Sunday, 28 January 2018

Armature Reaction - An Effect Of Magnetic Field In The Electric Machines Armature!!

Armature Reaction - An Effect Of Magnetic Field In The Electric Machines Armature!! 




What is Armature Reaction In The Electrical Machine , What Is Effective The Armature Reaction To ElectricalMachine And How We Can Reduce It!!!  






By Armature Reaction is meant 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:
(1) It demagnetises or weakens the main flux and
(2) It cross-magnetises or distorts.




The first effect leads to reduce generated voltage and the second to the sparking at The Brushes.



These effect are well illustrated in figer.

  • Which show the flux distribution of a bipolar generator when there is no current in the Armature conductor. 
  • For convenience  only two poles have been considered through the following remarks apply to multipolar field as well .

  •  Morever the brushes are shown touching the armature conductor directly, although in practice, the touch commutator segment, 



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It is seen that

(a)  The flux is distributed symmetrically with respect to the polar axis which is the line joining the centers of NS poles.

(b)  The magnetic neutral axis or plane (M. N. A.)  coincides with the geometrical neutralaxis or plane(G.N.A.)



Magnetic neutral axis may be defain as the axis along which no e.m.f. is produced in the Armature conductors because they then move parallel to the lines of flux.

Or

M. N. A.  Is the axis which is perpendicular to the flux passing through the Armature.




Terms used in Armature reaction


(1) Geometrical Neutral Axis(GNA)

It is the axis midway between the opposite adjacent field poles and perlendicular to the centre lines of poles.

(2)Magnetic Neutral Axis (MNA)

MNA is the axis which perpendicular to the flux passing through the armature.
It is also define as the axis along which no emf is produce in the armature conductors.

(3)Leading Pole Tip(LPT)

It is the end of the pole which first comes in contact with armature in the direction of rotation by the armature conductors.

(4)Trailing Poles Tip(TPT)

It is the end of the pole which comes in contact later with the armature in the direction of rotation.



Some Questions Related To This Topic  :

1)The armature magnetic field has how manny effects and which???
Ans: Two
(1) It demagnetises or weakens the main flux and
(2) It cross-magnetises or distorts.

2) what is the full form of G. N. A???
Ans: geometrical neutralaxis or plane(G.N.A.)

3)define Magnetic neutral axis???
Ans: as the axis along which no e.m.f. is produced in the armature conductors because they then move parallel to the lines of flux.

4)what is Leading Pole Tip(LPT)???
Ans:It is the end of the pole which first comes in contact with armature in the direction of rotation by the armature conductors.

5) give the fullform of TPT and define TPT???
Ans:Trailing Poles Tip(TPT)
It is the end of the pole which comes in contact later with the armature in the direction of rotation.



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