DC and AC Motor Construction and Working Principle

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DC and AC motor almost operate in the same way and their construction is almost the same to
each other. But being that the AC motor is fed with the AC voltage and the DC motor is fed by
the DC current the two cannot be operated exactly the same and their construction cannot as well
be exactly the same. But for the two the principle of operation is the same which is based on
Faraday ́s law.
DC MOTOR
Contraction of DC motor
Here we will take consideration to a DC Shunt motor as an example of DC motor. This type of
a DC motor has all the basic parts which are field windings, armature and the commutator
(liang, 2013). The prototype of this type can be illustrated using the following diagram;

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Figure 1: Showing parts of the DC motor
(liang, 2013).
Yoke: This is the outer part of the motor and it is made up of cast iron or steel in some cases.
The importance of this part is only to provide the mechanical strength to the motor ́s whole
assembly and it also carries magnetic flux which is generated by the field winding.
Pole and Pole Shoes: The poles of the motor are joined to the yoke by the help of some bolts.
This pole carries field windings and pole shoes are fastened to the poles. Pole shoes help in
supporting the field coils and also spreading out the flux in the air gap evenly.
Field windings: These are made of copper, field coils are first wound and then put on each pole
and the connection is done in series. When these windings are energized they make North and
South Pole alternate. This is illustrated using the following diagram;
Figure 2: Showing field windings
(liang, 2013).
Armature core: This core is the rotor of the DC motor and it is cylindrical in shape having
several slots which always carry the armature windings. In most cases, it is built using laminated
circular steel to help reduce the eddy current losses.

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Commutator and brushes: The commutator is very basic in the DC motor construction, it
helps in collecting the current produced in the armature conductors. Brushes are made of
graphite or carbon, they always rest on commutator segments and slide on the segment as the
commutator rotates making the physical contact to supply or collect the current (Studer, 2011).
The commutator can be illustrated using the following diagram;
Figure 3: Showing commutators
(Studer, 2011).
Working principle of DC Shunt motor.
When the Shunt motor is supplied with the DC voltage it will draw very low current because of
high resistance. The more the number of turns in shunt the higher the strength of the magnetic
field. The motor will start moving when the field of the armature and the windings of the shunt
starts to interact. When the magnetic becomes stronger, the rotational torque increase hence
resulting in an increase in the speed of rotation of the motor.