What is meant by armature reaction? Explain how compensating winding and interpoles are used tominimize the effect of armature reaction

Armature reaction refers to the effect on the magnetic field in the air gap of a DC machine due to the magnetic field set up by the armature current. The armature magnetic field has two effects: it weakens the main field (demagnetizing effect) and it distorts the main field (cross magnetizing effect).

Compensating windings and interpoles are used to minimize the effect of armature reaction in the following ways:

1. Compensating Windings: These are series windings embedded in the main pole faces opposite the armature conductors. They carry the armature current and produce a magnetic field that opposes the armature field. This reduces the demagnetizing effect and the distortion of the main field.

2. Interpoles: These are small poles placed between the main poles and carry a winding connected in series with the armature. The magnetic field produced by the interpole winding is in the same direction as the main field in the vicinity of the interpoles. This helps to neutralize the cross magnetizing effect of the armature reaction at the commutation zone, reducing sparking at the brushes.

In summary, both compensating windings and interpoles are used to counteract the effects of armature reaction, ensuring a more uniform magnetic field and better performance of the DC machine.