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Relationships which allow to calculate the armature reaction flux at different brush configurations and different load currents are derived. Machines with brushes shifted symmetrically out of the neutral zone and the asymmetric configuration - two-speed motor - are considered. The calculated results are illustrated with characteristics which give the value of the useful flux as a function of armature current and brush shift angle. Oscillograms of the induction distribution in the gap at different currents and different brush configurations are presented. The derived relationships make it possible to determine the armature reaction flux in the machine at different spacing of brushes on the commutator and at any load current. The applied method of magnetic field analysis allows to measure the real distribution of the field in the machine's gap for an arbitrarily set armature current. The obtained quantitative results point to the necessity of taking into account the effect of the armature reaction flux in machines excited by permanent magnets when the brushes are shifted out of the neutral zone.