Study of constructional feature of D.C
machine
machine
Theory:
DC machine can be run as a generator as well as a motor. There is no
difference according to construction.
difference according to construction.
The main part of the DC machine:
1. yock/frame 2. Pole core
3. Field winding 4. Armature core
5. Interpol 6. Carbon Brush with brush holder
7. commutator 8. Rocker9Side covers
9. Side covers 10. Shaft
1.Body:
In this outer frame of the machine made of cast iron. It serves a double purpose.
(a) it provides mechanical support for poles as well as mechanical protection.
(b) it carries the magnetic flux path produced by the pole.
2. Pole core & pole shoes:
Pole core are inserted inside the yoke. Pole shoes are also attached with pole
core. The pole shoes spread out the flux in the air gap as well as support the
field coils. Pole core & pole shoes and laminated to avoid eddy current losses.
core. The pole shoes spread out the flux in the air gap as well as support the
field coils. Pole core & pole shoes and laminated to avoid eddy current losses.
3. Field Winding / field coils:
The coils, which consist of copper wire or strip wound on pole core are called
field coils or field winding. When current is passed through these cils, the pole
energises & produces the exciting flux. This flux is cut by an armature conductor.
field coils or field winding. When current is passed through these cils, the pole
energises & produces the exciting flux. This flux is cut by an armature conductor.
4. Armature & Armature Windings:
The cylindrical-shaped moving part between field poles inside the dc machine
is called the armature. It builts of circular shaped iron on steek thin discs to avoid
eddy current losses. These discs insulated with each other. There are slots
insides the discs. When the discs / strips are joined together, then appears
slots parallel to the shaft. Insulated coils are inserted in these slots, collectively all these coils are called armature winding.
is called the armature. It builts of circular shaped iron on steek thin discs to avoid
eddy current losses. These discs insulated with each other. There are slots
insides the discs. When the discs / strips are joined together, then appears
slots parallel to the shaft. Insulated coils are inserted in these slots, collectively all these coils are called armature winding.
5. Interpol's or Commutating Poles:
Extra small poles are instead in the internal surfaces of the yock / frame
between main poles. These poles are called interpoles or commutating poles.
Their purpose is to stop sparking on commutator amand minimized the effect
of armature reaction. These are made of laminated or solid wrought iron or mild
steel material.
between main poles. These poles are called interpoles or commutating poles.
Their purpose is to stop sparking on commutator amand minimized the effect
of armature reaction. These are made of laminated or solid wrought iron or mild
steel material.
6. Commulator:
It is of cylindrical structure which is fitted on an armature shaft at a distance
of armature. It is made of small rectangular copper segments which are
of armature. It is made of small rectangular copper segments which are
insulated from each other by layers of mica. The function of the commutator is
to facilitate collection of current from the commutator and convert AC to DC
(pulsating) in the external load circuit.
7. Carbon brush with brush holder.
Carbon branches are used to collect frome commutator. These are usually
made of carbon or graphite and are in the shape of a rectangular block.
These are housed in brush holders. The brushes can slide on the commulator
by a spring. The spring tension can be adjusted by changing the position of the
layer in the notches. A flexible copper pigtail mounted at the top of the brush.
Current from the brushes to the terminals.
made of carbon or graphite and are in the shape of a rectangular block.
These are housed in brush holders. The brushes can slide on the commulator
by a spring. The spring tension can be adjusted by changing the position of the
layer in the notches. A flexible copper pigtail mounted at the top of the brush.
Current from the brushes to the terminals.
8. Rocker:
The carbon brushes should be in an accurate position and commutator. For this
purpose, a rocker is used. Brush assembly (brush hold & spring ect) is mounted
on a non-metallic circular shape, which can be adjusted by hab]nd or handles,
this part is called Rocker.
purpose, a rocker is used. Brush assembly (brush hold & spring ect) is mounted
on a non-metallic circular shape, which can be adjusted by hab]nd or handles,
this part is called Rocker.
9. Slide covers:
On the both sides of DC machines side covers are fitted. There are holes in
these side covers for ventilation. Bearings are fitted in these side covers.
these side covers for ventilation. Bearings are fitted in these side covers.
10. Shaft:
It is a solid iron bar on which an armature assembly is fitted. Its both ends
are fitted in the bearing.
are fitted in the bearing.
11. Bearing:
To minimize friction losses of the machine, bearings are used. Armature can
move very easily with bearings . bearings are mounted on the both sides of
the armature shaft & these are supported with side covers.
move very easily with bearings . bearings are mounted on the both sides of
the armature shaft & these are supported with side covers.
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