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
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
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
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
- due to armature reaction, main flux become weak
- position of MNA will get changed
- it is tough to find exact position of MNA
- improper position of MNA will lead towards sparking
- 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
- Armature reaction,
- effects of armature reaction
- 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
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