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dcmotor 1
Suresh Chandra Kumawat
Batch-B2Roll No.-10MUBEEE120
PPt- Dc Motor
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Basics of a Electric Motor
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A Two Pole DC Motor
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dcmotor 4
A Four Pole DC Motor
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dcmotor 5
Operating Principle of a DC Machine
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FOREFINGER = MAGNETIC FIELD
900
900
900
MIDDLE FINGER= CURRENT
FORCE = BIAl
Flemings Left Hand Rule Or
Motor Rule
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Armature of a DC Motor
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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
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Voltage and Torque developed in a
DC Machine
Induced EMF, Ea= Kam (volts)
Developed Torque, Tdev= KaIa(Newton-meter
or Nm)
where mis the speed of the armature in rad/sec.,
is the flux per pole in weber (Wb)
Ia
is the
Armature current
Kais the machine constant
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Field Coil
Armature
RA
Vf
Separately Excited DC Motor
Torque-speed Characteristics
+
-
m
T
TK
R
K
V
a
a
a
t
m 2
)(
Mechanical Load
+
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dcmotor 11
Separately excited DC Motor-Example I
A dc motor has Ra=2 , Ia=5 A, Ea= 220V, Nm= 1200 rpm.Determine
i) voltage applied to the armature, developed torque,
developed power . ii) Repeat with Nm= 1500 rpm. Assume same
Ia.
Solution on Greenboard
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Speed Control of Separately Excited
DC Motor
By Controlling(reducing)Field CurrentIf or and keepingVtat rated
value. This method of speed control is applicable
for speeds above rated speed.
m
T1
T2T3
T12>3
2
3
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A separately excited dc motor with negligible armature
resistanceoperates at 1800 rpm under no-load with Vt=240V(rated
voltage).
The rated speed of the motor is 1750 rpm.
i) Determine Vtif the motor has to operate at 1200 rpm under
no-load.
ii) Determine
(flux/pole) if the motor has to operate at 2400 rpmunder
no-load; given that K = 400/.
iii) Determine the rated flux per pole of the machine.
Separately excited dc motorExample 2
Solution on Greenboard
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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
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+
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Losses in dc machines
