This set of DC Machines Multiple Choice Questions & Answers (MCQs) focuses on “Armature Reaction -1”. 1. In a DC machine, the form of. The third effect of the armature reaction mmf distorting the flux density is in a d.c. machine it can be inferred that the equivalent circuit of the machine need not. Armature reaction in DC Generator. There are two kinds of magnetic fluxes acting in DC Generator; the first one is because of the stator poles called main flux, while the second one is because of the current flowing in the armature called armature flux. Armature reaction also comes in the way of good commutation.


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Here also, the brushes are fixed at a position corresponding to its normal load and the mode of operation. Due to these limitations, this method is generally not preferred. Inter Pole The armature reaction dc generator of brush shift has led to the armature reaction dc generator of inter poles in almost all the medium and large sized DC machines.

Inter poles are long but narrow poles placed in the inter polar axis. 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.

The inter pole is designed to neutralize the armature reaction mmf in the inter polar axis.

Armature Reaction in a DC Generator

The conductor on the right-hand sides is also combining their MMF for producing the flux in the downwards direction. Hence, the conductor on both the sides combines their MMF in such a way so that their flux goes downward direction.

This happens when machines running at no load condition. Now the machine has two fluxes, i. The armature flux is produced by the current induces in the armature conductors while the armature reaction dc generator pole flux is induced because of the main field poles. When the field flux enters into the armature, they may get distorted.

The geometrical neutral axis GNA. The magnetic neutral axis MNA.

Armature reaction in DC Generator

Now, when current start flowing through the armature conductors, due to the combined action of main flux and armature flux the MNA get shifted armature reaction dc generator GNA.

In case of a generator, the M. In order to achieve sparkless commutation, the brushes should be moved along the new MNA. It demagnetizes or weakens the main flux. Armature flux is produced due to the current flowing in armature conductors.

Armature Reaction in DC Machine

Now, if we place another winding in close proximity of the armature winding and if it carries the same current but in the opposite direction as that of the armature armature reaction dc generator, then this will nullify the armature field.

Such an additional winding is called as compensating winding and it is placed on the pole faces. Compensating winding is connected in series with the armature winding in such a way that it carries the current in opposite direction. Interpoles are the small auxiliary poles placed between the main field poles.

For this reason it is desirable to incorporate a corrective system into the generator design. These are two principal armature reaction dc generator by which the effect armature reaction dc generator armature reaction is overcome.

The first method is to shift the position of the brushes so that they are in the neutral plane when the generator is producing its normal load current.