At unity Power factor, the effect of armature Reaction is merely to distort the main field, there is no weaking of the main field and the average flux Practically Remain the same at zero P.f. lagging, Armature Reaction is directly demagnetizing and the armature Reaction weakens the main flux. This causes a Reduction in an generated MMf. A zero P.F. leading, Armature flux is now in the same direction as the field flux and, therefore the armature Reaction strengthens the main flux. This cause an increase in the generated voltage.