Correct Answer - Option 3 : reduce sparking at brushes
The common causes of brush sparking in the universal motor (AC series motor) are:
- Open armature winding
- Shorted armature winding
- Shorted field winding
- High commutator mica
- Brushes are not in a properly working state
Compensating winding in AC series motor is used to reduce sparking of brushes.
Important Point:
In a DC machine, two kinds of magnetic fluxes are present (armature flux and main field flux). The effect of armature flux on the main field flux is called as armature reaction.
The effect of armature reaction can be reduced by following methods
a) By using compensating winding
b) By using commutation poles or inter-poles
c) By reducing the cross section of pole pieces
