One of the most interesting phenomena that occurs in a DC Motor is armature reaction. Current flowing through the armature creates its own magnetic flux called the armature flux. The action of this armature flux on the main flux set up by the field is known as armature reaction. Let us explain this through a series of diagrams. The excitation of field winding sets up magnetic flux from North Pole to South Pole. When the current flows through the armature winding, the direction of current under one pole face is same and opposite to that of other. It can be clearly seen that the resultant armature flux strengthens the main flux on the top left and bottom right side and weakens it on the other. The resultant flux in the armature region is as shown.
