Theory of Electrical Machines EXIT Course Title: Theory of Electrical Machines Course Code: EE 359...
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Transcript of Theory of Electrical Machines EXIT Course Title: Theory of Electrical Machines Course Code: EE 359...
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Course Title: Theory of Electrical Machines
Course Code: EE 359
Topic : D C Machines
Branch: ME Semester: V
Text Books:1.S. Chapman, Electric Machinery Fundamentals, 4th Ed., McGraw-Hill, 2003.2.R. K. Rajput, Electrical Machines, 3rd Ed., Laxmi Publications (P) Ltd., 2003
Theory of Electrical MachinesTheory of Electrical Machines EXIT
D.C Machine1.Introduction
2.Construction
3.Principle of Operation
4.Types of DC Machines
5.Characteristics
6.Applications
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINESDC MACHINES
INTODUCTIONINTODUCTION
A DC machine is an electro-mechanical energy conversion device. It can convert Mechanical power into Electrical Power. When output electrical power is DC , it is called DC Generator. When it converts DC electrical power into mechanical power , it is known as DC Motor.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
3. FIELD or EXCITING COILS
1. BODY OR MAGNETIC FRAME OR YOKE
2. POLE CORE AND POLE SHOES
4. ARMATURE CORE
5. ARMATURE WINDING
6. COMMUTATOR
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
9. BEARINGS
7. BRUSHES
8. END HOUSINGS
10. SHAFT
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
Body / Yoke
Field Winding
Shaft
Commutator Armature
PulleyBrush
Brushholder
Field Core
Bearing
End Housing
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
+
-
YOKEARMATURE
COMMUTATOR
SHAFT
BRUSHFIELD POLE
& COIL
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
The outer cylindrical frame to which main poles and inter poles are fixed and by means of the machine is fixed to the foundation is called YOKE.
1. MAGNETIC FRAME or YOKE :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
It serves two purposes:
a) It provides
mechanical protection
to the inner parts of the
machines.
1. MAGNETIC FRAME or YOKE :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
b) It provides a low
reluctance path for the
magnetic flux.
The yoke is made of
cast iron for smaller …
1. MAGNETIC FRAME or YOKE :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
machines and cast steel
or fabricated rolled
steel for larger
machines.
1. MAGNETIC FRAME or YOKE :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
The pole core and pole shoes are fixed to the yoke by bolts. They serves the following purpose :
a) They support the field or exciting coils.
2. POLE CORE AND POLE SHOES :
POLE CORE
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
b) They distribute the magnetic flux on the armature periphery more uniformly.
2. POLE CORE AND POLE SHOES :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
c) The pole shoes have
larger X- section, so,
the reluctance of the
magnetic path is
reduced. The pole core
2. POLE CORE AND POLE SHOES :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
and pole shoes are
made of laminated
steel assembled by
riveting together under
hydraulic pressure.
2. POLE CORE AND POLE SHOES :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
Field coils or exciting coils are used to magnetise the pole core. Enameled copper wire is used for the construction of these coils.When direct
3. FIELD or EXCITING COILS :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
current is passed through these coils/ winding, it sets up the magnetic field which magnetise the pole core to the reqd. flux.
3. FIELD or EXCITING COILS :
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
Armature is a rotating part of the DC
machine, reversal of flux takes place,
so hysteresis losses are produced.
To minimise this loss, silicon steel is
used for the construction.
4. ARMATURE CORE:
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
The rotating armature cuts the main
magnetic field , therefore an e.m.f is
induced in the armature core.This e.m.f
circulates eddy currents in the core
which results in eddy current loss in it.
4. ARMATURE CORE:
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
The armature core is laminated to reduce
the eddy current loss.Armature core serves the following purposes:a) It houses the conductors in the slots.b) It provides an easy path for magnetic flux
4. ARMATURE CORE:
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
The no. of conductors in form of coils placed in the slots of the armature and suitably inter connected are called winding .
5. ARMATURE WINDING ;
ARMATURE WINDING
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
This is the
armature winding
where conversion
of power takes
place i.e. in case
of generator ,
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
mechanical power
is converted into
electrical power
and in case of a
motor, electrical
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
power is
converted into
mechanical
power.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
Depending upon the types of inter connection. of coils , the winding can be classified into two types;i) Lap Winding;
The conductors/coils are connected in such a way that no of parallel paths are equal to no. of poles.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
If machine has ‘P’ no. of poles and ‘Z’ no. of conductors, then there will be ‘P’ no. of parallel paths.And each path will have ‘Z/P’ no of conductors in series. Also the no. of brushes are equal to no. of parallel paths.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
Out of which half of the brushes will be positive and remaining will be negative.ii) Wave Winding;
The conductors are so connected that they are divided into two parallel paths only , irrespective of the no. of poles. If machines has ‘Z’ no. of …
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
5. ARMATURE WINDING ;
conductors, there will be only two parallel paths and each will be having ‘Z/2’ no. of conductors connected in series with only two brushes.
Click here to study detailed contents of winding
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
It is the most important part of a DC machine and serves the following purpose :- i) It connects …
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
the rotating armature conductors to the stationary external circuit through the brushes.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
ii) It converts altering current induced in the armature conductors into unidirectional …..
COMMUTATOR
6. COMMUTATOR
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
current in the external load circuit in generating action and it converts alternating torque into unidirectional
COMMUTATOR
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR COPPER SEGMENTRISER
END RING
ADJUSTING NUT
METAL SLEEVESHAFT
MICA INSULATION
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
torque produced in the armature in motoring action. The commutator is of cylindrical shape and is made of wedge shaped hard drawn copper segments.The segments are insulated from each ….
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
6. COMMUTATOR
other by a thin sheet of mica.The segments are held together by means of two V-shaped rings that fit into the V-grooves cut into the segments. Each armature coil is connected to the commutator segment through riser.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
7. BRUSHES
Brushes are made of high grade carbon.They form the connecting link between armature winding and the external circuit. The brushes are held in particular position around the commutator by brush holders.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
8. END HOUSINGS
They are attached to the ends of main frame and support bearing . The front housing supports …..
END HOUSING
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
8. END HOUSINGS
the bearing and the brush assembly whereas rear housing supports the bearing only.
END HOUSING
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
9. BEARINGS
The function of the bearing is to reduce
friction between the rotating and
stationary parts of the machines.These
are fitted in the end housings.
Generally, high carbon steel is used for
the construction of the bearings.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
10. SHAFT
The function of
shaft is to transfer
mechanical power
to the machine or
from the machine . SHAFT
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
Shaft is made of
mild steel with
maximum breaking
strength. All the
rotating parts likeSHAFT
10. SHAFT
Theory of Electrical MachinesTheory of Electrical Machines EXIT
MAIN CONSTRUCTIONAL FEATURES
LECTURE 7 OF 40
DC MACHINESDC MACHINES
MAIN CONSTRUCTIONAL FEATURESMAIN CONSTRUCTIONAL FEATURES
Armature
core, ,commutator,
cooling fan etc. are keyed
to the shaft.
SHAFT
10. SHAFT
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Principle of OperationPrinciple of Operation
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Fig. 1
DC MACHINES
+ +
+
FIELDPOLES N
SFIELD
WINDING
ARMATURE CONDUCTORS
ARMATURE
YOKE
BRUSH
MAIN FIELD AXIS
BRUSH AXIS + _
++
++
.
.
.
.
+ +
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The field windings are shown as
excited from external source. The
polarity of electro-magnetic field will
depend upon the direction of field
current as shown in the fig.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Fig. 2
DC MACHINES
N
S
Te
A B_
+
S N
TL
MECHANIC
AL LO
AD
( MOTOR )
vDCSUPPLY
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION CONCEPT OF ALIGNMENT OF TWO MAGNETIC FIELDS
DC MACHINES
The armature carries conductors in
side the slots.Two brushes are placed
at the right angle to the main field axis.
The brushes are stationary whereas
armature is free to rotate.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION CONCEPT OF ALIGNMENT OF TWO MAGNETIC FIELDS
DC MACHINES
When the armature is rotated in the
magnetic field, an e.m.f will be induced
in the armature conductors.The
direction of the induced e.m.f can be
found by applying Fleming’s Right
Hand Rule.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The direction of induced e.m.f will depend upon the direction of rotation of armature , if polarity of field poles to be kept unchanged.When load is connected across the armature terminals , the current will flow through the armature circuit.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The direction of current will be same as that of induced e.m.f. The armature will now be considered as electro-magnet and its polarity is shown in the fig. 2 .The electro-magnetic torque Te will be developed in the anti-clock wise direction as shown in the fig. no. 1 and 2.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The magnitude of Te will depend on the
strength of the field poles and armature field which further depends upon the currents flowing through the respective windings. As the external load on the generator is increased, the magnitude of Te increases.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
As Te acts in the opposite direction to
the applied mechanical torque, more
torque will be required through the
prime mover to maintain the speed of
armature .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The direction of currents in the upper
conductors in the armature are
indicated by ‘dots’ and conductors in
lower half of armature are indicated by
‘cross’ .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The brush ‘B’ will collect dot currents
and brush ‘A’ will collect cross
currents as the armature continues to
rotate in clockwise direction. In the out
put circuit, across terminals ‘A’ and ‘B’,
current will flow in one direction.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The dc machine shown in fig. 2 is
working as Generator. The same
machine will work as motor , if the
armature is provided with electric
supply as shown in fig. 3.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Fig 3
DC MACHINES
N
S
Te
A B_
+
S N
( GENERATOR )
ELECTRICALLOAD
Tm
ME
CH
AN
ICA
L INP
UT
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The armature is connected across a
supply voltage ‘V’ and the field
windings are excited from the same
supply or from any external dc source.
The magnetic polarities due to the
current in armature winding will be as
shown in fig.3.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
The electro-magnetic torque Te will be
developed in the anti-clockwise
direction as opposite poles of armature
field and main field will attract each
other. The armature will rotate in anti-
clockwise direction due to Te .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
To reverse the direction of rotation of armature, either the direction of current in the field winding or armature winding will have to be reversed.If the direction of currents in both the windings are reversed, direction of rotation of armature will be unchanged.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DC MACHINES
As the mechanical load on the armature i.e. rotor shaft represented by load torque TL is increased, more and more electro-magnetic torque will be developed by the armature to balance the mechanical torque requirements for which the armature will draw more current from the supply mains.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
B
Q
LOAD
A
B
AA
P
MAGNETIC FIELD
0o
Theory of Electrical MachinesTheory of Electrical Machines EXIT
B
Q
LOAD
A
BA
P
MAGNETIC FIELD
_+
e
30o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
BQ
LOAD
A
B
AP
MAGNETIC FIELD
+ _
e
60o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Q
LOAD
AB
A
MAGNETIC FIELD
B P+ _
e
90o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Q
LOAD
BA
A
A P
MAGNETIC FIELD
B
+ _
e
120o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Q
LOAD
A
B
A
AP
MAGNETIC FIELD
B
+ _
e
150o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
A
Q
LOAD
A
B
AB
P
MAGNETIC FIELD
+
e
180o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
A
Q
LOAD
A
B
B
P
MAGNETIC FIELD
+ _
e
210o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
AQ
LOAD
B
A
BP
MAGNETIC FIELD
+ _
e
240o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
Q
LOAD
BA
B
MAGNETIC FIELD
A P+ _
e
270o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
BQ
LOAD
AB
AAP
MAGNETIC FIELD
+ _
e
300o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
BQ
LOAD
B
A
AA
P
MAGNETIC FIELD
+ _
e
330o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
B
Q
LOAD
B
A
AA
P
MAGNETIC FIELD
e
360o
t
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
TYPES OF DC TYPES OF DC MachinesMachines
Depending upon the type of excitation
to the field winding. The dc machine
can be classified into three categories:
1.Machines with permanent field,
2.Separately excited
3.Self excited type
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
TYPES OF EXCITATIONS TYPES OF EXCITATIONS ( DC MOTORS )( DC MOTORS )
Dc motors with permanent magnetic
field, are manufactured for small rating
applications such as toys, cassette tape
recorders etc.large rating dc motors …
Theory of Electrical MachinesTheory of Electrical Machines EXIT
TYPES OF EXCITATIONS TYPES OF EXCITATIONS ( DC MOTORS )( DC MOTORS )
are constructed with electro-magnetic
field i.e field winding is placed on the
field core and this winding is supplied
with dc current called excitation.
Depending upon the type of
connections to the field winding for ….
Theory of Electrical MachinesTheory of Electrical Machines EXIT
TYPES OF TYPES OF DC MOTORS DC MOTORS
The dc motors can be classified into
two categories ;
1) Separately excited dc motors
2) Self excited dc motors.
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
Theory of Electrical MachinesTheory of Electrical Machines EXIT
SEPARATELY EXCITED DC MOTORSSEPARATELY EXCITED DC MOTORS
A
AA
ERa
Ia
V
+
_VDC
If
+ _
F FF
+
_
MSupply
Rf
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
Theory of Electrical MachinesTheory of Electrical Machines EXIT
• The field winding is excited from a
supply which is not connected to the
armature winding. It may be noted
that current flowing through the field
winding is independent of load and
is equal to V / Rf , where Rf is the….
SEPARATELY EXCITED DC MOTORSSEPARATELY EXCITED DC MOTORS
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
Theory of Electrical MachinesTheory of Electrical Machines EXIT
field circuit resistance. The flux
produced is proportional to the field
current i.e. Ø If
SEPARATELY EXCITED DC MOTORSSEPARATELY EXCITED DC MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SUPPLYERa
IL
V
FF
IfIa
AA
+
_
F
M
A
SELF EXCITED DC MOTORS ( DC SHUNT MOTORS )SELF EXCITED DC MOTORS ( DC SHUNT MOTORS )
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC SHUNT MOTORS )( DC SHUNT MOTORS )
In this type of excitation , armature and
field windings are connected across a
constant source of supply. The field
current If is drawn from the same
source as that of armature current. As
shown in fig.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
SELF EXCITED DC MOTORS ( DC SERIES MOTORS )SELF EXCITED DC MOTORS ( DC SERIES MOTORS )
A
ERa
IL
V
+
_
Ia
AA
ISE
YYY+
_
M SUPPLY
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
The field winding is connected in
series with the armature so that If = Ia =
IL . Therefore field winding is made up
of thick winding wire of less no. of
turns as compared to that of shunt field
winding so that armature current can ...
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC SERIES MOTORS )( DC SERIES MOTORS )
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
flow through it without overheating. In
case of dc series machine , Ø If Ia ..
The relationship between induced
e.m.f. and terminal voltage is as follows
; …..See Fig.
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC SERIES MOTORS )( DC SERIES MOTORS )
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
V = E + Ia Ra + Ia Rse
orE = V - Ia ( Ra + Rse )
Ia = Ise = ILand
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC SERIES MOTORS )( DC SERIES MOTORS )
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )
A
ERa
IL
V
Ia
AA
ISE
YYY+
_
ISh
Z
ZZ
RshSUPPLY
M
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
There are two field windings , namely a
shunt field winding and a series field
winding. The shunt field winding is
connected in parallel with the armature
and series field winding is connected
in series with the combination .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
Series field winding will carry a large
armature current Ia or IL and therefore it
is made of wire of large cross section
and has a few turns only. The
resistance of series field winding is
very small.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
The shunt field winding is made up of
wires of small cross section and has
high resistance. Since the resistance of
shunt field winding is high , the current
flowing through it is very small as
compared to that of series field
winding
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
or armature current Ia . The main
magnetic field flux is produced by the
shunt field current / winding but it is
modified by the field of series winding.
A compound machine therefore
combines the best features of dc
shunt machines and dc series
machines.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
Depending up on the connections of
shunt field winding in the combination
of armature and series field winding, dc
compound generators can be named
as
i) Short shunt compound generators.
ii) Long shunt compound generators.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SHORT SHUNT TYPE ( DC COMPOUND MOTORS )SHORT SHUNT TYPE ( DC COMPOUND MOTORS )
A
ERa
IL
V
Ia
AA
ISE
YYY+
_
ISh
Z
ZZ
RshSUPPLY
M
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SHORT SHUNT TYPE SHORT SHUNT TYPE ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
In this case the shunt field winding is
connected across the armature winding
only as shown in the fig of slide no.
i) SHORT SHUNT DC COMPOUND MOTORS
Ise = IL = Ia + Ish
V = E + Ia Ra+ Ise Rse
= E + Ia Ra+ ( Ia + Ish ) Rse
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
LONG SHUNT TYPE ( DC COMPOUND MOTORS )LONG SHUNT TYPE ( DC COMPOUND MOTORS )
A
ERa
IL
V
Ia
AA
ISE
YYY+
_
ISh
Z
ZZ
RshSUPPLY
M
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
LONG SHUNT TYPE LONG SHUNT TYPE ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
In this case the shunt field winding is
connected across the combination of
armature and series field winding as
shown in the fig. Ise = Ia and IL= Ia + Ish
V = E + Ia Ra+ Ise Rse
= Ish Rsh
ii) LONG SHUNT DC COMPOUND MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
SELF EXCITED DC MOTORS SELF EXCITED DC MOTORS ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
Depending upon the direction of flow of
current through series field, we can
classify dc compound motors into two
categories namely ;
I) Cumulative compound dc motors
II) differential compound dc motors
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
CUMULATIVE TYPE ( DC COMPOUND MOTORS )CUMULATIVE TYPE ( DC COMPOUND MOTORS )
A
ERa
IL
V
Ia
AA
ISE
YYY+
_
ISh
Z
ZZ
RshSUPPLY
M
Ø = Øsh + Øse
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
CUMULATIVE TYPE CUMULATIVE TYPE ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
The direction of current in the series
field winding is such that magnetic field
produced by it is in the direction to that
of shunt field. Total magnitude of the
field is the sum of shunt field and series
field so that Ø = Øsh + Øse. .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENTIAL TYPE ( DC COMPOUND MOTORS )DIFFERENTIAL TYPE ( DC COMPOUND MOTORS )
A
ERa
IL
V
Ia
AA
ISE
YYY +
_
ISh
Z
ZZ
RshSUPPLY
M
Ø = Øsh - Øse
Theory of Electrical MachinesTheory of Electrical Machines EXIT
DIFFERENT TYPES OF EXCITATIONS ( DC MOTORS )
DIFFERENTIAL TYPE DIFFERENTIAL TYPE ( DC COMPOUND MOTORS )( DC COMPOUND MOTORS )
The direction of current in the series
field winding is such that magnetic field
produced by it is in the opposite
direction to that of shunt field. Total
magnitude of the field is the difference
of shunt field and series field so that
Ø = Øsh - Øse.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
FACTORS DETERMINING THE SPEED OF DC MOTOR
FACTORS DETERMINING THE SPEED OF DC MOTORFACTORS DETERMINING THE SPEED OF DC MOTOR
The expression for back e.m.f.
developed in the armature of a dc motor
is given as follows :
P Ø Z N 60 A
E = …..(i)
E = V - Ia Ra …..(ii)
Theory of Electrical MachinesTheory of Electrical Machines EXIT
FACTORS DETERMINING THE SPEED OF DC MOTORFACTORS DETERMINING THE SPEED OF DC MOTOR
P Ø Z N 60 A
= V - Ia Ra
Comparing expressions (i) and (ii)
K Ø N = V - Ia Ra OR
N = V - Ia Ra
K Ø
Theory of Electrical MachinesTheory of Electrical Machines EXIT
FACTORS DETERMINING THE SPEED OF DC MOTOR
FACTORS DETERMINING THE SPEED OF DC MOTORFACTORS DETERMINING THE SPEED OF DC MOTOR
Where K is the constant of
proportionality and equal to PZ / 60 A
Now in the above expression for speed,
the speed can be varied by varying the
applied voltage ‘V’ , field flux Ø and
resistance of the armature .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
FACTORS DETERMINING THE SPEED OF DC MOTOR
FACTORS DETERMINING THE SPEED OF DC MOTORFACTORS DETERMINING THE SPEED OF DC MOTOR
It is clear that speed is directly
proportional to the supply voltage ‘V’. So
the speed increases with increase in
voltage ‘V’ and vice versa.
The speed is inversely proportional to
the field flux Ø . So speed decreases as
the Flux Ø increases and vice versa.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
The important characteristics of dc
motors are :
1) Speed - armature current ( Load )
characteristics
2) Torque - armature current ( Load )
characteristics
3) Speed - Torque characteristics
CHARACTERISTICS OF CHARACTERISTICS OF DC MOTORSDC MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
It is very much important to know the
characteristics mentioned above for
different types of dc motors because it
enables the selection of a specific type
of dc motor for specific purpose.
CHARACTERISTICS OF CHARACTERISTICS OF DC MOTORSDC MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC SHUNT MOTORSCHARACTERISTICS OF DC SHUNT MOTORS
SUPPLYERa
IL
V
FF
IfIa
AA
+
_
F
M
A
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC SHUNT MOTORSCHARACTERISTICS OF DC SHUNT MOTORS
N
Ia
FULL LOAD
0( Amps)
Theory of Electrical MachinesTheory of Electrical Machines EXIT
CHARACTERISTICS OF DC SHUNT MOTORSCHARACTERISTICS OF DC SHUNT MOTORS
For a dc motor , we know that ;
N = V - Ia Ra
K Ø
A dc shunt motor is connected across
the mains having supply voltage ‘V’ .
N
Ia
FULL LOAD
0( Amps)
1. Speed - Armature current (Load ) characteristics
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SHUNT MOTORSDC SHUNT MOTORS
This supply voltage is assumed to be
constant.The field winding is connected
across the armature as shown in Fig.
The magnetic flux Ø produced by field
current If will be constant as V remains
constant.
Speed - Armature current (Load ) characteristics
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SHUNT MOTORSDC SHUNT MOTORS
1. Speed - Armature current (Load ) characteristics
But in actual practice, the air gap flux is
slightly reduced due to the effect of
armature reaction. From the expression
for the speed mentioned earlier, it is
evident that as the armature current Ia …...
Theory of Electrical MachinesTheory of Electrical Machines EXIT
CHARACTERISTICS OF CHARACTERISTICS OF DC SHUNT MOTORSDC SHUNT MOTORS
increases , speed will decrease by a
small amount due to an increase in Ia Ra
drop is very small as compared to V .
The speed verses armature current
characteristics is shown in Fig.
1. Speed - Armature current (Load ) characteristics
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SHUNT MOTORSDC SHUNT MOTORS
The shunt motor being thus more or less
a constant speed motor , can be used in
the applications such as driving of line
shafts, lathes conveyors etc.
1. Speed - Armature current (Load ) characteristics
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC SHUNT MOTORSCHARACTERISTICS OF DC SHUNT MOTORS
T
Ia
0( Amps)
2. Torque - Armature current (Load ) characteristics
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SHUNT MOTORSDC SHUNT MOTORS
2. Torque - Armature current (Load ) characteristics
The equation for torque can be written as
follows ; T = kt Ø Ia
If flux Ø is taken as constant, the torque
T becomes directly proportional to
armature current (Load current) Ia . It is a
straight line passing through the origin.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SHUNT MOTORSDC SHUNT MOTORS
N
T0
( N-m)
3. Speed - Torque characteristics
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SHUNT MOTORSDC SHUNT MOTORS
3. Speed - Torque characteristics
And The relationship between speed and torque can be drawn as shown in Fig .
N = V - Ia Ra
K Ø
The relation between T and Ia and N
and Ia are as under ;T = kt Ø Ia
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
A
ERa
IL
V
+
_
Ia
AA
ISE
YYY+
_
M SUPPLY
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SERIES MOTORSDC SERIES MOTORS
1. Speed - Load characteristics
N
0Ia ( Amps)
Theory of Electrical MachinesTheory of Electrical Machines EXIT
CHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
1. Speed - Load characteristics
From the expression ; N = V - Ia Ra
K Ø
It is seen that the speed N is inversely
proportional to flux Ø
For a dc series motor ,magnetic flux Ø is
proportional to Ia.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF CHARACTERISTICS OF DC SERIES MOTORSDC SERIES MOTORS
1. Speed - Load characteristics
Thus , if V is constant, N is inversely
proportional to Ia. The N verses Ia
characteristics is therefore a rectangular
hyperbola as shown in Fig . It is seen
from the characteristics that ….
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Speed - Load characteristics
the speed decreases as the load on the
motor increases. At a very low load , the
speed is dangerously high . Thus if a dc
series motor is allowed to run on very
light load or at No- Load , its speed will
become much higher than its ……..
CHARACTERISTICS OF CHARACTERISTICS OF DC SERIES MOTORSDC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Speed - Load characteristics
normal speed which may cause damage
to the motor. For this reason , dc series
motors are never started on No- Load
and are not used in the applications
where there is a chance of Load being
completely removed , when the motor ...
CHARACTERISTICS OF CHARACTERISTICS OF DC SERIES MOTORSDC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Speed - Load characteristics
remains connected to the supply. The
load on the dc series motor is connected
through the gears and not through the
belt pulley arrangement.This is because,
in case of failure of belt , the load will be
removed from the motor and thereby the
CHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Speed - Load characteristics
motor will attain a dangerously high
speed . In case of load connected
through the gears, however in the event
of an accidental release of load, gears
will provide some load on account of the
frictional resistance of the gear teeth.
CHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Load characteristics
T
0Ia ( Amps)
SATURATION OF SERIES FIELD CORE
CHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Load characteristics
The equation for the torque for dc motor
is given by ; T = kt Ø Ia
The magnetic flux for a dc series motor is
proportional to armature current Ia. Thus
the torque T = kt Ia Ia.
Or T Ia2
CHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Load characteristicsCHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
The relationship between torque and
armature current , is therefore of the form
of a parabola . With increase in Ia , the
field flux increases linearly but due to
saturation of the core, beyond a certain
magnitude of Ia the increase in flux is
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Load characteristicsCHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
negligible.. Thus T is proportional to the
square of Ia up to the saturation point
beyond which T varies linearly with Ia.
From the torque load characteristics , it
can be observed that a dc series motor ..
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Load characteristicsCHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
started on-load , develops a very high
starting torque.
Hence dc series motors are used in
applications where high starting torque
is required such as in electric trains ,
hoists, trolleys etc.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Speed characteristicsCHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
T0
N
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Speed characteristicsCHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
From the characteristics shown in slide
no. , it can be seen that for low speeds ,
the torque is high and for high speeds
the torque is very small. This is why dc
series motor is widely used in the … ..
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Torque - Speed characteristicsCHARACTERISTICS OF DC SERIES MOTORSCHARACTERISTICS OF DC SERIES MOTORS
applications where motor is to be started
on bulk loads such as electric loco-
motive.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
A
ERa
IL
V
Ia
AA
ISE
YYY+
_
ISh
Z
ZZ
RshSUPPLY
M
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
1. Speed - Load characteristicsCHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
0
N
Ia ( Amps)
DIFFERENTIALCOMPOUND
SHUNT
CUMULATIVECOMPOUND
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
1. Speed - Load characteristics
In cumulative compound motors , series
field winding is connected in such a way
that magnetic flux produced by it helps
the flux produced by shunt field winding.
Series field is directly proportional to the
load current , ….. . … .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
1. Speed - Load characteristics
therefore total flux increases with
increase in load current / armature
current due to the series field in addition
to the voltage drop in the armature
winding.The speed of dc motor is
inversely proportional to the . .. . ..
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
1. Speed - Load characteristics
total main flux Ø . Therefore speed drops
more sharply as compared to dc shunt
motor.Refer Fig.
See Fig.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics
T
0Ia ( Amps)
DIFFERENTIALCOMPOUND
SHUNTCUMULATIVECOMPOUND
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics
The torque developed by a cumulative
compound motor increases with sudden
increase in load and at no-load , it has a
definite speed. Cumulative compound
motors are therefore, suitable where
there is sudden application . . . . . . .
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics
of heavy loads like sheers, punches,
rolling mills etc. The speed of differential
compound motors remains more or less
constant. With increase in load but its
torque decreases with load. Since the dc
shunt motor develops a good torque and
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
2. Torque - Load characteristics
its speed does not vary appreciably with
increase in load, differential compound
motors are not preferred over dc shunt
motors and hence are rarely used.
Theory of Electrical MachinesTheory of Electrical Machines EXIT
PERFORMANCE AND CHARACTERISTICS OF DC MOTORS
CHARACTERISTICS OF DC COMPOUND MOTORSCHARACTERISTICS OF DC COMPOUND MOTORS
3. Speed - Torque characteristics
0
N
T (N-m)
DIFFERENTIALCOMPOUND
CUMULATIVECOMPOUND
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
(i) Shunt motors are used in situations, such as driving a line shafting etc. where the speed as to be maintained approximately constant between no-load and full-load.
APPLICATIONS OF DC MOTORS
(a) DC SHUNT MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
(ii) In situations where variable load is to be driven at different speeds but at each load, the speed is to be kept constant. Such as driving a lathe.
APPLICATIONS OF DC MOTORS
(a) DC SHUNT MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
DC Series Motors are used in applications such as driving hoists, cranes, trains, etc., as in these cases a large starting torque is required. They are also used where the motor can be permanently coupled to the load, such as
APPLICATIONS OF DC MOTORS
(b) DC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
Fans , whose torque increases with speed. Where constancy in speed is not essential, the decrease of speed with increase of load has the advantage that the power absorbed by the motor does not increase as rapidly as the torque .
APPLICATIONS OF DC MOTORS
(b) DC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
Series motors acquire very high speed at no-load or at very light load . That is why they should not be used for a belt drive where there is a possibility of the load decreasing to very small value.
APPLICATIONS OF DC MOTORS
(b) DC SERIES MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
DC Compound Motors are used in application where large starting torque are required but where the load may fall to such a small value that a series motor would reach a dangerously high speed.
APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
Where the supply voltage may fluctuate , for instance on a traction system, the series winding reduces the fluctuation of armature current partly by its inductance and partly by its influence on the value of
APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
flux and therefore on that of the induced e.m.f.
When the load is of a fluctuating nature , e.g. for driving stamping processes, etc. the shunt excitation prevents the speed …
APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
Becoming excessive on light load, and the decrease of speed with increase of load enables the flywheel, usually fitted to such a machine, to assist the motor in in dealing with the peak load by giving
APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
Theory of Electrical MachinesTheory of Electrical Machines EXIT
APPLICATION OF DC MACHINES
up some of its kinetic energy.
APPLICATIONS OF DC MOTORS
(c) DC COMPOUND MOTORS
* THANKS *