited Generator

• It is generator in which the field winding is energized by external DC current.

Self Excited Generator

• It is generator in which the field winding is energized by current produced by the generator itself. 
• The field winding is in series / parallel / combination of series and parallel with the armature winding.

Shunt Generator

• The field winding is connected in parallel with the armature winding in this type of DC generator. 
• Its resistance must be high because the field winding is connected parallel with the supply voltage V. 
• The field winding is made of thin wire and it consists of many turns in order to achieve high resistance. 
• The terminal voltage is less than the induced emf due to voltage drop in armature winding. Now

       I_L = V / R_L and  I_sh = V / R_sh

       I_a = I_L + I_se

      And V = E – I_aR_a 

 

Series Generator

• The field winding is connected is in series with the armature winding in the series generator. 
• The resistance of the series field winding must be low as the current passes through it. 
• The field winding is made of thick wire and it consists of few turns in order to keep low resistance. 
• The voltage drop across field winding is due to small field winding resistance. 
• As the field winding and load resistance is in series I_se = I_L  
• The terminal voltage of the series generator is reduced by voltage drop in the armature and field winding.

         V = E – I_a ( R_a + R_se )

Compound Generator

• The field poles in the compound generator are excited by both series field winding and shunt field winding. 

Cumulative Compound Generator

• The series field winding is connected such that the flux produces due to series field aids shunt field flux therefore the net flux increases as load current increases in the cumulative compound generator.

        F = F_sh +F_se

Differential Compound generator

• The series field winding is connected such that flux produced due to series field opposes shunt field flux in the differential compound generator therefore the net flux slightly decreases as load current increases.

        F = F_sh – F_se

Long Shunt Generator

• The series combination of armature and series field winding is connected with shunt field winding in the long shunt generator as shown in the Figure F.

       I_sh = V / R_sh

       I_L = V / R_L

       I_a = I_se = I_sh + I_L and

       Induced emf E = V + I_a ( R_a + R_se ) + Brush drop 

Short shunt generator

• The parallel combination of armature and field winding is connected in series with the series field winding in the short shunt generator.

       I_sh = V_a / R_sh

      V = E – I_aR_a

      I_a = I_sh + I_L

     Induced emf E = V + I_aR_a + I_seR_se + Brush drop

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