PPT ON ARMATURE REACTION IN DC MACHINE AND ITS EFFECTS

1. Armature ReactionArmature Reaction
Contents
• Armature Reaction
• Compensating Winding
• Interpoles
Ashish Bohra

2. POLE
FACE
ARMATURE
YOKE
N
S
BRUSH
Armature Reaction is the
effect of “Armature Field”
on the “ main Field “.
Armature field is the field
which is produced by the
armature conductors due to
current flowing through
them.
Main field is the field
which is produced by the
poles which is necessary
for the operation.
Armature Reaction In DC Machine
DC Generator
Gen. Rotation

3. Motion
Magnetic
Field
Current
Direction of current running through conductor
Fleming’s Right Hand Rule

4. N
S
q - axis
GNA
d- axis
Current
Magnetic
Field
Magnetic
Field
Direction of Magnetic Field due to Armature
Conductor Current
Right Hand Thumb Rule

5. d- axis
Field MMF (Fm)
GNA
MNA (At no load )
AO
Flux due to field
current alone
d- axis
Main Field Flux produced by field m.m.f at no load

6. N
S
d- axis
Armature MMF (Fa)
GNA
q - axis
O
B
q - axis
Flux due to
Armature
current alone
d- axis
GNA
Armature Field Flux produced by Armature m.m.f with
field unexcited
Gen. Rotation

7. d - axis
Fa
d- axis
Fm
GNA
MNA (At on load )
AO
FR
θ
Resultant of Main Field Flux and Armature Field Flux

8. N
SPolar Axis
d- Axis
Geometric Neutral Axis
Interpolar Axis
q - Axis
GNA and MNA Axis

9. S
N
Polar Axis
d- Axis
Geometric Neutral Axis
Interpolar Axis
q - Axis

10. S
N
Polar Axis
d- Axis
Geometric Neutral Axis
Interpolar Axis
q - Axis

11. S
N
Polar Axis
d- Axis
Geometric Neutral Axis
Interpolar Axis
q - Axis

12. S
N
Polar Axis
d- Axis
Geometric Neutral Axis
Interpolar Axis
q - Axis

13. S
N
Polar Axis Interpolar Axis Polar Axis

14. Generator
Direction
N
N
x x x x x x
N S
Polar Axis Interpolar Axis Polar AxisMotor
Direction GNA
MNA
Bm Fa
Ba
ϕ
Flux distribution and Flux waveforms due to Field and
Armature currents
ϕm
ϕa

15. Peaky wave
Mmf
& B
Resultant Flux waveform
ϕ

16. Resultant Flux waveform and MNA shift
MNA
ϕ

17. ϕR
x
Mmf
& B
Shift
of
MNA
Resultant Flux waveform and Brush Shift
ϕ

18. Demagnetizing Effect due to Brush Shift in DC Machine
DemagnetizationGNA
MNA (At no load )

19. Effects of armature Reaction
1) Distortion of the main field flux wave along the air gap periphery.
2) Net reduction in the main field flux per pole.
N
SP Axis
d- Axis
GNA I.P.A
q - Axis
Cross
Magnetization Demagnetization

20. Compensating
Winding
Polar Axis
d- Axis
GNA
Interpolar Axis
q - Axis
Compensating Winding at slot in pole faces

21. Resultant Flux waveform with compensating winding
(practically not possible)
ϕm
ϕa
ϕc= - ϕa
ϕ

22. Resultant Flux waveform with Practical compensating winding
ϕm
ϕa ϕc
ϕ

23. POLE
FACE
ARMATUR
E
YOKE
N
S
BRUSH
Interpoles for DC Generator
Gen. Rotation
S
N
INTERPOLES

24. Resultant Flux waveform without Interpoles
ϕR
ϕ

25. Resultant Flux waveform with Interpoles
Interpoles
ϕm
ϕm
ϕ

26. Thank you