This ppt contain presents construction and working of DC motor.

1. DC Motor Construction and Working

2. • Electric motors are the most important element of today's
industrial world.
• From a simple drill machine to a sophisticated robotic arm
electric motors are used everywhere .

3. Types
There are two types of electric motors-
1.AC Motors
2.DC Motors
•In these, because of some important characteristics like fast reaction, better speed
control, simple construction, DC motors are very popular in automatic machines.
AC motor
DC motor

4. After this slide you can watch a video
based on this PPT or you can skip it

5. Construction
•The outer part of the motor is
generally static, which is known
as stator.
•Stator consist of a frame, and it
contains “Pole Shoes” which
are projected inward.

6. Construction
•Core of these poles are made from silicon
steel on which insulated copper wire is wound
to make windings.
•These poles are bolted and fixed inside the
frame.
Core

7. Construction
• When DC current is pass through the windings it creates a static magnetic field.
• There are two types of pole in a DC machine.
1. Main/ Field Pole
2. Inter Poles

8. Construction
• The connections of these poles are brought out through connectors in
the terminal box, so that we can give electric supply to them and even
do the check for the fault.
• Main poles create static magnetic field, when current is pass to its
winding.

9. Construction
• In this magnetic field rotating part of motor lies, known as Rotor or Armature which
is made by number of stampings of highly permeable material i.e. silicon steel,
which allows magnetic field to pass through it easily.

10. Construction
• Slots are cut on the outer periphery of rotor or we can say “armature”, which
receive coils/windings made up of copper conductor.
• Each coil gets connected to an external DC source by a pair of commutator
segments arranged in the form of a Ring.

11. Construction
•This complete assembly is housed over a cylindrical shaft made up of high quality
steel.

12. Construction
• Because of the bearings at both side of the shaft the rotor is capable of rotate
between the field poles.

13. Working
• When electric current is
forced to pass through the
rotor conductors by a set of
carbon brushes through
commutator segments, it
creates their own magnetic
field which tries to distorts
the magnetic field, created
by the field pole.

14. • Due to interaction between two magnetic fields i.e magagntic field of main
poles and the rotor conductors. Electromagnetic Forces act on the rotor
conductors and these forces act tangentially on the rotor surface.
• Therefore a torque is produced at the rotor shaft and the rotor rotates.
.

15. • To understand the process more easily lets take a example of single loop having a
set of its own commutator segment.
Commutator
segments

16. • Due to the DC voltage applied by an external DC source current will flow in the
coil in given direction from positive to negative potential and by Fleming's left
hand rule , we can find that this side of coil receive force in upward direction
and this side will receive a downward force and hence the loop rotates.
Current

17. • During the rotation of loop you can find that commutator segments comes in
contact with brushes of opposite polarity one by one.
• This way the conductor of left side always carry current in given direction, and
of right side in opposite direction.

18. • This helps to maintain the continuous rotation of coil.
• We can also find that magnitude of force on the coil is maximum in this region
after that, magnitude reduce reduces considerably.
• This cause uneven torque and moment of rotor.
• To make “maximum torque” always available at the shaft of rotor multiple
number of coils with a pair of commutator segments are placed in the rotor.

19. •When one coil passes through the region of maximum torque next coil will take its place.
•This way shaft of rotor always provide higher and smooth torque.
•Coils are connected to commutator segment in such a way that every instant of time each and every
coil carries current, but the sides of coil to comes at the left hand side carries current in one direction
and the side at right hand carries current in opposite direction respective of the rotor position.
•This can be achieved by the lap or wave connection windings.
• To ensure that the current given to the commutator segments will not reach to the shaft Mica Insulation
is placed between them.

20. • In small DC motor permanent magnet can be use to create static magnetic field,
but they can loose their magnetism due to heating, vibration, or aging, that’s why
in higher rating motor electromagnets are used and their magnetic
field density can be controlled to control output torque.

21. Lets have a look at the coil design, if a single turn coil of thick wire is used here
then it allow higher current and give higher torque. Whereas, if multi-turn coil of
thin wire is used then current and torque is also reduced but we get higher speed
Single turn coil Multi- turn coil

22. • That means at the time of manufacturing we can decide whether we want high
torque low speed machine or low toque high speed machine.
• Here the work of interpole is to reduce sparking at the brushes over commutator
ring due to the effect of armature reaction.
• To energized the field poles we can use same DC source which runs our DC
motor or we can use a separated source , the method which is used will decide
the type of DC motor.
High torque low speed machine Low toque high speed machine

23. • At last all terminals are brought out through terminal box.

24. • And, “end covers” are fixed form both side, which holds bearings at both ends of
shaft.

25. •So this is about the Construction and Working of DC motor
• You can watch video of this Presentation at https://youtu.be/E9X_ZQDt670
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