Function of an interpole in a DC machine
An interpole in a DC machine is a small auxiliary pole placed between the main poles to reduce the harmful effects of armature reaction and improve the overall performance of the machine. The primary function of interpoles is to eliminate or neutralize the armature reaction, thus preventing excessive sparking at the brushes and ensuring better commutation.
When the current in the armature conductors creates magnetic fields, these fields can interact with the main pole flux, causing distortions in the overall magnetic field within the machine. This distortion, known as armature reaction, can lead to excessive sparking between the brushes and commutator segments, damaging these components and decreasing the overall efficiency and lifespan of the DC machine.
To counteract this armature reaction, interpoles (also known as commutating poles or auxiliary poles) are placed in between the main field poles. These interpoles are usually connected in series with the armature winding and carry the same current as the armature.
When the armature current flows through the interpole winding, it generates a magnetic field that is in the same direction as the armature's magnetic field, thus neutralizing the harmful effect of armature reaction. This results in a more uniform magnetic field across the air gap, reducing sparking and ensuring smooth commutation.
In summary, the primary function of interpoles in a DC machine is to improve commutation and overall performance by minimizing the effects of armature reaction and maintaining a more uniform magnetic field within the machine.