Armature Reaction is the effect of magnetic flux set up by armature current The brushes of the DC machines are always placed in this axis, and hence this axis. armature reaction mmf gets added at this tip leading to considerable amount In some small d.c. machines the brushes are shifted from the position of the mag-. Commutation problem is not the only problem in DC machines. At heavy loads, the cross magnetizing armature reaction may cause very high.

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The exact distribution of the windings and selection of the number of slots per pole of the field greatly influences the design of the machine and its performance, affecting such factors as commutation in a DC ar,ature or the waveform of an AC machine. Coils of the winding are distributed over the entire surface of the air gap, which may be the rotor or the stator of the machine. If the brushes were contacting commutator segments outside the neutral plane, they would short-circuit “live” coils and cause arcing and loss of power.

So at this new point it avoids the reactkon current and also decreases the sparking.

Fig 8 Resultant flux due to interaction between two fluxes Now the flux created by armature current is in the upward direction and the direction of north-south pole flux is right angle to this flux. Armature reaction is one of the reasons that causes generated emf in DC Generator to decrease. This effect is called as armature reaction d.c.machinfs DC machines.

Armature Reaction in a DC Generator

The brush-setting method is the most common means of correcting for armature reaction in small generators those producing approximately W or less.


The inter pole is designed to neutralize the armature reaction mmf in the inter polar axis. Similarly, the right-hand side conductors carry current, and their direction goes out of the paper shown by dots inside the circle.

In the armature, an electromotive force is created by the relative motion of the reactoin and the field. This problem is more acute while the load is decreasing in generating action and increasing in motor action as then, the induced e.

The demagnetizing mmf magneto motive force thus produced is given by: You enjoy this post: From Wikipedia, the free d.c.machknes. Inter poles are made narrower to ensure that they influence only the coil undergoing commutation and its effect does not spread to the other coils.

Armature (electrical)

Windings are held in slots in the rotor or armature covered by d.c.machinrs magnets. Why not share it? The direction of current on the left sides of the armature conductor goes into the paper represented by the cross inside the circle. Aluminum armature wiring is lighter and less expensive than copper. Field created by conductor will distort the main field.

Armature reaction also comes in the way of good commutation.

Fig 11 Commutating poles to reduced armature reaction Let the commutator which is placed and also have the brushes in the neutral zone.

Alternator Electric generator Inchworm motor. At d.c.machinws loads, the cross magnetizing armature reaction may cause very high flux density in the trailing pole tip in generator action and leading pole tip in the motor action. Leave a comment Click here to cancel reply. Copper armature wiring enhances electrical efficiencies due to its higher electrical conductivity. This can be achieved by installing commutating poles in between two consecutive main poles.

By means of the rewction and magnetic field is produced around the conductor. The field this comes out as the induced voltage. This may again cause a similar armzture as described above.


D.c.macuines most generators, the field magnet is rotating, and is part of the rotorwhile the armature is stationary, and is part of the stator. By using this site, you agree to the Terms of Use and Privacy D.c.maachines. Now, there is a current in the previous loading direction because all this add up inside the core this produce effect diagram as shown in Fig.

These are two principal methods by which the effect of armature reaction is overcome.


Now two small poles are placed in between the north-south poles known as commutated poles. The effect of armature flux on the main field flux is called as armature reaction. The brushes of a generator must be set in the neutral plane; that is, they must contact segments of the commutator that are connected to armature coils having no induced emf.

In large machines subject to heavy overloads or plugging In small motors subject to sudden reversal and high acceleration. Because of this one major problem that the brushes which were supposed to be located at in the neutral zone because in neutral zone there is no voltage induced in the coil there is no brush short circuit at the point and there is no problem there is no huge circulating current.

The armature reaction changes the distribution of the magnetic field, which affects the operation of the machine.