Correct Answer - Option 4 : Under-compound
For satisfactory parallel operation of dc series generators and over the compound generator, it is necessary to connect the armatures of the two machines through a heavy copper bar, called the equalizing bar.
An equalizer bar has a low resistance conductor wire, which connects together the points in the armature winding which should be at the same potentials.
Under-compound DC generator does not need equalizers for satisfactory parallel operation.
The functions of the equalizer bus are:
- To cause the circulating current to flow within the armature winding itself, without letting them pass through the brushes.
- To avoid unequal distribution of current at the brushes thereby helping to get sparkles commutation.
- To save the brushes from handling the circulating currents.
- To reduce the magnetic flux unbalance that cause the potential difference in various parallel paths.