Armature Reaction

Before starting we need to understand basic terms associated with armature reaction. Those are

  • 1.       Geometric Neutral Axis (GNA)
  • 2.       Magnetic Neutral Axis (MNA)
  • 3.       Leading Pole Tip (LPT)
  • 4.       Trailing Pole Tip (TPT)

MNA

                MNA is defined as the axis which is perpendicular to the flux passing through the armature.

GNA
               It may be defined as the axis, which is perpendicular to stator field. 



LPT

               the pole tip which is first met during the rotation armature rotation .

while another is known by TPT










ARMATURE REACTION 

We will understand armature reaction by three case.

Case  1 :when  only field winding is excited



From the figure we can see that armature winding is not connected with supply.

Brushes are touching armature conductor directly
Here we can see that, both GNA and MNA are coincide with each other and brushes are also connected to MNA

Term, Fm is indicating the direction and magnitude of field flux






Case 2: only armature winding is fed by supply



Hence no current is passing through field winding

Direction of armature current is as per the fleming right hand rule
So near N pole, current is downward direction and near S pole, it is upward direction

Here force line could be identified by screw rule
So near N pole it became clockwise direction as current is entering in downward direction.
However, near S pole it is in anticlockwise direction

Fa denotes magnitude and direction of armature flux.

Case 3: Both Field winding and armature Winding are acting together


In the load condition effect of both the cases will act together & it’s case 3

Last case is on load condition when both armature and field windings are excited

Here it can be noticed that armature flux is no more symmetrical now.
More amount of flux density is accounted near TPT due to combain flux effects

Same as,  least flux density can be seen near LPT.

Now, New resultant flux OF can be calculated by vactorial summation of armature flux and field flux
As a result position of MNA got changed. Hence, brush position also has to be changed in order to avoid sparking.

This whole process of interacting of flux is said to be armature reaction

It may also define as effect of armature flux on main flux

Effect of armature reaction


  1. due to armature reaction, main flux become weak
  2. position of MNA will get changed
  3. it is tough to find exact position of MNA
  4. improper position of MNA will lead towards sparking
  5. due to armature reaction, commutation process become difficult.





Remedies to armature reaction


To reduce the effect, firstly we can introduce inter pole in yoke, it will eliminate the shifting of brush

In order to reduce it, compensating winding can also help.
By using high reluctance pole tips, reduction in armature flux
        and using strong main field flux, we can neutralize the armature reaction.



Summary of Armature Reaction 


  1. Armature reaction, 
  2. effects of armature reaction 
  3.  remedies to armature reaction

For more deep idea, kindly watch this video

By this video you will gain about armature reaction.

We have learned,

  • Armature reaction, 
  • Effects of armature reaction
  • Remedies to armature reaction