LP11 5 FORE FINGER = MAGNETIC FIELD MIDDLE FINGER= CURRENT THUMB = MOTION FORCE = B IAl Fleming’s Left Hand Rule Or
Motor Rule

Slide 6:

LP11 6 FORE FINGER = MAGNETIC FIELD 900 900 900 MIDDLE FINGER = INDUCED
VOLTAGE THUMB = MOTION VOLTAGE = B l u Fleming’s Right Hand Rule Or
Generator Rule

Slide 7:

LP11 7 Action of a Commutator

Slide 8:

LP11 8 Armature of a DC Motor

Slide 9:

LP11 9 Generated Voltage in a DC Machine

Slide 10:

LP11 10 Summary of a DC Machine Basically consists of
An electromagnetic or permanent magnetic structure called
field which is static
An Armature which rotates
The Field produces a magnetic medium
The Armature produces voltage and torque under the action
of the magnetic field

Slide 11:

LP11 11 Voltage and Torque developed in a
DC Machine Induced EMF, EA = Km (volts)
Developed Torque, Tdev = KIA (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

Slide 12:

LP11 12 Interaction of Prime-mover DC Generator
and Load Prime-mover
(Turbine) DC Generator Load IA Tdev m EA + - VL + - Tpm EA is Generated voltage
VL is Load voltage
Tpm is the Torque generated by Prime Mover
Tdev is the opposing generator torque

Slide 13:

LP11 13 Interaction of the DC Motor
and Mechanical Load DC Motor Mechanical
Load
(Pump,
Compressor) Tload m EA + - 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 + - -

Slide 14:

LP11 14 Power Developed in a DC Machine Input mechanical power to dc generator
= Tdev m= KIAm =EA IA
= Output electric power to load Input electrical power to dc motor
= EA IA= K m IA = Tdev m
= Output mechanical power to load Neglecting Losses,

Slide 15:

LP11 15 Equivalence of motor and generator In every generator there is a motor (Tdev opposes Tpm)
In every motor there is a generator (EA opposes VT)

Slide 16:

LP11 16 Field Coil Armature RA Vf Separately Excited DC Machine + -

Slide 17:

LP11 17 Shunt Field Coil Armature RA Shunt Excited DC Machine

Slide 18:

LP11 18 Series Field Coil Armature RA Series Excited DC Machine

Slide 19:

LP11 19 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

Slide 20:

LP11 20 DC Machine-Example I A dc motor has Ra =2 , IA=5 A, EA = 220V, m = 1200 rpm.
Determine i) voltage applied to the armature, developed torque,
developed power . ii) Repeat with m = 1500 rpm. Assume same
IA. Solution on Greenboard

Slide 21:

LP11 21 Field Coil Armature RA Vf Separately Excited DC Motor
Torque-speed Characteristics + - m Tdev

Slide 22:

LP11 22 Series Field Coil Armature RA Series Excited DC Motor
Torque-Speed Characteristics m Tdev

Slide 23:

LP11 23 Speed Control of Separately Excited
DC Motor(2) 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 Tdev1 Tdev2 Tdev3 Tdev1<Tdev2< Tdev3

Slide 24:

LP11 24 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 below rated speed. m Tdev1 Tdev2 Tdev3 Tdev1<Tdev2< Tdev3

Slide 25:

LP11 25 A separately excited dc motor with negligible armature resistance
operates at 1800 rpm under no-load with VT =240V(rated voltage).
The rated speed of the motor is 1750 rpm.
i) Determine VT if the motor has to operate at 1200 rpm under no-load.
ii) Determine (flux/pole) if the motor has to operate at 2400 rpm
under no-load; given that K = 400/.
iii) Determine the rated flux per pole of the machine. DC Machine-Example II Solution on Greenboard

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