1 dc machine
TRANSCRIPT
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 1/23
LP11 1
Basics of a Electric Motor
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 3/23
LP11 3
A Four Pole DC Motor
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 4/23
LP11 4
Operating Principle of a DC Machine
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 5/23
LP11 5
FORE FINGER = MAGNETIC FIELD
900
900
900
MIDDLE FINGER= CURRENT
FORCE = B I Al
Fleming’s Left Hand Rule Or
Motor Rule
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 6/23
LP11 6
FORE FINGER = MAGNETIC FIELD
900 900
900
MIDDLE FINGER = INDUCED
VOLTAGE
VOLTAGE = B l u
Fleming’s Right Hand Rule Or
Generator Rule
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 7/23
LP11 7
Action of a Commutator
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 8/23
LP11 8
Armature of a DC Motor
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 9/23
LP11 9
Generated Voltage in a DC Machine
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 10/23
LP11 10
Summary of a DC Machine
• Basically consists of
1. An electromagnetic or permanent magnetic structure called
field which is static
2. An Armature which rotates
• The Field produces a magnetic medium
• The Armature produces voltage and torque under the action
of the magnetic field
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 11/23
LP11 11
Voltage and Torque developed in a
DC Machine
•Induced EMF, EA = K m (volts)
•Developed Torque, Tdev = K 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 the
Armature current
K is the machine constant
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 12/23
LP11 12
Interaction of Prime-mover DC Generator
and Load
Prime-mover (Turbine)
DC Generator L o a
d
IA Tdev
m EA
+
-
VL
+
-T pm
EA is Generated voltage
VL is Load voltage
T pm is the Torque generated by Prime Mover
Tdev is the opposing generator torque
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 13/23
LP11 13
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
+
--
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 14/23
LP11 14
Power Developed in a DC Machine
• Input mechanical power to dc generator
= Tdevm= K IAm =EA IA
= Output electric power to load
• Input electrical power to dc motor
= EA IA= K m IA = Tdevm
= Output mechanical power to load
Neglecting Losses,
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 15/23
LP11 15
Equivalence of motor and generator
•In every generator there is a motor (Tdev opposes T pm)
•In every motor there is a generator (EA opposes VT)
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 16/23
LP11 16
Field Coil
Armature
R A
Vf
Separately Excited DC Machine
+
-
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 17/23
LP11 17
Shunt Field Coil Armature
R A
Shunt Excited DC Machine
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 18/23
LP11 18
Series Field Coil
Armature
R A
Series Excited DC Machine
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 19/23
LP11 19
Shunt Field Coil Armature
R A
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
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 20/23
LP11 20
Field Coil
Armature
R A
Vf
Separately Excited DC Motor
Torque-speed Characteristics
+
-
m
Tdev
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 21/23
LP11 21
Series Field Coil
Armature
R A
Series Excited DC Motor
Torque-Speed Characteristics
m
Tdev
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 22/23
LP11 22
Speed Control of Separately Excited
DC Motor(2)
•By Controlling Terminal Voltage V T and keeping If or constant at rated value .This method of speed control is applicable
for speeds below rated or base speed.
m
VT
Tdev1 Tdev2 Tdev3
Tdev1
<Tdev2
< Tdev3
7/28/2019 1 Dc Machine
http://slidepdf.com/reader/full/1-dc-machine 23/23
LP11 23
Speed Control of Separately Excited
DC Motor
•By Controlling (reducing) Field Current I f or and keepingVT at rated value. This method of speed control is applicable
for speeds below rated speed.
m
Tdev1
Tdev2 Tdev3
Tdev1<Tdev2< Tdev3