DC Machines

124 Pages·2012·11.85 MB·English

by  Mohamed Magdy Ahmed

DC Machines
Chapter 1: Theory Of Operation & Construction

Chapter 2: DC Machines On Load

Chapter 3: DC Generators

Chapter 4: DC Motors

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References
S.J. Chapman, "Electric Machinery Fundamentals",
McGraw Hill, 4th edition, 2005.
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Chapter 1
Theory Of Operation & Construction
1. Introduction
2. Electromechanical Energy Conversion
3. DC Machines Theory of Operation
4. Construction
5. Classification of DC Machines
6. Armature Voltage and Developed Torque
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Electric Machine
Mechanical Electrical Electrical Mechanical
Motor
Generator
Input Output Input Output
Electromechanical Energy Conversion
i
+ w T Mechanical system
v
Electrical system
Ideal Electric Machine
_
Motor
Energy Flow v i=T w
Generator
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Principle of Operation
If a conductor of length l moves at a linear speed v in a
magnetic field the induced voltage in the conductor is
Faraday’s law or
e=Blv
e
e
flux cutting rule N
v
v
B
S
B
Right hand rule
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Principle of Operation
For the current carrying conductor of length l the
force known as Lorentz force produced is
i
i
N
F
F
F=Bli
B
S
B
Left hand rule
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Induced e.m.f e
e
 N
v
v
B
e = B l v
S
B
Right hand rule
Electromagnetic Force

i
i
N
F
F
B
F = B l i
S
B
Lift hand rule 7
DC Machines theory of operation
N N e N
e
e
w
w
w
S
S S
and for multiturn machine
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Generated Voltage (EMF)
For counter-clockwise motion the rotor terminal under

the N pole is always positive with respect to that
under the S pole.
The brush terminal B1 is always positive and B2 is

negative so e12 is unidirectional
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DC Machines
DC currents are required for both its field winding
( stator ) and armature winding (Rotor)
DC machine mainly used as DC motors
DC motors is characterized by superior torque
and a wide range of speed
DC machine is more costly than comparable AC
machine and their maintenance cost is higher.
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