Armature reaction in DC Machines?
Armature reaction is the effect of the magnetic flux produced by the armature current on the main field flux in a DC machine¹.
The armature reaction changes the distribution of the magnetic field, which affects the operation of the machine³.There are two main effects of armature reaction:-
**Demagnetization effect**: The armature flux weakens the main field flux, reducing the generated voltage in a DC generator or increasing the back emf in a DC motor¹⁴.-
**Cross magnetization effect**: The armature flux distorts the main field flux, shifting the position of the magnetic neutral axis (MNA) from the geometrical neutral axis (GNA)¹². The MNA is the axis along which no emf is generated in the armature conductors as they move parallel to the flux lines². The brushes should be placed on the MNA to avoid sparking and commutation problems¹².To reduce the armature reaction, some methods are:-
**Compensating winding**: A winding placed in slots on the pole faces that carries the same current but in opposite direction as the armature current, canceling out the armature flux².-
**Interpoles**: Small auxiliary poles placed between the main poles that produce a flux opposite to the cross magnetization effect, restoring the MNA to its original position².