## Features of the DC generator

In all types of generators, the field windings, the armature windings and the external load circuit are connected in series, as shown in the figure below.

Therefore, the same current flows through the armature winding, the field winding and the load.
Let, I a = I sc = I large
Here I a = armature current
sc = current field field
There are generally three most important characteristics of a DC generator that show the relationship between different quantities, such as series field current or excitation current, generated voltage, terminal voltage and load current.

## Magnetic or Open Circuit Characteristic of DC Series Wound Generator

The curve showing the relationship between the no-load voltage and the magnetic field or magnetic or open circular curve is displayed. As they are not charging, the load terminals are open and there will be no field current in the field as the armature, field and load are connected in series and these three make a closed circuit loop. Thus, this curve can be practically achieved to separate the field winding and excite the DC generator from an external source.

Here in the diagram below the AB curve shows the magnetic characteristic of the DC generator. The linearity of the curve will continue until the poles are saturated. After this, there will be no other significant change in the DC generator terminal voltage to increase the field current. Due to the residual magnetism, there will be a small initial tendency along with the reinforcement and therefore the curve started from a point A which is a little above the origin O.

## Internal feature of DC series wound generator

the internal characteristic of the curve gives the relationship between the voltage produced in the armature and the load current. This curve is obtained by subtracting the drop due to the diamagnetic effect of the reinforcement reaction from the no-load voltage. Thus, the actual voltage produced (E sol ) will be less than the voltage without load (E 0 ). This is why the curve falls slightly from the typical open circuit curve. Here in the diagram below the OC curve shows the internal characteristic or the total characteristic of the DC generator.

## External feature of the DC generator

The external characteristic curve shows the change in the terminal voltage (V) with the load current (I large ). The voltage of the terminal of this generator type was obtained by removing the ohmic drop due to the armature resistance (R a ) and the series field resistance (R sc ) from the actual output voltage (E sol ).
Terminal voltage V = E sol – I (R a + R sc )
The external characteristic curve is below the internal characteristic curve because the value of the terminal voltage is less than the output voltage. Here in the figure, the OD curve shows the external characteristic of the DC generator.