Necessity of a compound generators

   In practical cases power circuits such as lighting require a constant voltage. Shunt and series generators cannot be used for such situations.Because, as load current of shunt generators increases its terminal voltage falls and as load current of series generator increases the terminal voltage also increases .

     In compound generators both series and shunt windings are placed in each field pole .The series winding so connected that flux produced by it aids the flux produced by the shunt winding. (Such generators are called Cumulatively compounded generators).So as load current increases , flux produced by series winding compensates the loss of flux due to armature reaction.Then the terminal voltage of the generator remains constant.