(a) have maximum emf at the output terminals.
(b) have maximum emf generated in the armature.
(c) have minimum heat dissipation from the armature.
(d) make the armature dynamically balanced.
Answer: (d) make the armature dynamically balanced.
Explanation:
CONCEPT: Distributed Armature Winding
- In
DC machines, armature windings are placed on the rotor.
- These
windings are not concentrated in only two slots but are distributed
over many slots around the armature periphery.
- Such
a winding is called a distributed armature winding.
EXPLANATION
- When
armature coils are distributed into many slots:
- The mass
of copper is uniformly spread around the rotor.
- This
uniform distribution:
- Prevents
uneven mass concentration
- Avoids
vibration during rotation
- Hence,
the armature becomes dynamically balanced, allowing:
- Smooth
rotation
- Reduced
mechanical stress on bearings
- Longer
machine life
Additional Benefits (Secondary)
- Distributed
windings also:
- Improve
the voltage waveform
- Reduce
harmonic content
- Improve
commutation
- However,
these are electrical advantages, while the primary
reason is mechanical balancing.
Why Other Options Are Incorrect
(a) Have maximum EMF ❌
- Maximum
EMF depends on:
- Flux
- Speed
- Number
of conductors
- Distributed
winding mainly improves EMF quality, not maximum EMF value.
(b) Have maximum current ❌
- Current
capacity depends on:
- Conductor
size
- Cooling
- Parallel
paths
- Distribution
of coils does not directly increase current capacity.
(c) Have minimum heat dissipation ❌
- Heat
dissipation depends on:
- Losses
- Cooling
arrangement
- Coil
distribution may help indirectly, but it is not the main reason.
Construction Reminder (Important Note)
- DC
Machine:
- Armature
winding → Rotor
- Field
winding → Stator
- AC
Machine:
- Armature
winding → Stator
- Field
winding → Rotor
FINAL CONCLUSION
- Distributing
armature coils into many slots mainly helps to:
- Therefore,
the correct answer is:
Correct Answer
✅ Option (d): Make the
armature dynamically balanced
✔️ Key One-Line Exam Statement
Armature coils in a DC machine are distributed in many
slots primarily to achieve dynamic balancing of the rotor.