1. ARMATURE
REACTION
MADE BY : DEEPAK (006)
RUPESH JAIN (031)
SIDHARTH SHARMA (029)

2. Basic terminology
of a DC generator
• A Generator is a machine which converts mechanical energy
into electrical energy.

3. Stator: The stator is the fixed part of the generator that
supplies the magnetic field in which the coils rotate. It may
consist of two permanent magnets with opposite poles facing
and shaped to fit around the rotor.
Rotor: In its simplest form, the rotor is a part of generator
made to rotate within a magnetic field. In actual practice, the
armature is usually referred to as rotor.

4. WHAT
IS
ARMATURE
REACTION
????

5. ARMATURE REACTION:
All current-carrying conductors produce
magnetic fields. The magnetic field produced by
current in the armature of a DC generator
affects the flux pattern and distorts the main
field. This distortion causes a shift in the neutral
plane, which affects commutation. This change
in the neutral plane and the reaction of the
magnetic field is called ARMATURE REACTION.

6. Armature reaction can be better
understood with this figure:-

7. UNDESIRABLE EFFECTS OF
ARMATURE REACTION
1. Armature reaction causes a net reduction in the field flux per
pole. Due to this net flux decrease, induced armature e.m.f.
decreases and also the torque decreases.
2. Distortion of the main field flux along the air gap i.e. MNA
axis shifted. Due to this there is a problem of commutation
which results in copper losses, iron losses, sparking etc.

8. Methods To Reduce
Armature Reaction
1. By high Reluctance at POLE TIPS:
At the time of construction we use chamfered poles. These
poles have larger air gap on the tips and smaller air gap at the
centre. These poles provide non-uniform air gap. The effect of
armature reaction is more near to edge of poles and
negligible near the centre of pole.
If air gap is kept non uniform i.e., larger air gap at the
edges(Pole Tip) and smaller near the centre of the pole and
then armature flux near the pole tip decreases and armature
reaction decreases.

9. Fig. High reluctance at pole tips

10. 2. By Laminated Pole Shoe:
We insert Laminated objects in the pole. By having Laminated
pole shoe the reluctance in the armature flux path
increases. Hence the armature flux gap gets reduced.

11. 3. By Reduction in Armature flux:
The effect of Armature Reaction is reduced by creating
more reluctance in the path of Armature flux. This is
achieved by using field Pole Laminations having several
Rectangular holes punched in them. It gives high
Reluctance in the path of armature flux. Due to this
armature cross flux reduces whereas main field remains
almost unaffected.

12. 4. By having Strong main magnetic field:
During the design of DC machine it should be ensured that the
main field m.m.f. is sufficiently strong in comparison with full
load armature flux.
Greater the main field, lesser will be the distortion.

13. 5) By using Inter Poles:
The effect of Armature reaction is reduced by interpoles
placed in between the main poles. The magnetic axis of
interpoles is in the Direction of q-axis. Interpoles
windings are connected in series with the armature
winding. So that, interpoles flux is able to neutralize the
effect of armature flux. The interpoles are narrow and
tapered with large air gap.

14. Fig. Interpoles are added [NN & SS]

15. 6. By Using Compensating Windings:
The Armature Reaction can also be limited by
compensating windings. It is the best and most
expensive methods. The compensating windings are
connected in series with armature winding.

16. That’s it
THANK YOU