Magnetic or Opencircuit Characteristic (O.C.C)
Relation between \(E_0\) and \(I_f\) at a given fixed speed
Magnetization curve for the material of the electromagnets
Shape is practically the same for all generators
Relation between \(E\) actually induces in the armature (after demagnetization effect) and \(I_a\)
Characteristics is of mainly interest to the designer
Performance characteristics or voltageregulating curve
Relation between load \(V\) and \(I\)
great importance in judging the suitability of a generator for a practical purpose
Noload Characteristics
No armature reaction generated voltage is straight line
Voltage drop \(\Delta V_{AR}\) because of armature reaction
Operating Point \(P\), intersection between generator external and load characteristics by the relation \(V_L=I_LR_L\)
\(P\) gives operating value of terminal \(V\) and \(I\)

This voltage causes \(I_f=V/R_f\) to flow in the field winding
The flux is increased by mmf produced by \(I_f\)
As a result \(E_g\) increases, which further increase \(V\)
\[E_{g}\uparrow\Rightarrow V\uparrow\Rightarrow I_{f}\uparrow\Rightarrow\Phi\uparrow\Rightarrow E_{g}\uparrow\Rightarrow V\uparrow\]

If \(\Phi_{res} = 0\) disconnect the field and apply a DC voltage to the field winding.This process is called Flashing the field.
A decrease in \(R_f\) reduces the slope of \(R_f\) line resulting in a higher voltage, and viceversa
If \(R_f\) is increased to \(R_c\), the \(R_f\) line becomes tangent to the initial part of the magnetization curve
If \(R_f\) is higher than \(R_c\), the generator fails to excite.
At \(N_c\) the \(R_f\) line becomes tangential to the magnetization curve.
Below \(N_c\) the voltage will not build up.

If \(N_{se}\) is lesser than required to be flat compounded, then the generator is called to be under compounded.
In Differential Compounded \(V_T \Downarrow\Downarrow\) with \(I_a \Uparrow\).