Armature Reaction
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چکیده
Armature Reaction: The effect of magnetic field set up by armature current on the distribution of flux under main poles of a generator. The armature magnetic field has two effects: (i) It demagnetises or weakens the main flux and (ii) It cross-magnetises or distorts it. Fig 1 shows the flux distribution of a bipolar generator when there is no current in the armature conductors. The brushes are touching the armature conductors directly, although in practice, they touch commutator segments, it is seen that: (a) the flux is distributed symmetrically with respect to the polar axis, which is the line joining the centres of NS poles. (b) The magnetic neutral axis (M.N.A.) coincides with the geometrical neutral axis (G.N.A.). Magnetic neutral axis may be defined as the axis along which no emf is produced in the armature conductors because they move parallel to the lines of flux. Or M.N.A. is the axis which is perpendicular to the flux passing through the armature.
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