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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So it rotates with same rpm and as a result getting the same induced emf [1] [2] [3]. The armature’s role is twofold.

Armature (electrical)

Direction of load current equivalent flux in this direction which is shown in Fig. Inter Pole The limitation of brush shift has led reactoin the use of inter poles in almost all the medium and large sized DC machines. Thus as the load increases the armature reaction losses increases and hence the efficiency of the Generator decreases.

They have the polarity of succeeding pole coming next in sequence of rotation in generator action and proceeding which has passed behind in rotation sequence pole in motor action.

As armature reaction effects are not good for normal operation of DC Machine both generator and motor. By means of the brushes and magnetic field is produced around the conductor. Subscribe to the Newsletter: Alternator Electric generator Inchworm motor.

Timeline of the electric motor Ball bearing motor Barlow’s wheel Lynch motor Mendocino motor Mouse mill motor. The armature reaction simply shows the effect of armature field on the main field. Consequently, the coil under this tip may develop induced voltage high enough to cause a flash over between the associated adjacent commutator segments particularly, because this coil is physically close to the commutation zone at the brushes where the air temperature might be already high due to commutation process.


The direction of current on the left sides of the armature conductor goes into the paper represented by the cross inside the circle. The tip of the pole from where the armature conductors come into influence is called leading tip and the other tip opposite in direction to it will be the trailing tip. The following figure shows: Compensating Winding Commutation problem is not the only problem in DC machines.

So at this new point it avoids the circulating current and also decreases the sparking. Here also, the brushes are fixed at a position corresponding to its normal load and the mode of operation. This mutual action of armature flux on the main field flux is known as armature reaction. The cross magnetizing armature reaction effect is mainly caused by armature conductors which are located under the pole arc.

Armature Reaction in DC Machine

These windings are connected in series with the armature winding in such a position that the current flowing in the compensation winding is exactly opposite to the current flowing in the armature winding at the same time. This flash over may spread to the neighboring commutator segments, leading ultimately to a complete fire over the commutator d.c.mchines from brush to brush.

Now two small armaturee are placed in between the north-south poles known as commutated poles.

The field this comes out as the induced voltage. And the negative terminal brush is connected to winding which is wound over There are many problems like high circulating current, poor this small pole and it is connected to negative terminal.

C machine shaft energy coming from mechanical conductor is placed in magnetic field and let the current domain goes into the magnetic domain, and then finally flowing through it as shown in figure This may again cause a similar fire as described above. What is Leading and Trailing Pole tip? Now upper field is acting like a rubber band, so it is trying to push the conductor in downward direction as shown in Fig.


This can be easily understand from the load characteristics of DC Generator, which is shown below. By using this site, you agree to the Terms of Use and Privacy Policy.

This armature flux weakens and distort the main flux, thus the overall effective flux in DC Generator decrease.

The magnetic axis means the centre line between the north and south pole.

Armature Reaction in DC machines |

The resultant flux induces in the generator are shifted towards the direction of the rotation of generator. So this amplitude keeps varying then the resultant could be in any direction depending upon the amount of load current as shown in Fig. Now in neutral zone which supposed to be as zero field zone where no induced voltage coil can exist, so no current flow though the armature conductors.

Then the only flux that would exist is armwture north-south pole flux reaftion this would still the orthogonal plane and would still into the neutral zone.

Due to cross magnetization, the magnetic neutral axis on load, shifts along the direction of rotation in DC generator and opposite to the direction of rotation in DC motor. Thus, no sparking takes place. Consider, no current is flowing in the armature conductors and only the field winding is energized as shown in the first figure of the above image.