A shunt generator is a machine whose shunt field coil is connected in parallel to the armature terminals so that the generator is self-excited. The main advantage of this compound is that it does not require an external source of pathogens.
How is self-excitation achieved?
When a shunt generator is running at full speed, a small voltage is induced in the coil due to the remaining flux at the poles. This voltage generates a small and weak excitation current IX in the shunt field. The resulting small MMF acts in the same direction as the remaining flux, causing an increase in flux per pole. The doubled flux increases E0, which increases IX, which further increases the flux, which further increases E0, and so on. This progressive increase continues until E0 reaches a maximum value determined by the sector resistance and the saturation level. Below is a schematic of a shunt generator. A shunt field is designed in such a way that it is connected to the armature winding in a shunt circuit (alternative term for parallel).
Controlling the Voltage of a Shunt Generator
The induced voltage of a shunt excited generator can be easily controlled. We vary the excitation current by simply exciting a resistor connected in series with the shunt field.
-
Armature reaction in DC generator
The equivalent circuit of a generator therefore consists of a resistor Ra which is asynchronous to the voltage E0.
The latter is the voltage generated in the rotating conductors. Terminals 1 and 2 are the external terminals of the machine armature and F1, F2 are the field winding terminals.
