This document provides information about different types of DC motors and their components and functioning. It discusses separately excited DC motors, shunt DC motors, series DC motors and compound DC motors. It describes the torque-speed characteristics and speed control methods for separately excited and shunt DC motors. The document also mentions induction motors, synchronous motors, single phase and three phase induction motors. It discusses concepts like magnetic field, current, Fleming's left hand rule and losses in AC machines.

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Today’s Topic

3. Name ID
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MD:Al-Amin Mallik 143-33-2100
Lipi Gosh 143-33-2099
Noyon 143-33-2231
MD:Mahbub Alam 143-33-2256

4. Defination:
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An electrical motor is a electrical
machine that converts electrical
energy into mechanical energy .

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Basics of a Electric Motor

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Field Coil
Armature
R
a
Vf
Separately Excited DC Motor
+
-
Rf
Vt
+
-
If
Ia
+
-
Ea
Armature equation: Ea=Vt-IaRa
Ea=Kam
Field equation: Vf=RfIf

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Field Coil
Armature
RA
Vf
Separately Excited DC Motor
Torque-speed Characteristics
+
-
m
T
T
K
R
K
V
a
a
a
t
m 2
)( 
 
Mechanical Load
+
-

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Speed Control of Separately Excited
DC Motor
•By Controlling(reducing) Field Current If or  and keeping
Vt at rated value. This method of speed control is applicable
for speeds above rated speed.
m
T1
T2
T3
T1<T2<
T3

T
K
R
K
V
a
a
a
t
m 2
)( 
 
1
1>  2>  3
2
3

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dc shunt motor
Field equation: Vt=Rf If
Rf=Rfw+Rfc
Armature equation: Vt=Ea+Ia Ra
Ea=Kam
Shunt Field Coil
Armature
R
a
If Ia
Ia – If
Vt
+
-
Rfc
Ea
+
-
Field coil has Rfw :
Implicit field resistance
Mechanical Load

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Field Coil
Armature
RA
Vf
Separately Excited DC Machine
+
-

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Shunt Field Coil Armature
RA
Shunt Excited DC Machine

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Shunt Field Coil Armature
RA
Compound Excited DC Machine
Series Field Coil
•If the shunt and series field aid each other it is called a cumulatively
excited machine
•If the shunt and series field oppose each other it is called a differentially
excited machine

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Series Field Coil
Armature
RA
Series Excited DC Machine

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Series Field Coil
Armature
Ra
Series Excited DC Motor
Torque-Speed Characteristics
m
T
sr
aesra
sr
t
m
K
RRR
TK
V 

Rsr Rae
-
+

18. Synchronous motor
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19. Induction motor
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20. Single phase induction motor
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21. Three phase induction motor

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FORE FINGER = MAGNETIC FIELD
900
900
900
MIDDLE FINGER= CURRENT
FORCE = B IAl
Fleming’s Left Hand Rule Or
Motor Rule

24. Electric motor rotor (left) and
stator (right)
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Lap Winding of a DC Machine
• Used in high current
low voltage circuits
•Number of parallel paths
equals number of brushes
or poles

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Wave Winding of a DC Machine
• Used in high voltage
low current circuits
•Number of parallel paths
always equals 2

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Voltage and Torque developed in a
DC Machine
•Induced EMF, Ea = Kam (volts)
•Developed Torque, Tdev = KaIa (Newton-meter
or Nm)
where m is the speed of the armature in rad/sec.,
 is the flux per pole in weber (Wb)
Ia is theArmature current
Ka is the machine constant

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Interaction of the DC Motor
and Mechanical Load
DC Motor
Mechanical
Load
(Pump,
Compressor)
Tload
mEa
+
- Tdev
Ea is Back EMF
VT is Applied voltage
Tdev is the Torque developed by DC Motor
Tload is the opposing load torque
Ia
VT
+
--

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Speed Control of Separately Excited
DC Motor
•By Controlling Terminal Voltage Vt and keeping If or 
constant at rated value .This method of speed control is applicable
for speeds below rated or base speed.
m
VT
T1 T2 T3
T1<T2< T3
T
K
R
K
V
a
a
a
t
m 2
)( 
 
V1<V2<V3
V1
V2 V3

30. Losses in AC machines
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Resistive losses (I2R) in the stator circuit
Resistive losses (I2R) in the rotor circuit
Iron losses due to fundamental frequency ac flux in the core. These are mostly in the
stator core.
Mechanical losses. These include friction in the bearings and a term called windage.
(wind (like the weather) -age) Windage is due to air turbulance and shear as the rotor
and stator move past each other
Stray losses. The other parts that aren't easily calculated. These include harmonic losses
in the core and current flow throuhg the core (rather than staying in the conductors
where you would like it to be)

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