CHARACTERISTICS of DC GENERATORS (Separately Excited)

 1. No-Load Characteristics

It is the curve between Induced emf and Field current, Ea = f (If)  with speed (n) = constant
This is called as saturation curve, open-circuit characteristic, magnetization curve or no-load magnetization curve.

2. Load Characteristics
It is the curve between terminal voltage and field current, Vt = f (If)  with both 'Ia' and 'n' constant
This is called as load magnetization curve.

3. External Characteristics
It is the curve between terminal voltage and load current, Vt = f (IL) with both 'If' and 'n' constant

4. Armature Characteristics
It is the curve between field current and armature current, If = f (Ia) with both 'Vt' and 'n' constant
This is called as Regulation Curve.


Separately Excited Generator

1. No-Load Characteristics
The set-up for plotting No-Load Characteristics is shown in the above figure. By varying the field resistance we can vary the field current to change the induced emf and Armature Circuit is kept open circuited and induced voltage is measured using Voltmeter. The No-Load Characteristics is shown in the figure below:

                                  OA = Residual flux

2. Load Characteristics

After load connection, If  is varied to get full load armature current and constant speed.

3. External Characteristics

Vt = Ea - IaRa = Ea - ILRL
AB → Voltage drop due to armature reaction
BC → Voltage drop due to Ra, IaRa

4. Armature Characteristics or Regulation Curve

As Armature Current is increased, the voltage reduces due to Armature Reaction and to keep voltage constant field current must be increased,