contruction and working

1. DC MOTOR
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2. INTRODUCTION
A motor is a machine which converts
electrical energy into mechanical energy. A
DC motor finds application in rolling
mills, in traction system and overhead
cranes. The principle of operation of DC
motor is that when a current carrying
conductor is kept in a magnetic field, a
force is produced in that conductor.
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3. BACK EMF
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4. TORQUE EQUATION
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5. ARMATURE REACTION
If the magnetic field windings of a DC machine
are connected to the power source and the
rotor is turned by an external means, a voltage
will be induced in the conductors of the rotor.
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6. ARMATURE REACTION
This voltage is rectified and can be supplied to
external loads. However, if a load is connected, a
current will flow through the armature winding.
This current produces its own magnetic field
that distorts the original magnetic field from the
machine’s poles. This distortion of the machine’s
flux as the load increases is called armature
reaction.
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7. TYPES OF DC MOTOR
i) Permanent magnet DC motor
ii) Separately excited DC motor
iii) Series DC motor
iv) Shunt DC motor
v) Compound DC motor
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8. Permanent Magnet DC Motor
In this type of DC motor, the field is
made up of permanent magnet and
hence, it requires no field winding.
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9. Separately Excited DC Motor
Both the field
winding and the
armature
winding are fed
from two
different
sources,
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10. Series DC Motor
The field winding is
connected in series
with the armature
winding.
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11. Shunt DC Motor
The field
winding is
connected in
parallel with
the armature
winding.
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12. Compound DC Motor
A compound DC motor has both series
and shunt field winding. It can be a
short-shunt DC compound motor or a
long-shunt DC compound motor.
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13. Speed of DC Motor
Speed of a DC motor
depends on the
i) Supply voltage
ii) Armature current
iii) Armature
resistance
iv) Field flux.
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14. Characteristics of a DC Shunt
Motor
Speed versus armature current characteristics
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15. Characteristics of a DC Shunt
Motor
Torque versus armature current characteristics
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16. Characteristics of a DC Shunt
Motor
Speed–Torque characteristics
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17. Characteristics of a DC Series
Motor
Speed versus armature current characteristics
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18. Characteristics of a DC Series
Motor
Torque versus armature current characteristics
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19. Characteristics of a DC Series
Motor
Speed–Torque characteristics
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20. Characteristics of a DC Compound
Motor
Speed versus armature current characteristics
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21. Characteristics of a DC Compound
Motor
Torque versus armature current characteristics
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22. Characteristics of a DC compound
Motor
Speed Torque characteristics
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23. DC MOTOR STARTER
Since the armature resistance is small, generally
less than 1Ω, the current through the armature
at the time of starting will be very high. This
large current may damage the armature winding,
brushes and commutator segments
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24. DC MOTOR STARTER
Due to the high inrush of current at the time of
starting the motor, it becomes necessary to limit
this current to a safe value, which is generally
obtained by connecting an extra resistance in
series with the armature winding.
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25. Three-point Starter for DC Shunt
Motor
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26. Four-point Starter for DC Shunt
Motor
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27. SPEED CONTROL OF DC SHUNT
MOTOR
The different methods of speed control of DC shunt
motor are as follows:
i) Shunt field control or flux control method.
ii) Armature resistance control or armature control
method.
iii) Voltage control method.
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28. Field Control
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29. Armature Control OR
Armature Resistance Control
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30. SPEED CONTROL OF DC SERIES
MOTOR
There are three methods of speed control for DC series
motor, namely,
i) Flux control method
ii) Armature control method
iii) Series-parallel control.
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31. ELECTRIC BRAKING
 Braking is used to stop the motor quickly.
There are three types of electric braking.
i) Rheostatic or dynamic braking
ii) Braking by plugging
iii) Regenerative braking
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