Construction of DC Motor
A DC Motor like we all know is a device
that deals in the conversion of Electrical energy to mechanical energy and this
is essentially brought about by two major parts required for the construction
of dc motor, namely.
1)
Stator – The static part that houses the field
windings and receives the supply and
2)
Rotor
– The rotating part that brings about the mechanical rotations.
Other than
that there are several subsidiary parts namely the
3)
Yoke
or casting of dc motor.
4)
Magnetic
poles of dc motor.
5)
Field
winding of dc motor.
6)
Armature
winding of dc motor.
7)
Commutator
of dc motor.
8)
Brushes
of dc motor.
All these parts put together configures
the total construction of a dc motor\, that has
been pictorially represented in the diagram below.
Now let’s
do a detailed discussion about all the essencial parts of dc motor.
Construction of yoke of dc motor
The
magnetic frame or the yoke of dc machine made up of cast iron or steel and
forms an integral part of the stator or the static part of the motor. Its main function
is to form a protective covering over the inner sophisticated parts of the
motor and provide support to the armature. It also supports the field system by
housing the magnetic poles and field windings of the dc motor.
Construction of Magnetic poles of dc motor
The
magnetic poles are structures fitted onto the inner wall of the yoke with
screws. The construction of magnetic poles basically comprises of two parts namely,
the pole core and the pole shoe stacked together under hydraulic pressure and
then attached to the yoke. These two structures are assigned for different
purposes, the pole core is of small
cross sectional area and its function is to just hold the pole shoe over the
yoke, whereas the pole shoe having a relatively larger cross-sectional area spreads
the flux produced over the air gap between the stator and rotor to reduce the loss
due to reluctance. The pole shoe also carries slots for the field windings that
produce the field flux.
Construction of field winding of dc motor
The field
windings of the dc motor are made with field coils (copper wire) wound over the
slots of the pole shoes in such a manner that when field current flows through
it, then adjacent poles have opposite polarity are produced.
The field
windings basically form an electromagnet, that produces field flux within which
the rotor armature of the dc motor rotates, and results in the effective flux
cutting.
Construction of Armature winding of dc motor
The armature
of the dc motor is attached to the rotor, or the rotating part of the machine,
and as a result is subjected to altering magnetic field in the path of its
rotation which directly results in magnetic losses. For this reason the rotor is made of armature
core, that’s made with several low-hysteresis silicon steel laminations, to
reduce the magnetic losses like hysteresis and eddy current loss respectively. These
laminated steel sheets are stacked together to form the cylindrical structure
of the armature core.
The
armature core are provided with slots made of the same material as the core to
which the armature windings made with several turns of copper wire distributed
uniformly over the entire periphery of the core. The slot openings a shut with
fibrous wedges to prevent the conductor from plying out due to the high
centrifugal force produced during the rotation of the armature, in presence of
supply current and field.
The
construction of armature winding of dc motor can be of two types:-
i) Lap Wnding-
In this case the number of parallel paths between conductors
A is equal to the number of poles P.
i.e A = P
***An easy way of
remembering it is by remembering the word LAP-----à L A=P
ii) Wave Winding–
Here in this case, the number of parallel paths between
conductors A is always equal to 2 irrespective of the number of poles. <br/>Hence
the machine designs are made accordingly.
Construction of commutator of dc motor
The commutator
of a dc motor is a cylindrical structure made up of copper segments stacked
together, but insulated from each other by mica. Its main function as far as
the dc motor is concerned is to commute or relay the supply current from the
mains to the armature windings housed over a rotating structure through the
brushes of dc motor.
Construction of Brushes of DC Motor
The brushes
of dc motor are made with carbon or graphite structures, making sliding contact
over the rotating commutator. The brushes are used to relay the current from
external circuit to the rotating commutator form where it flows into the
armature windings. ∴ the commutator and brush unit of the dc motor
is concernied with transmitting the power from the static electrical circult to
the mechanically rotating region or the rotor.
