Armature Reaction

A reaction in a generator where the magnetic field produced by the main field winding is superimposed by the magnetic field produced by the current carrying conductors in the armature winding, Such an effect is called Armature Reaction.

Armature Reaction

Armature Reaction produces 3 undesirable effects:

1. Shifting of the Magnetic Neutral Axis (MNA) in the direction of rotation - Although the Geometrical Magnetic Axis remains at the same place. This shift causes a spark at the carbon brushes section.

2. Weakens the magnetic strength of the Main field.

In order to tackle the undeisreable effects, there are 3 ways we can incorporate:

1. Shift the position of the carbon brushes nearer or at the shifted MNA position

2. Provide additional windings named as compensating windings

Provide additional poles named as Interpoles

Interpoles

lnterpole windings are wound on narrow-faced auxiliary pole pieces located midway between the

main poles, and are connected in series with the armature, The windings are such that an interpole has

the same polarity as the next main pole in the direction of rotation, and as the fluxes are opposite in direction

to the armature flux, they can be equalized at all load by having the requisite number of turns.

ln order to provide true correction of armature reaction, the effects produced by interpoles must be supplemented, since alone they cannot entirely eliminate all distortion occurring at the main pole faces.

Compensating Windings

Compensating windings are therefore connected in series with the interpole and armature windings, and

located In slots cut in the faces of the main pole shoes. The sides of the coils thus lie parallel with the sides of

the armature coils. The ampere turns of the winding are equal to those of the armature winding, while the flux due to it is opposite in direction to the armature flux .