Following are three important characteristics of dc generators :
No load saturation characteristics (Eg Vs I f)
It is also called open circuit characteristics or magnetic characteristics. It gives the relationship between no load generated emf in armature Eg and field current If
At gives fixed speed.
It is just like magnetization curve for the material of the electromagnets.
Its shape is practically same for all generators whether self. Excited or separately excited.
Internal characteristics(Eg verses Ia)
It gives the relation between emf generated Eg (after reducing armature reaction drop) and armature current Ia
External characteristics (V versus IL)
It gives the relation between terminal voltage V and loads current IL. This characteristic considers both the drop, armature reaction drop and armature resistance drop on Y axis where terminal voltage is represented.