What is armature reaction? What are its effects on a loaded generator? How can these be eliminated?

Armature reaction:

When current flows in the armature conductors a flux surrounds these conductors. The direction of this armature flux is such that it reduces the flux from the field poles, resulting reduction in both generated voltage and terminal voltage.

So we can say that the interaction between armature flux and field flux is called armature reaction.

Effects on a loaded generator:

When a load is connected to a generator, of course current flow exists. When current flows through a conductor a magnetic field is set up around the conductor. When several conductors are placed together, the flux from each conductor is combined to produce a resultant flux. The flux from the conductor on the left side of the armature and the flux from the conductor on the right side of the armature cause a resultant flux in the centre of the armature that is downward in direction.

There are now two fluxes inside the generator, one produced by the main field poles of the generator and the other by the current in the armature conductor. These two fluxes now combine to form a new resultant flux these new resultant flux is not in the same direction as the main field flux but runs from the tip of one of the poles across the armature to the tip of the other pole. The armature conductor are now cutting this new resultant flux that is not in the same direction as the main field flux which the conductor were originally cutting.

Since the brushes were at right angles to the main field flux, they can’t be at right angle to new resultant flux with the brushes in their present location they will be Short circuiting coils in which there is a voltage induced.

The method for reducing armature reaction:

· Compensating windings

· High reluctance pole tips

· Horizontal slots in main field pole.

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