The document discusses direct current (DC) machines, including their working principles, construction, and key components. It begins with an introduction and overview of Fleming's left-hand and right-hand rules for determining the direction of force on a current-carrying conductor in a magnetic field or induced electromotive force (emf) in a conductor. The working principle of a DC generator is then explained, where mechanical energy is converted to electrical energy using conductors and a magnetic field. Key parts of a DC machine like the field system, armature, commutator, and brushes are also described. Finally, the document concludes with references for further reading on electrical machines.

1. S.RAGUL,
ASSISTANT PROFESSOR, DEPARTMENT OF EEE,
KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY
DC MACHINES
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Content:
 Introduction to LAW and rules
 Working principle , construction and important parts.
 References

3. Fleming’s left hand rule
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4. Fleming’s left hand rule
Used to determine the direction of force acting
on a current carrying conductor placed in a
magnetic field .
The middle finger , the fore finger and thumb of
the left hand are kept at right angles to one
another .
The middle finger represent the direction
of current
The fore finger represent the direction of
magnetic field
The thumb will indicate the direction of
force acting on the conductor .
This rule is used in motors.4

5. Fleming’s Right hand rule
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6. Fleming’s Right hand rule
Used to determine the direction of emf induced
in a conductor
The middle finger , the fore finger and thumb of
the left hand are kept at right angles to one
another.
The fore finger represent the direction
of magnetic field
The thumb represent the direction of
motion of the conductor
The middle finger will indicate the
direction of the inducted emf .
This rule is used in DC Generators6

7. Len’s Law
The direction of induced emf is given by
Lenz’s law .
According to this law, the induced emf will
be acting in such a way so as to oppose the
very cause of production of it .
e = -N (dØ/dt) volts
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8. DC Generator
Mechanical energy is converted to electric
energy
Three requirements are essential
1. Conductors
2. Magnetic field
3. Mechanical energy
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9. Working principle
A generator works on the principles of
Faraday’s law of electromagnetic induction
Whenever a conductor is moved in the
magnetic field , an emf is induced and the
magnitude of the induced emf is directly
proportional to the rate of change of flux
linkage.
This emf causes a current flow if the
conductor circuit is closed .
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10. DC Machine
Commutator
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11. Sectional view of a DC machine
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12. Construction of DC Generator
Field system
Armature core
Armature
winding
Commutator
Brushes
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13. Field winding
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14. Rotor and rotor winding
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15. Working principle of DC motor
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16. Working principle of DC motor
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17. Force in DC motor
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18. Armature winding
There are 2 types of winding
Lap and Wave winding
Lap winding
A = P
The armature
windings are
divided into
no. of sections
equal to the no
of poles
Wave winding
A = 2
It is used in low
current output
and high voltage.
2 brushes
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19. Field system
It is for uniform magnetic field within
which the armature rotates.
Electromagnets are preferred in
comparison with permanent magnets
They are cheap , smaller in size ,
produce greater magnetic effect and
Field strength can be varied
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20. Field system consists of the
following parts
Yoke
Pole cores
Pole shoes
Field coils
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21. Armature core
The armature core is cylindrical
High permeability silicon steel
stampings
Impregnated
Lamination is to reduce the eddy
current loss
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22. Commutator
Connect with external circuit
Converts ac into unidirectional current
Cylindrical in shape
Made of wedge shaped copper segments
Segments are insulated from each other
Each commutator segment is connected to
armature conductors by means of a cu strip called
riser.
No of segments equal to no of coils
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23. Carbon brush
Carbon brushes are used in DC machines
because they are soft materials
It does not generate spikes when they contact
commutator
To deliver the current thro armature
Carbon is used for brushes because it has
negative temperature coefficient of resistance
Self lubricating , takes its shape , improving
area of contact
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24. Brush rock and holder
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25. Carbon brush
Brush leads (pig tails)
Brush rocker ( brush gear )
Front end cover
Rear end cover
Cooling fan
Bearing
Terminal box
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Conclusion:
The DC machines working principle, construction and different parts of
machine is explained in detail with suitable diagrams.
References:
• 1.P. C. Sen., ‘Principles of Electrical Machines and Power Electronics’, John
Wiley & Sons, 1997.
• 2.Deshpande M. V., “Electrical Machines” PHI Learning Pvt. Ltd., New
Delhi, 2011.
• 3.P.S. Bimbhra, ‘Electrical Machinery’, Khanna Publishers, 2003.
• 4.S.Sarma & K.Pathak “Electric Machines”, Cengage Learning India (P) Ltd.,
Delhi, 2011.
• 5.U.A.Bakshi&M.N.Bakshi “Electric Machines-I”,Technical publications,
2015.
• 6.Other Web Sources