3. HISTORY OF DC MOTOR:
In 1834, Russian engineer Moritz
von Jacobi went on to invent the very
first rotating DC motor. His invention
became famous for being incredibly
powerful, which later set a world
record. Incredibly, he broke his own
world record in 1838 with a new and
improved version of his DC motor
invention. This motor motivated others
to produce DC motors of the same
powerful standard, with the ability to
drive a boat with a capacity of 14
people across a river.
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4. WHAT IS AN ELECTRIC MOTOR?
An electric motor is an electromechanical device which
converts electrical energy into mechanical energy.
WHAT IS A DC MOTOR?
A direct current (dc) motor is a type of electric machine
that converts electrical energy into mechanical energy. DC
motors take electrical power through direct current, and
convert this energy into mechanical rotation.
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6. CONSTRUCTION:
A DC motor or machine consists of two windings namely field
winding and armature winding. The field winding is stationary and
the armature winding can rotate.
The field winding produces a magnetic flux in the air gap between
the armature and field windings and the armature is placed in this
magnetic field. The construction of DC motor or machine is shown
in the previous slide.
Parts used in construction of dc motor:
Yoke, Poles, Field winding, Commutator, Carbon brushes
Bearings, etc…
A brief description of the various parts is given in the next slide:
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7. YOKE:
The yoke acts as the outer cover of a DC motor and it is also known as the frame. The yoke is
an iron body, made up of low reluctance magnetic material such as cast iron, silicon steel,
rolled steel, etc.
Yoke serves two purposes, firstly it provides mechanical protection to the outer parts of the
machine secondly it provides a low reluctance path for the magnetic flux.
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8. 2. POLES AND POLE SHOE:
• The pole and pole shoe are fixed on the yoke by bolts. These are made
of thin cast steel or wrought iron laminations that are riveted together.
Poles produce the magnetic flux when the field winding is excited.
A Pole shoe is an extended part of a pole. Due to its shape, the pole
area is enlarged and more flux can pass through the air gap to the
armature.
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9. 3.FIELD WINDING
The coils around the poles are known as field (or exciting) coils and are
connected in series to form the field winding. Copper wire is used for the
construction of field coils. When the DC is passed through the field
windings, it magnetizes poles that produce magnetic flux.
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10. ARMATURE WINDING
The armature winding plays a very important role in the construction of a
DC motor because the conversion of power takes place in the armature
winding. Based on connections, there are two types of armature windings
named:
1. Wave Winding
2. Lap Winding 10
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11. COMMUTATOR
It is mounted on the shaft. It is made up of a large number of wedge-shaped
segments of hard drawn copper, insulated from each other by a thin layer of
mica.
The commutator connects the rotating armature conductor to the stationary
external circuit through carbon brushes. It converts alternating torque into
unidirectional torque produced in the armature. 11
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12. CARBON BRUSHES
The current is conducted from the voltage source to the armature by the
carbon brushes which are held against the surface of the commutator by
springs. They are made of high-grade carbon steel and are rectangular.
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13. BEARINGS
The ball or roller bearings are fitted in the end housings. The friction
between stationary and rotating parts of the motor is reduced by bearing.
Mostly high carbon steel is used for making the bearings as it is a very hard
material. 13
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14. WORKING PRINCIPLE OF DC MOTOR:
PRINCIPLE:
A current-carrying conductor, when kept
in a magnetic field, gains torque and
develops a tendency to move. In short,
when electric fields and magnetic fields
interact a mechanical force arises. This
is the principle on which the DC motors
work.
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16. WORKING:
A magnetic field arises in the air gap when the field coil of the DC motor
is energised. The created magnetic field is in the direction of the radii of
the armature. The magnetic field enters the armature from the North pole
side of the field coil and “exits” the armature from the South pole side of
the field coil.
The conductors located on the other pole are subjected to a force of the
same intensity but in the opposite direction. These two opposing forces
create a torque that causes the motor armature to rotate.
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17. TYPES OF DC MOTORS:
DC motors have a wide range of applications ranging from electric shavers to automobiles.
To cater to this wide range of applications, they are classified into different types based on
the field winding connections to the armature as:
Self Excited DC Motor:
1. Shunt wound DC motor
2. Series wound DC motor
3. Compound wound DC motor
Separately Excited DC Motor:
1. Brushed DC Motor
2. Brushless DC Motor
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18. Self Excited DC Motors:
1. Shunt wound DC Motor
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21. Separately excited DC Motor:
1. Brushed DC Motor 2. Brushless DC Motor
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22. APPLICATIONS:
1. Shunt DC Motor
Characteristics:
Speed is fairly constant and medium starting torque.
Applications:
1. Blowers and fans
2. Centrifugal and reciprocating pumps
3. Lathe machines
4. Machine tools
5. Milling machines
6. Drilling machines
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23. 2. Series DC Motor
Characteristics:
Series High starting torque.
No load condition is dangerous.
Variable speed.
Applications:
1. Cranes
2. Hoists, Elevators
3. Trolleys
4. Conveyors
5. Electric locomotives
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24. 3. Cumulative compound DC Motor
Characteristics:
High starting torque.
No load condition is allowed.
Applications:
1. Rolling mills
2. Punches
3. Shears
4. Heavy planers
5. Elevators
Differential compound DC Motor
Characteristics:
Speed increases as load increases.
Applications:
Not suitable for any practical applications
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25. CONCLUSION :
Machines play a vital role in the improvisation of our day to day lifestyle and
DC Motor is one of them.
Can you imagine climbing a 30 storeyed building all by yourself without
making use of elevator or peddling a boat for 24 hours just to reach your
destination? Believe it or not, DC Motors have actually made our life much
easier with its widespread applicattions in our day to day life. Hence I’d like
to conclude by quoting that-
“MACHINERY IS THE SUBCONSIOUS MIND OF THE WORLD”
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26. REFERENCE:
“A TEXTBOOK OF ELECTRICAL TECHNOLOGY”
- B. L. Theraja , A. K. Theraja.
“ELECTRIC MOTOR DRIVES”
-Krishnan.
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