QUESTIONS ON DC MACHINE CONSTRUCTION

QUESTIONS ON DC MACHINE CONSTRUCTION

Q.1.
Why is armature core of a dc machine laminated  ?

Ans.
To reduce Eddy current loss.

Q.2.
What is function of armature in a dc generator ?

Ans.
The function of armature is to rotate the conductors in a uniform magnetic field and provide a path of very low reluctance to the magnetic flux.

Q.3.
Why is the air gap between the pole -pieces and the armature kept very small ?

Ans.
To reduce reluctance of the magnetic path.

Q.4.
What is best suited material for Commutator segments?

Ans.
Sivered copper containing about  0.05% silver.

Q.5.
What for brushes are employed in dc machines ?

Ans.
The brushes are employed to collect current from Commutator and supply it to the external load circuit.

Q.6.
Why are the graphite or carbon brushes preferred over copper brushes for use in dc machines?

Ans.
Due to self lubricating property.

Q.7.
Why are brushes staggered ?

Ans.
The brushes are staggered in order to prevent ridge formation on the surface of the Commutator.

Q.8.
Why fractional pitch winding is preferred over full pitch winding ?

Ans.
To affect saving in the copper of end connections and to have improved commutation.

Q.9.
What are the different types of armature windings used in dc machines ??

Ans.
Lap winding and wave windings.

Q.10.
For what type of dc machine ,wave winding is employed ?

Ans.
For low current and high voltage rating machines .

Q.11.
For what type of dc machine ,lap winding is employed ?

Ans.
For high current and low voltage rating machines .