DC Machine_session 2 out of four sessions
haripriyakulkarni4
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May 27, 2024
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About This Presentation
DC Machine_session 2 out of four sessions
Slide Content
Electrical Machines-1
Unit 3: DCMachines
Dr.Mrs. Haripriya H. Kulkarni.
Unit 3: DCMachines
Dr.Mrs. Haripriya H. Kulkarni.
Review of previous Lecture
•Transformer-1 phase and 3 phase
•Transformer-1 phase and 3 phase
Learning Objectives
Comparison between Motor and Generator
Study of D.C. Machine
Basics of Machine
Operating principle of Motor and Generator
Different parts and its function
Comparison between Motor and Generator
Study of D.C. Machine
Basics of Machine
Operating principle of Motor and Generator
Different parts and its function
Learning Outcomes
Students will be able to :
Compare Motor and Generator
Study of D.C. Machine
Explain basics of Machine
Demonstrate operating principle of Motor and Generator
Different parts and its function
Students will be able to :
Compare Motor and Generator
Study of D.C. Machine
Explain basics of Machine
Demonstrate operating principle of Motor and Generator
Different parts and its function
Generating and Motoring Action
DIFFERENCE BETWEEN MOTOR AND GENERATOR
+
MOTOR GENERATOR
DIFFERENCE BETWEEN MOTOR AND GENERATOR
+
MOTOR GENERATOR
BASIS MOTOR GENERATOR
Function The Motor converts Electrical energy into
Mechanical energy
The Generator converts Mechanical energy to
Electrical Energy
Electricity It uses electricity. It generates electricity
Driven
element
The Shaft of the motor is driven by the
magnetic force developed between
armature and field.
The Shaft is attached to the rotor and is driven
by mechanical force.
Current Current is to be supplied to the armature
of the motor
In the generator current is produced in the
armature windings.
Rule
Followed
Motor follows Fleming·s Left hand rule. GeneratorfollowsFlcming's Right hand rule.
Example An electric car or bike is an example
of electric motor.
Energy in the form of electricity is generated at
the power stations.
Generating and Motoring Action
Function The Motor converts Electrical energy into
Mechanical energy
The Generator converts Mechanical energy to
Electrical Energy
Electricity It uses electricity. It generates electricity
Driven
element
The Shaft of the motor is driven by the
magnetic force developed between
armature and field.
The Shaft is attached to the rotor and is driven
by mechanical force.
Current Current is to be supplied to the armature
of the motor
In the generator current is produced in the
armature windings.
Rule
Followed
Motor follows Fleming·s Left hand rule. GeneratorfollowsFlcming's Right hand rule.
Example An electric car or bike is an example
of electric motor.
Energy in the form of electricity is generated at
the power stations.
Generating and Motoring Action
Left Hand-Motor
principle
Right Hand-
Generator principle
principle
Right Hand-
Generator principle
DC Generator Construction
A DC Generator is an electrical device which converts mechanical energy intoelectrical energy.
libdkiH:IHI
Itmainlyconsists of three main pa1ts,i.e.magneticfieldsystem,armatm-eandcommutator andbrush gear.
The other partsofa DCGenerator are magnetic fn1n1e and yoke, pole coreand poleshoes, field orexciting
coils, armature core and windings, brushes, end housings, bea,ings andshafts.
A DC Generator is an electrical device which converts mechanical energy intoelectrical energy.
libdkiH:IHI
Itmainlyconsists of three main pa1ts,i.e.magneticfieldsystem,armatm-eandcommutator andbrush gear.
The other partsofa DCGenerator are magnetic fn1n1e and yoke, pole coreand poleshoes, field orexciting
coils, armature core and windings, brushes, end housings, bea,ings andshafts.
DC Generator Construction
Arm;nure
CommuUitor
8ru hi,s
Arm;nure
CommuUitor
8ru hi,s
DC Generator Construction
-
Field winding/ Pole coils:
They are usually made ofcopper.
Field coils are former wound and placed on each
pole and are connected inseries.
They are wound in such a way that, when energized,
they form alternate North and South poles.
-
Field winding/ Pole coils:
They are usually made ofcopper.
Field coils are former wound and placed on each
pole and are connected inseries.
They are wound in such a way that, when energized,
they form alternate North and South poles.
DC Generator Construction
Pole s h o e s function:
Poles arejoined to the yoke with the help of bolts or welding.
It carries and support the field winding.
To support the filed winding: Pole Core provides this area to
wound the field winding.
To spread out the flux in air gap:Pole core direct the magnetic flux
to the air gap, armature, and to the next pole.
0
Pole s h o e s function:
Poles arejoined to the yoke with the help of bolts or welding.
It carries and support the field winding.
To support the filed winding: Pole Core provides this area to
wound the field winding.
To spread out the flux in air gap:Pole core direct the magnetic flux
to the air gap, armature, and to the next pole.
0
DC Generator Construction
Armature core/ rotor:
Armature core is the rotor of a de machine.
It is cylintlrical in shape with slots tocarryarmature winding.
11,e armature is built up of thin luminated circular steel disks for reducing eddy current losses.
It may be provided with air ducts for the axialair flow for cooling purposes.
Armature is keyed to theshaft.
Armature core/ rotor:
Armature core is the rotor of a de machine.
It is cylintlrical in shape with slots tocarryarmature winding.
11,e armature is built up of thin luminated circular steel disks for reducing eddy current losses.
It may be provided with air ducts for the axialair flow for cooling purposes.
Armature is keyed to theshaft.
DC Generator Construction
Armatvr• Windmgl
Armature winding:
The armature core slots are mainly used for holding the armature winding and it is connected in series
to parallel for enhancing the sum of produced current.
Armatvr• Windmgl
Armature winding:
The armature core slots are mainly used for holding the armature winding and it is connected in series
to parallel for enhancing the sum of produced current.
DC Generator Construction
Commutator:
The working of the commutator is like a rectifier for changing AC voltage to the DC voltage within the
armature ,winding to across the brushes.
It is designed ,with a copper segment, and each copper segment is protected from each other,with the
help of mica sheets. It is located on the shaft of the machine.
Commutator:
The working of the commutator is like a rectifier for changing AC voltage to the DC voltage within the
armature ,winding to across the brushes.
It is designed ,with a copper segment, and each copper segment is protected from each other,with the
help of mica sheets. It is located on the shaft of the machine.
DC Generator Construction
Brushes:
The electrical connections can be ensured between the commutator as well as the external load circuit
with the help of brushes
They collect current from commutator. Made up of carbon or graphite.
Brushes:
The electrical connections can be ensured between the commutator as well as the external load circuit
with the help of brushes
They collect current from commutator. Made up of carbon or graphite.
Student’s Evaluation
Name the parts of D.C.Machine
Flemings left hand rule? Application?
Flemings right hand rule? Application?
Name the parts of D.C.Machine
Flemings left hand rule? Application?
Flemings right hand rule? Application?
Assignment
1. Draw constructional diagram of D.C. machine. State functions of different parts along with
the material used.
1. Draw constructional diagram of D.C. machine. State functions of different parts along with
the material used.
Wrap up
1. Principle of operation of D.C. Machine
2. As a motor, as a generator
3. Different parts of machine
4. Function of each part and construction , significance.
1. Principle of operation of D.C. Machine
2. As a motor, as a generator
3. Different parts of machine
4. Function of each part and construction , significance.
DC Generator Construction_ (Draw in exam)
Commutator
Brushes
Commutator
Brushes
Sr. No. Name of part Material Used Function
l. Yoke cast iron (small
generators) or cast
or rolled steel Oarge
size generators).
. main coverof the DCGenerator
. actsas protecting shield for generator
. provides a mechanical support for the poles.
. It also carries the magnetic flux produced by the
poles.
.
2. Field winding
/pole coils
Copper
Each pole core has one or more field coils (windings)
.
placed over it to produce a magnetic field.
Field coils are former wound and placed on each pole
.
and are connected inseries.
They are wound in such a way that, when energized,
they form alternate North and South poles.
3. Pole shoes 111in cast steel or
wrought iron
Jnminations which
are riveted together
under hydraulic
pressure
Poles are joined to the yoke with the help of bolts or
.
welding.
.
It carries andsupport the field winding.
Tosupport the filedwinding: PoleCore provides this
.
area to wound the fieldwinding.
Tospread out the flux in air gap: Pole core direct the
magnetic f i l L through the air gap, armature, and to the
next pole.
DCGenerator Construction_ InShort
l. Yoke cast iron (small
generators) or cast
or rolled steel Oarge
size generators).
. main coverof the DCGenerator
. actsas protecting shield for generator
. provides a mechanical support for the poles.
. It also carries the magnetic flux produced by the
poles.
.
2. Field winding
/pole coils
Copper
Each pole core has one or more field coils (windings)
.
placed over it to produce a magnetic field.
Field coils are former wound and placed on each pole
.
and are connected inseries.
They are wound in such a way that, when energized,
they form alternate North and South poles.
3. Pole shoes 111in cast steel or
wrought iron
Jnminations which
are riveted together
under hydraulic
pressure
Poles are joined to the yoke with the help of bolts or
.
welding.
.
It carries andsupport the field winding.
Tosupport the filedwinding: PoleCore provides this
.
area to wound the fieldwinding.
Tospread out the flux in air gap: Pole core direct the
magnetic f i l L through the air gap, armature, and to the
next pole.
DCGenerator Construction_ InShort
Sr. No. Name of part Material Used Function
4. Armature
core/ rotor
built up of thin
laminated circular
silicon steel disks for
reducing eddy current
losses.
Rotating part of DCmachine.
ltiscylindrical inshapewithslots to carryarmature
.
winding.
It maybeprovided with airducts for the u:ial air
flow for cooling purposes.
.
Armature is keyed to the shaft.
5. Armature
winding
Copper Hearl of the DC Machine. It is laminated to reduce
eddy current losses.
The annature core slots are mainly used for holding
thearmahtre windings.Theseare in a closed circuit
winding form, and it is -onnected in se1ics to parallel
for enhancing the sum of produced current.
6. Commutator Made from a number
of wedge-shaped hard
drawn copper bars or
segments insulated
from each other and
from theshaft.
It islikearectifier for cbangingACvoltageto tlte
DCvoltage within the armature winding to across the
.
brnshes.
It is designed with a copper segment, and each copper
segment is p1-otected from each other with the help of
mica sheets. It is located on the shaft of the machine.
DC Generator Construction
4. Armature
core/ rotor
built up of thin
laminated circular
silicon steel disks for
reducing eddy current
losses.
Rotating part of DCmachine.
ltiscylindrical inshapewithslots to carryarmature
.
winding.
It maybeprovided with airducts for the u:ial air
flow for cooling purposes.
.
Armature is keyed to the shaft.
5. Armature
winding
Copper Hearl of the DC Machine. It is laminated to reduce
eddy current losses.
The annature core slots are mainly used for holding
thearmahtre windings.Theseare in a closed circuit
winding form, and it is -onnected in se1ics to parallel
for enhancing the sum of produced current.
6. Commutator Made from a number
of wedge-shaped hard
drawn copper bars or
segments insulated
from each other and
from theshaft.
It islikearectifier for cbangingACvoltageto tlte
DCvoltage within the armature winding to across the
.
brnshes.
It is designed with a copper segment, and each copper
segment is p1-otected from each other with the help of
mica sheets. It is located on the shaft of the machine.
DC Generator Construction
Derivation of EMF Equation of a DC Machine – Generator and Motor
Let,
P – number of poles of the machine
ϕ – Flux per pole in Weber.
Z – Total number of armature conductors.
N – Speed of armature in revolution per minute (r.p.m).
A – number of parallel paths in the armature winding.
In one revolution of the armature,
the flux cut by one conductor is given as:
Let,
P – number of poles of the machine
ϕ – Flux per pole in Weber.
Z – Total number of armature conductors.
N – Speed of armature in revolution per minute (r.p.m).
A – number of parallel paths in the armature winding.
In one revolution of the armature,
the flux cut by one conductor is given as:
Therefore, the average induced e.m.f in one conductor will be:
Back emf in Motor
When the current-carrying conductor placed in a magnetic field, the torque induces on the conductor, the
torque rotates the conductor which cuts the fl,c, of the magnetic field.
According to the Electromagnetic Induction Phenomenon "when the conductor cuts the magnetic field,
EMF induces in theconductor".
The Fleming light-hand rule determines the direction of the induced EMF.
It isseen that thedirection of the induced emf is opposite tothe appliedvoltage. '111ereby theemfis
known as the counter emf or back emf.
The back emf is developed in sedes with the applied volti,ge, but OppOSite in direction, i.e., the back emf
opp05es the current which causes it.
When the current-carrying conductor placed in a magnetic field, the torque induces on the conductor, the
torque rotates the conductor which cuts the fl,c, of the magnetic field.
According to the Electromagnetic Induction Phenomenon "when the conductor cuts the magnetic field,
EMF induces in theconductor".
The Fleming light-hand rule determines the direction of the induced EMF.
It isseen that thedirection of the induced emf is opposite tothe appliedvoltage. '111ereby theemfis
known as the counter emf or back emf.
The back emf is developed in sedes with the applied volti,ge, but OppOSite in direction, i.e., the back emf
opp05es the current which causes it.
What actually Back emf in Motor does?(Significance)
Back EMF represents that portion of tl1e supply voltage which multiplied by the
current equals tl1e mechanical workproduced (roughlyspeaking).
(Therestofthesupplyvoltage is used upas1-Rclrop and produces heat - it is wasted
energy. So you really want your back EMF to be as close to the supply voltage as
possible).
The back EMF plays a self-regulating role by limiting current and energy flow
through the motor. In a parallel motor, it is only due to back EMF that if you apply a
good voltage source toan armature with a verylow resistance, whether no-load or ft
l-load, the motor would run nicelyat a near-constant speed.
Back EMF represents that portion of tl1e supply voltage which multiplied by the
current equals tl1e mechanical workproduced (roughlyspeaking).
(Therestofthesupplyvoltage is used upas1-Rclrop and produces heat - it is wasted
energy. So you really want your back EMF to be as close to the supply voltage as
possible).
The back EMF plays a self-regulating role by limiting current and energy flow
through the motor. In a parallel motor, it is only due to back EMF that if you apply a
good voltage source toan armature with a verylow resistance, whether no-load or ft
l-load, the motor would run nicelyat a near-constant speed.
Electrical and Electronics Engineering
Unit 3: DCMachines
Dr.Mrs. Haripriya H. Kulkarni.
Unit 3: DCMachines
Dr.Mrs. Haripriya H. Kulkarni.
Unit 3-Session 4
Electrical and Electronics Engineering
Unit 3: DCMachines
Electrical and Electronics Engineering
Unit 3: DCMachines
Review of previous Lecture
•Main parts of D.C. Machine, its function
and material used
•Derivation of emf equation of D.C.
Generator
•Significance of back emf
•Main parts of D.C. Machine, its function
and material used
•Derivation of emf equation of D.C.
Generator
•Significance of back emf
Learning Objectives
Types of D.C. Motors
Equations of V and I for each
Reversal of direction of motor
Types of D.C. Motors
Equations of V and I for each
Reversal of direction of motor
Learning Outcomes
Students will be able to :
Explain types of D.C. Motors
Find out the equations of V and I for each type
Change the of direction of rotation of Motor
Students will be able to :
Explain types of D.C. Motors
Find out the equations of V and I for each type
Change the of direction of rotation of Motor
TYPES OF D C MOTORS
1. D.C. Shunt Motor
Applications for these
motors vary but are
often for larger
applications such as
unwind brake
generators,
conveyors, mixers etc.
1. D.C. Shunt Motor
Applications for these
motors vary but are
often for larger
applications such as
unwind brake
generators,
conveyors, mixers etc.
TYPES OF D C MOTORS
1. D.C. Series Motor
High starting
loads such as
traction, crane
and other heavy
applications.
1. D.C. Series Motor
High starting
loads such as
traction, crane
and other heavy
applications.
TYPES OF D C MOTORS
1. D.C. Compound- Long Shunt
Applications for these
motors vary but are
often for larger
applications such as
unwind brake
generators,
conveyors, mixers etc.
1. D.C. Compound- Long Shunt
Applications for these
motors vary but are
often for larger
applications such as
unwind brake
generators,
conveyors, mixers etc.
TYPES OF D C MOTORS
1. D.C. Compound- Short Shunt
Applications for these
motors vary but are
often for larger
applications such as
unwind brake
generators,
conveyors, mixers etc.
1. D.C. Compound- Short Shunt
Applications for these
motors vary but are
often for larger
applications such as
unwind brake
generators,
conveyors, mixers etc.
Motor direction reversal of rotation
Wrap up
1.Explain types of D.C. Motors
2.Find out the equations of V and I for each type
3. How will you change the of direction of rotation of Motor
1.Explain types of D.C. Motors
2.Find out the equations of V and I for each type
3. How will you change the of direction of rotation of Motor
Motor direction reversal of rotation
What actually Back emf in Motor does?(Significance)
ln order to understand lhe significance of back EMF, let us see what would happen if there were no
back EMF.
Let's make upan example of a fictitious parallel DC moton,11h fixed magnets, supply voltage Eoft2
V, Armature resistance of 0.1 Ohm.
+
U there is no back EMF, U,e armature will draw a current of 120 A.
Ea I •R (Ohm·s Law)
It draws a power of 1440 watts (Ex I) from the source
Eb)l:;ffi'Ri<
•
_.,, 1a, _ _: ,j·l"
E
P= E*I = • •
Produces a beating of 1440 Watts i.e. it is power loss PR
All the power drawn from thesource is gone into beating. There is no power left to do any mechanical work
(as per oonservation of ene1·gyprinciple).
ln order to understand lhe significance of back EMF, let us see what would happen if there were no
back EMF.
Let's make upan example of a fictitious parallel DC moton,11h fixed magnets, supply voltage Eoft2
V, Armature resistance of 0.1 Ohm.
+
U there is no back EMF, U,e armature will draw a current of 120 A.
Ea I •R (Ohm·s Law)
It draws a power of 1440 watts (Ex I) from the source
Eb)l:;ffi'Ri<
•
_.,, 1a, _ _: ,j·l"
E
P= E*I = • •
Produces a beating of 1440 Watts i.e. it is power loss PR
All the power drawn from thesource is gone into beating. There is no power left to do any mechanical work
(as per oonservation of ene1·gyprinciple).
What actually Back emf in Motor does?(Significance)
Howeve1·, au the voltage is not dropped by LR in the armature.
As the armature sta,ts moving, the movement of the armature in the field induces a voltage in the
annature winding that ends upopposing and cancelling out part of thesupply voltage.This opposing
voltage is what we call the back EMF.
Now the supply voltage of 12Vapplied across the armature gets
split internally as asum ofhvo drops- l, the J.R dropand 2. the
back EMFdrop.
E=Eb+( l a*R a )
•, +,vfi.w- •
I·
◊t
IIMh
&,
:-.
lo rSl>OO
- '
E is supply voltage E1,is back EMF R. is resistant-e of armature winding la is the a1111atm·e current
In practice, the resistant-e of the armature is small enough that the J.R d r o p (at normal operating
currents) is really small compared to the supply voltage.
For the sake of simplicity, lei's try to neglect the 1-R drop and see what happens
1
E= E1,
Howeve1·, au the voltage is not dropped by LR in the armature.
As the armature sta,ts moving, the movement of the armature in the field induces a voltage in the
annature winding that ends upopposing and cancelling out part of thesupply voltage.This opposing
voltage is what we call the back EMF.
Now the supply voltage of 12Vapplied across the armature gets
split internally as asum ofhvo drops- l, the J.R dropand 2. the
back EMFdrop.
E=Eb+( l a*R a )
•, +,vfi.w- •
I·
◊t
IIMh
&,
:-.
lo rSl>OO
- '
E is supply voltage E1,is back EMF R. is resistant-e of armature winding la is the a1111atm·e current
In practice, the resistant-e of the armature is small enough that the J.R d r o p (at normal operating
currents) is really small compared to the supply voltage.
For the sake of simplicity, lei's try to neglect the 1-R drop and see what happens
1
E= E1,
What actually Back emf in Motor does?
When motor starts Armature isnot-moving
Thatis,in practical terms, theback EMFalmost balances ontthesupplyvoltage (leaving
only a small fraction of the supply voltage to be taken up as I.R drop in the armature).
The armature current is very high, only limited by the small res'istance of the armature.
The initial torque is also very high
As the annature accelerates due to the torque, and gains rotational speed, the back EMF grows.
E= Eb+ (la * R a ) Eb = E - (la • Ra )
As the back EMF grows, the current drops, and the torque alsoreduces. Itall settles at the point
where the torque is equal to the load.
For a r s o n a ble load and a small armature resistance, the back EMF would be n rly equal to
the supply voltage.
When motor starts Armature isnot-moving
Thatis,in practical terms, theback EMFalmost balances ontthesupplyvoltage (leaving
only a small fraction of the supply voltage to be taken up as I.R drop in the armature).
The armature current is very high, only limited by the small res'istance of the armature.
The initial torque is also very high
As the annature accelerates due to the torque, and gains rotational speed, the back EMF grows.
E= Eb+ (la * R a ) Eb = E - (la • Ra )
As the back EMF grows, the current drops, and the torque alsoreduces. Itall settles at the point
where the torque is equal to the load.
For a r s o n a ble load and a small armature resistance, the back EMF would be n rly equal to
the supply voltage.
Torque Equation of DCMotor
Torque actingon a bodyis quantitativelydefined as the product of force acting on the body and
perpendicular distance of the line of action of force from the axisof rotation.
'l11e equation of torque is given by,
..
R
a sin( ) ----(1)
Qualitatively , torque is the tendency of a force to cause a
rotational motion, or to bring about a change in rotational
motion.
Visualize the below shown de motor front-view. Youwill find that each
conductor experiences a force and the conductors lie near thesurface of
the rotor at a common radius from its center. Hence torque is produced
at the circumference of the rotor and rotor sta1tsrotating.
Torque actingon a bodyis quantitativelydefined as the product of force acting on the body and
perpendicular distance of the line of action of force from the axisof rotation.
'l11e equation of torque is given by,
..
R
a sin( ) ----(1)
Qualitatively , torque is the tendency of a force to cause a
rotational motion, or to bring about a change in rotational
motion.
Visualize the below shown de motor front-view. Youwill find that each
conductor experiences a force and the conductors lie near thesurface of
the rotor at a common radius from its center. Hence torque is produced
at the circumference of the rotor and rotor sta1tsrotating.
Torque Equation of DCMotor
When a DC machine is loaded either as a motor or as a generator, the rotor conductors carry current. These
conductors lie in the magnetic field of the air gap.
Thus, each conductor experiences a force.111e conductors lie near the surface of the rotor at a common radius
from its centre. Hence, a torque is produced around the cil'cumference of the rotor, and the ,·otor starts
rotating.
When the machine operates as a generator at a constant speed, this torque is equal and opposite to that
provided by U1e prime mover.
When the machine is operating as a motor, the torque is transfen-ed to the shaft of the rotor and drives the
mechanical load. The exprnssion is the same for the generator and motor.
When the current-canying current is placed in the magnetic field, a force is exerted on it whichexerts turning
moment or torque F x r. This torque is p,'Oduced due to U1e electromagnetic effect, hence is
called Electromagnetic torque.
The torque which is produced in the annature is not fully used at the shaft for doing the useful work. Some
pa,t of it gets lost due to mechanical losses. '111e torque which is used for doing useful work in known as
the shafttorque.
When a DC machine is loaded either as a motor or as a generator, the rotor conductors carry current. These
conductors lie in the magnetic field of the air gap.
Thus, each conductor experiences a force.111e conductors lie near the surface of the rotor at a common radius
from its centre. Hence, a torque is produced around the cil'cumference of the rotor, and the ,·otor starts
rotating.
When the machine operates as a generator at a constant speed, this torque is equal and opposite to that
provided by U1e prime mover.
When the machine is operating as a motor, the torque is transfen-ed to the shaft of the rotor and drives the
mechanical load. The exprnssion is the same for the generator and motor.
When the current-canying current is placed in the magnetic field, a force is exerted on it whichexerts turning
moment or torque F x r. This torque is p,'Oduced due to U1e electromagnetic effect, hence is
called Electromagnetic torque.
The torque which is produced in the annature is not fully used at the shaft for doing the useful work. Some
pa,t of it gets lost due to mechanical losses. '111e torque which is used for doing useful work in known as
the shafttorque.
Torque Equation of DCMotor
ToestabLish the torque equation, let us first consider the basiccircuit diagram of a DC motor,and its voltage
equation.
Eis the supply voltage Eb is the back emf produced
+
E
1
111 R.,are the armature current and annature resistance
respectively
-
+ --( 2 )
lo Shaft
But keeping in mind that our purpose is to derive the torque
equation of DC motor wemultiply bothsides ofequation (2)
by•1.
---( 3 )
VYhere, is the electrical power input to the armature.
2
• is the copper loss in the armature.
ToestabLish the torque equation, let us first consider the basiccircuit diagram of a DC motor,and its voltage
equation.
Eis the supply voltage Eb is the back emf produced
+
E
1
111 R.,are the armature current and annature resistance
respectively
-
+ --( 2 )
lo Shaft
But keeping in mind that our purpose is to derive the torque
equation of DC motor wemultiply bothsides ofequation (2)
by•1.
---( 3 )
VYhere, is the electrical power input to the armature.
2
• is the copper loss in the armature.
Torque Equation of DCMotor
We know that,
Totalelectrical powersupplied to tbe armature = Mechanical power developed by Ute armature +
losses due to armature resistance
·11,e mechanical power developed bythearmature is Pm, D = C : : :
Also, the mechanical power U1at rotates the armature can be given regarding torque T andspeed n.
D = DD =2DDr --( 5 )
Wheren isin revolution perseronds (rps) andTis in Newton-Meter.
Equate (4) and (5), we get
□---
2
But Et, is giveA-lly =
[l
(,()
We know that,
Totalelectrical powersupplied to tbe armature = Mechanical power developed by Ute armature +
losses due to armature resistance
·11,e mechanical power developed bythearmature is Pm, D = C : : :
Also, the mechanical power U1at rotates the armature can be given regarding torque T andspeed n.
D = DD =2DDr --( 5 )
Wheren isin revolution perseronds (rps) andTis in Newton-Meter.
Equate (4) and (5), we get
□---
2
But Et, is giveA-lly =
[l
(,()
Toraue Rquation ofDCMotor
---.
P
.
c!>
-,
J
J t@(il3ih) alid
N
h
e Wh(ll'e n is the speed in (rps).
r
e
e
V
0
I
u
l
i
0
n
s
t
h
e
p
e
r
s
p
e
e
d
m
n
u
---.
P
.
c!>
-,
J
J t@(il3ih) alid
N
h
e Wh(ll'e n is the speed in (rps).
r
e
e
V
0
I
u
l
i
0
n
s
t
h
e
p
e
r
s
p
e
e
d
m
n
u
Torque Equation of DCMotor
Where N is the speed in revolution per minute (rpm) and
.::J
=-
60
Where n is the speed in (rps).
<l>nZP
Hem.-.e we can w1ite torque equationas,
.J =,
2
<llnZP
Cl>ZP
=--
2
0.159 • <l>ZP
For a particular DC Motor, the mmiber of poles (P) and the number of conductors per parallel path (Z/A)
are c-onstant:.
2
Where N is the speed in revolution per minute (rpm) and
.::J
=-
60
Where n is the speed in (rps).
<l>nZP
Hem.-.e we can w1ite torque equationas,
.J =,
2
<llnZP
Cl>ZP
=--
2
0.159 • <l>ZP
For a particular DC Motor, the mmiber of poles (P) and the number of conductors per parallel path (Z/A)
are c-onstant:.
2
Torque Equation of DCMotor
ere,
ere,
Torque Equation of DCMotor
Thus, from the aboveequation, it is clear thatthe torque produced in the31111ature isdirectly proportional
to the flux per pole and the am1ature current.
111e direction of electromagnetic torque developed in thearmaturedepends upon thecurrent in armature
conductors. lf eitl1er of the two (Oux or current) is reversed the direction of torque produced is reversed
and hence thedirection of rotation. But when both are reversed, and direction of torquedoes not change.
Thus, from the aboveequation, it is clear thatthe torque produced in the31111ature isdirectly proportional
to the flux per pole and the am1ature current.
111e direction of electromagnetic torque developed in thearmaturedepends upon thecurrent in armature
conductors. lf eitl1er of the two (Oux or current) is reversed the direction of torque produced is reversed
and hence thedirection of rotation. But when both are reversed, and direction of torquedoes not change.
Types of DCMotor
As the name signifies, the field coils or field
windings aJ'e energised bya separate DCsource
as shown in the circuit diagram shown below:
+
+
Field
DC
Supply
I
As tl1e name implies self-excited, hence, in this
type of motor, the current in the windings is
supplied bythe machine or motor itself.
Shuntwoundorshunt motor
Series wound orseries motor
Com_pound woundoroomp0und motor.
As the name signifies, the field coils or field
windings aJ'e energised bya separate DCsource
as shown in the circuit diagram shown below:
+
+
Field
DC
Supply
I
As tl1e name implies self-excited, hence, in this
type of motor, the current in the windings is
supplied bythe machine or motor itself.
Shuntwoundorshunt motor
Series wound orseries motor
Com_pound woundoroomp0und motor.
Types of DCMotor
DCMotor Shunt wound or shunt motor
This is the most common types of DC Motor. Hercthe field winding
is connected in parallel with the armature as shown in the figure
below:
+·}-+--,
+ 0------.----,
1,
Armature
Shunt
Field
Q011ogn11mm.atlc
DCMotor Shunt wound or shunt motor
This is the most common types of DC Motor. Hercthe field winding
is connected in parallel with the armature as shown in the figure
below:
+·}-+--,
+ 0------.----,
1,
Armature
Shunt
Field
Q011ogn11mm.atlc
Types of DCMotor
SeJ&erdted DCMotor
+ o------ - -,--
t,
Arma1ure
Shunt wound or shunt motor
111e current, voltage and power e<)llations for a shunt motor are
written as follows.
Byapplying KCL at junction in the above figure.
Shunl
Field
......(I)
Where,
I or .J is the input line current
C is the armatUJ'ecuri·ent
or h is the shunt field current
The voltage equations are written by using Kirchhoff's voltage law{KVL) for the field winding cirCllit.
......(2)
For armature winding circuit the equation will be given as:
+ ......(3)
SeJ&erdted DCMotor
+ o------ - -,--
t,
Arma1ure
Shunt wound or shunt motor
111e current, voltage and power e<)llations for a shunt motor are
written as follows.
Byapplying KCL at junction in the above figure.
Shunl
Field
......(I)
Where,
I or .J is the input line current
C is the armatUJ'ecuri·ent
or h is the shunt field current
The voltage equations are written by using Kirchhoff's voltage law{KVL) for the field winding cirCllit.
......(2)
For armature winding circuit the equation will be given as:
+ ......(3)
Types of DCMotor
SeJ&erdted DCMotor
lT-=lA + I F
Shunt wound or shunt motor
111e power equation is givenas:
+ <>---------, -
I, Power input = mechanical power developed + losses in the
annature + loss in thefield.
Shunt
Field Armaiure
+
2
from(2), a
• •
h
=r +
2
+ .
D □-
2r
Put this in (4),
- .
- -
(
-
_r
a)-
2
From (1),
s + + -
(
2
h
- - • )
SeJ&erdted DCMotor
lT-=lA + I F
Shunt wound or shunt motor
111e power equation is givenas:
+ <>---------, -
I, Power input = mechanical power developed + losses in the
annature + loss in thefield.
Shunt
Field Armaiure
+
2
from(2), a
• •
h
=r +
2
+ .
D □-
2r
Put this in (4),
- .
- -
(
-
_r
a)-
2
From (1),
s + + -
(
2
h
- - • )
Types of DCMotor
8eJ&Gclted DCMotor Shunt wound or shunt motor
- ( - . )
Armalure
From (3), D =□ + •
Shunt
Field
[J ......(5)
Multiplying equation (3) by we get the following equations.
......(3)
•J
• - • +
2 ......(6)
......(7)
8eJ&Gclted DCMotor Shunt wound or shunt motor
- ( - . )
Armalure
From (3), D =□ + •
Shunt
Field
[J ......(5)
Multiplying equation (3) by we get the following equations.
......(3)
•J
• - • +
2 ......(6)
......(7)
Types of DCMotor
is the electJical power supplied to the am1ature of the motor.
is the electJical power supplied to the am1ature of the motor.
Concept of Load Torque
Tol'que has 2 main components: load torque and acceleration torque.
Load torque is the amount of torque constantly required for application and includes friction load
and gravitational load.
Load tol'que: The to1-que which is generated due to load connected to the motor.
DCmotor is meant to produce rotational kinetic energyand it does byexerting tol'que on the load.
That TORQUE, which it exerts upon the load through its shaft,iscalled tbeload t01-que.
Tol'que has 2 main components: load torque and acceleration torque.
Load torque is the amount of torque constantly required for application and includes friction load
and gravitational load.
Load tol'que: The to1-que which is generated due to load connected to the motor.
DCmotor is meant to produce rotational kinetic energyand it does byexerting tol'que on the load.
That TORQUE, which it exerts upon the load through its shaft,iscalled tbeload t01-que.
Types of Loads
Definition: 111e device which takes elect1ical energy is known as the electric load.
In other words, the electrical load is a device thatconsumes electrical energy in the form of the current and
transforms it into other fom1s like heat, light, work, etc.
Definition: 111e device which takes elect1ical energy is known as the electric load.
In other words, the electrical load is a device thatconsumes electrical energy in the form of the current and
transforms it into other fom1s like heat, light, work, etc.
Types of Loads
Resistive I.oad
The resistive load obstructs the flow of electrical energy in the circuit and converts it into thermalenergy,
due to which the energy dropout occurs in the circuit. Loadsconsisting of any heating element aJ'eclassified
as resistive loads.
·111e lamp and the heater, incandescent lights, toasters, ovens, space
heatersand coffee makers are the examples of the resistive load.
The resistive loads take power in sucl1 a way so that the current and the
voltage wave remain in the same phase. 1110s the power factor of the
resistive load remains in unity.
Resistive Load
Resistive I.oad
The resistive load obstructs the flow of electrical energy in the circuit and converts it into thermalenergy,
due to which the energy dropout occurs in the circuit. Loadsconsisting of any heating element aJ'eclassified
as resistive loads.
·111e lamp and the heater, incandescent lights, toasters, ovens, space
heatersand coffee makers are the examples of the resistive load.
The resistive loads take power in sucl1 a way so that the current and the
voltage wave remain in the same phase. 1110s the power factor of the
resistive load remains in unity.
Resistive Load
Types of Loads
Inductive toad
The inductive loads use the magnetic field for doing the work.
These are found in a variety of household items and de,ices ""th moving pa,ts, including fans, vacuum
cleaners, dishwashers, washing machines and the compressors in refrigerators and air conditioners. The
transformers, generators, motor are the examples of the load.
l.nductiw Load
The inductive load has a coil which stores magnetic energy when the current pass through it. Thecurrent
\\OJVC of the inductive load is lagging behind lhe voltage wave, and the power factorof the inductive load is
alsolagging.
Inductive toad
The inductive loads use the magnetic field for doing the work.
These are found in a variety of household items and de,ices ""th moving pa,ts, including fans, vacuum
cleaners, dishwashers, washing machines and the compressors in refrigerators and air conditioners. The
transformers, generators, motor are the examples of the load.
l.nductiw Load
The inductive load has a coil which stores magnetic energy when the current pass through it. Thecurrent
\\OJVC of the inductive load is lagging behind lhe voltage wave, and the power factorof the inductive load is
alsolagging.
Types of Loads
Capacitive Load
ln the capacitive load, the current wave is leading the voltagewave.
TI1e examples of capacitive loads are capacitor bank, three phase induction motor starting circuit, etc.TI1e
power factor of such type of loads is leading. In engineering, capacitive loads do not exist in a stand-alone
format. No devices are classified as capacitive in the way light bulbs are categorized as resistive, and air
conditioners are labeled inductive.
I
Capacitive Load
ln the capacitive load, the current wave is leading the voltagewave.
TI1e examples of capacitive loads are capacitor bank, three phase induction motor starting circuit, etc.TI1e
power factor of such type of loads is leading. In engineering, capacitive loads do not exist in a stand-alone
format. No devices are classified as capacitive in the way light bulbs are categorized as resistive, and air
conditioners are labeled inductive.
I
Types of Electrical Loads in PowerSystem
Domestic load
The domestic load is defined as the total energy consumed by the electiical appliances in the household
work. It depends on the livingstandard, weather and type of residence.
11iedomestic loads mainly consist oflights, fan, refrigerator, air conditioners, mixer,grinder, heater, ovens,
small pumping, motor, etc.Most of the domestic loads are -onnected for onlysome hours duringa day. For
example, lighting load is connected for few hours during night time.
The domestic load consume very little power and also independent from frequency. ·niis load largely
consists of lighting, cooling or heating.
Domestic load
The domestic load is defined as the total energy consumed by the electiical appliances in the household
work. It depends on the livingstandard, weather and type of residence.
11iedomestic loads mainly consist oflights, fan, refrigerator, air conditioners, mixer,grinder, heater, ovens,
small pumping, motor, etc.Most of the domestic loads are -onnected for onlysome hours duringa day. For
example, lighting load is connected for few hours during night time.
The domestic load consume very little power and also independent from frequency. ·niis load largely
consists of lighting, cooling or heating.
Types of Electrical Loads in PowerSystem
Comme ci oad
Commercial loadmainly consist ofelectrical loads thataremeant to be usedcommercially, such as lightning
ofshops, offices, advertisements, etc., Fans, Heating, Airconditioning and many other electtical appliances
used in establishmentssuch as market restaurants, etc.are considered as a commercial load.
'I1lis type of load occurs for more hours during the day as compared to the domestic load.
Comme ci oad
Commercial loadmainly consist ofelectrical loads thataremeant to be usedcommercially, such as lightning
ofshops, offices, advertisements, etc., Fans, Heating, Airconditioning and many other electtical appliances
used in establishmentssuch as market restaurants, etc.are considered as a commercial load.
'I1lis type of load occurs for more hours during the day as compared to the domestic load.
Types of Electrical Loads in PowerSystem
Industrial Loads
Industrial load consists of small-scale industries, medium scale industries, large scale industries, heavy
industries and cottage industries.
The induction motor forms a high proportion of the composite load. Industrial loads may be connected
during the whole day.
The industrial loads are the t-omposite load.The composite load is a function of frequency and voltage and
its fonu a major part of the system load.
Industrial Loads
Industrial load consists of small-scale industries, medium scale industries, large scale industries, heavy
industries and cottage industries.
The induction motor forms a high proportion of the composite load. Industrial loads may be connected
during the whole day.
The industrial loads are the t-omposite load.The composite load is a function of frequency and voltage and
its fonu a major part of the system load.
Types of Electrical Loads in PowerSystem
gricultureflnigation Load
Motors and pumps usedin irrigation systems tosupply thewaterfor farming come ,uider thiscatego,y.
Generally,irrigation loads a resupplied during off-peak or night hours.
Th.is typeofload is mainly motor pumps-sets load for inigation pw-poses. '111e load factorof this load is very
small e.g. 0 . 1 5-0 . 2 0 .
gricultureflnigation Load
Motors and pumps usedin irrigation systems tosupply thewaterfor farming come ,uider thiscatego,y.
Generally,irrigation loads a resupplied during off-peak or night hours.
Th.is typeofload is mainly motor pumps-sets load for inigation pw-poses. '111e load factorof this load is very
small e.g. 0 . 1 5-0 . 2 0 .
Types of Electrical Loads in PowerSystem
Some Other Classifications Of Electrical Loads
According To Load Nahire
Linear loads: Linear loads like transformers, motors follow ohm's law (as long as their core isnot
saturated) i.e. their current changelinea,·ly with the change in applied voltage.
Non-linear loads: non linear load likeswitching regulator current is not linearly changing with the
change in the applied voltage, it takes lesser current as applied voltage increases.
According To Phases
Singlephaseloads
•Three phaseloads
Some Other Classifications Of Electrical Loads
According To Load Nahire
Linear loads: Linear loads like transformers, motors follow ohm's law (as long as their core isnot
saturated) i.e. their current changelinea,·ly with the change in applied voltage.
Non-linear loads: non linear load likeswitching regulator current is not linearly changing with the
change in the applied voltage, it takes lesser current as applied voltage increases.
According To Phases
Singlephaseloads
•Three phaseloads
Dynamics of Motor and Load Combination
When an electric motor rotates, it is usually connected to a load which bas a rotational or translational
motion.111e speed of the motor may be different from thatof the load.
In the translational motion, the position of the body changes from point to point in space. The speed of the
load may be different from that of the motor.
If the load bas different parts, their speed may be different. Some part of the rotor may rotatewhile others
may go through a translational motion.
Motor
T
J = Polar moment of inertia of motor load referred to
the motor shaft,kg-m•
Olm- instantaneous angular velocity of the motor
shaft, rad/sec.
tqul ltnt Motor I.oldSvst•m
T - the instantaneous value of developed motor
torque, N-m.
T,- the instantaneous value of load torque, referred
to a motor shaft,N-m.
When an electric motor rotates, it is usually connected to a load which bas a rotational or translational
motion.111e speed of the motor may be different from thatof the load.
In the translational motion, the position of the body changes from point to point in space. The speed of the
load may be different from that of the motor.
If the load bas different parts, their speed may be different. Some part of the rotor may rotatewhile others
may go through a translational motion.
Motor
T
J = Polar moment of inertia of motor load referred to
the motor shaft,kg-m•
Olm- instantaneous angular velocity of the motor
shaft, rad/sec.
tqul ltnt Motor I.oldSvst•m
T - the instantaneous value of developed motor
torque, N-m.
T,- the instantaneous value of load torque, referred
to a motor shaft,N-m.
Dynamics of Motor and Load Combination
Motor
T
}
r, ) 1---
Torque Equation of Motor Load System of Fig. can be
desc1ibed by the following fundamental torque
equation:
Equtval.-nt Motor load System
ill +
.............(1)
Equation (1) is applicable to variable inertia drives such as mine winders, reel drives, industrial robots.
For drives with constant inertia (a property of matter by which it continues in its existing state of rest or
unifonn motion ina straight line, unless that state ischanged by an external force.), (dJ/dt) = o.
r:_d_ 1 • ti L_ .............(2)
In the above equation the motor torque is considered as an applied torque and the load torque asa resisting
torque.
Equation (2) shows that torque de,•eloped by motor is counter balanced by nload torqueT, and a dynamic
Motor
T
}
r, ) 1---
Torque Equation of Motor Load System of Fig. can be
desc1ibed by the following fundamental torque
equation:
Equtval.-nt Motor load System
ill +
.............(1)
Equation (1) is applicable to variable inertia drives such as mine winders, reel drives, industrial robots.
For drives with constant inertia (a property of matter by which it continues in its existing state of rest or
unifonn motion ina straight line, unless that state ischanged by an external force.), (dJ/dt) = o.
r:_d_ 1 • ti L_ .............(2)
In the above equation the motor torque is considered as an applied torque and the load torque asa resisting
torque.
Equation (2) shows that torque de,•eloped by motor is counter balanced by nload torqueT, and a dynamic
Dynamics of Motor and Load Combination
torque J(dw,.,fdt). Torque component J(dw,.,fdt) is called the dynamic 10,·que because it is present only
during the transient operations. i.e., when the speed of the drive varies.
torque J(dw,.,fdt). Torque component J(dw,.,fdt) is called the dynamic 10,·que because it is present only
during the transient operations. i.e., when the speed of the drive varies.
Dynamics of Motor and Load Combination
Motor
T
l
r, )
The acceleration or deceleration of the drive mainly
depends on whether tbe load torque isgreater or less than
1--- the motor torque.
.J [.J
Equtval.nt MotorI.old System
Case1)When >
-- >
Case2)When <
-- <
i.e.thedrivewill bedecelerating and, particulal'ly coming torest.
Motor
T
l
r, )
The acceleration or deceleration of the drive mainly
depends on whether tbe load torque isgreater or less than
1--- the motor torque.
.J [.J
Equtval.nt MotorI.old System
Case1)When >
-- >
Case2)When <
-- <
i.e.thedrivewill bedecelerating and, particulal'ly coming torest.
Characteristics of DC Shunt Motor
Generally, three characteristic curves are considered impo1ia11t for DC motors related to its performance
which are, (i) Torque vs. armature cuITent, (ii) Speed vs. armature current and (iii) Speed vs. torque.
+ u---------
l,
Armature
Here, supply voltage is constant. Same voltage is given to field winding
and armature.
Shunt
Field
Where,
h = Filed current
h = Field resistance which is
<.'Onstant
111evoltageequations are written byusing IGrchhofl's voltage law
(KVL) for the field windingcircuit.
C
A
h
::J ,,=- ................(1)
V = supply voltage which is constant.
Generally, three characteristic curves are considered impo1ia11t for DC motors related to its performance
which are, (i) Torque vs. armature cuITent, (ii) Speed vs. armature current and (iii) Speed vs. torque.
+ u---------
l,
Armature
Here, supply voltage is constant. Same voltage is given to field winding
and armature.
Shunt
Field
Where,
h = Filed current
h = Field resistance which is
<.'Onstant
111evoltageequations are written byusing IGrchhofl's voltage law
(KVL) for the field windingcircuit.
C
A
h
::J ,,=- ................(1)
V = supply voltage which is constant.
Characteristics of DC Shunt Motor
As V and 1, are constant, the held
current h isalsoconstant.
As the field cun·ent C h isalso
constant, flux c:JJ is constant in DC
sh wit motor.
As V and 1, are constant, the held
current h isalsoconstant.
As the field cun·ent C h isalso
constant, flux c:JJ is constant in DC
sh wit motor.
Characteristics of DC Shunt Motor
Armature
Shunt
Field
For am1ature winding circuit the equation will be given as:
But Back emf is:
... . -< I >
7 = -□•
J
P<I>
......(2)
Where Kis constantand it is
r
p
D = •
As nux(I) is cm1stant in DCshunt motor,hence I
Where
......(3)
is constant and it is (I)
Armature
Shunt
Field
For am1ature winding circuit the equation will be given as:
But Back emf is:
... . -< I >
7 = -□•
J
P<I>
......(2)
Where Kis constantand it is
r
p
D = •
As nux(I) is cm1stant in DCshunt motor,hence I
Where
......(3)
is constant and it is (I)
Characteristics of DC Shunt Motor
- .J- ......(2)
11,eannature torque is directly proportional to the product of the nu, and the annalure current i.e.Ta« <!>.Ia
Ta« <l>.la .. Ta = <II.la
\-\ 1ere I<,is constant
As 01t, • is constant in DC shunt motor, hence
= .la
Where is constant and it is • <I>
Ta ......(4)
- .J- ......(2)
11,eannature torque is directly proportional to the product of the nu, and the annalure current i.e.Ta« <!>.Ia
Ta« <l>.la .. Ta = <II.la
\-\ 1ere I<,is constant
As 01t, • is constant in DC shunt motor, hence
= .la
Where is constant and it is • <I>
Ta ......(4)
Characteristics of DC Shunt Motor
Refer following equations
= ······<2) Ta= .la
......(4)
D ......(3)
Put (3) in (2)
Q
•
Y= D
][J=-
• L
=---+-
......(5)
Comparing equation (5) it with standard equation of a straight line, Y= nL,+C
vi rnnt
0
current,.I<i.-+ . _:i----------
Refer following equations
= ······<2) Ta= .la
......(4)
D ......(3)
Put (3) in (2)
Q
•
Y= D
][J=-
• L
=---+-
......(5)
Comparing equation (5) it with standard equation of a straight line, Y= nL,+C
vi rnnt
0
current,.I<i.-+ . _:i----------
Characteristics of DC Shunt Motor
---
V I , + -- - r n n
0 cumnt,.I a.--. _
t
- ..._._ ....
We find that the characteristic is a straight line with intercept
on speed axis equal to V/K,,called no-load speed i.e when 1. is
negligibly small just to provide torque toovercome friction and
windage.
TI1e characteristic show that de shunt motor speed remains
almost t-onstant from no-lo.1d ( 1.,. o) to full load ( 1.=rated
value) and that is why deshunt motor is used in applications
wherespeedisrequiredtoremain almostconstant-throughout
the operation e,g Lathes, snioning and weaving machines,
dolls etc.
If annature reaction is taken into ae<.-ount, speed drops
slowly, represented by tl1e red curve.
---
V I , + -- - r n n
0 cumnt,.I a.--. _
t
- ..._._ ....
We find that the characteristic is a straight line with intercept
on speed axis equal to V/K,,called no-load speed i.e when 1. is
negligibly small just to provide torque toovercome friction and
windage.
TI1e characteristic show that de shunt motor speed remains
almost t-onstant from no-lo.1d ( 1.,. o) to full load ( 1.=rated
value) and that is why deshunt motor is used in applications
wherespeedisrequiredtoremain almostconstant-throughout
the operation e,g Lathes, snioning and weaving machines,
dolls etc.
If annature reaction is taken into ae<.-ount, speed drops
slowly, represented by tl1e red curve.
Characteristics of DC Shunt Motor
From (4) Ta= ,la
c.u Io..--+
Therefore, in a de shunt motor, the torque increases linearly
with am,ature cun·ent as shown by the black cuive.
But, for larger 1., the net flux per pole decreases due to the
demagnetizing effect ofam1atlU-e reaction and hencethecuive
deviates from stn.,ight line asshown by red cuive.
From (4) Ta= ,la
c.u Io..--+
Therefore, in a de shunt motor, the torque increases linearly
with am,ature cun·ent as shown by the black cuive.
But, for larger 1., the net flux per pole decreases due to the
demagnetizing effect ofam1atlU-e reaction and hencethecuive
deviates from stn.,ight line asshown by red cuive.
Characteristics of DC Shunt Motor
Flux <Disconstant in DCshllnt motor. Refer following equations
D = Ll- ......(2) Ta= .la
......(3)
......(4)
□
•C
[j
......(5)
[J =- --+-
From (4) Ta= .Ia
JE_
3
Put this in equation Cs)
Q...
J
......(6)
□=- +-
Flux <Disconstant in DCshllnt motor. Refer following equations
D = Ll- ......(2) Ta= .la
......(3)
......(4)
□
•C
[j
......(5)
[J =- --+-
From (4) Ta= .Ia
JE_
3
Put this in equation Cs)
Q...
J
......(6)
□=- +-
Chara
"
cteristics of DC Shunt Motor
From this, it is observed thatspeed N is proportional
to torque.
"
cteristics of DC Shunt Motor
From this, it is observed thatspeed N is proportional
to torque.
Characteristics of DC Shunt Motor
[ . ]
e---+-
......(6)
r :;::-:::..._--
z
i
From this equation speed-torque characteristics of de shunt
motor can be drawn whicb turns out to be a straight line
shown by black cu!'ve.
0
When armature 1·eaction is also considered i.e fl1Lx is no
longer constant , the speed-torque equation becomes
□=-
□ • C
= <I)
<!>
Obviously, clue to armature reaction, as OIL< decreases the
+-
r<1> <I> ]
Cl)
Torque.,Ta. ..►.
[ . ]
e---+-
......(6)
r :;::-:::..._--
z
i
From this equation speed-torque characteristics of de shunt
motor can be drawn whicb turns out to be a straight line
shown by black cu!'ve.
0
When armature 1·eaction is also considered i.e fl1Lx is no
longer constant , the speed-torque equation becomes
□=-
□ • C
= <I)
<!>
Obviously, clue to armature reaction, as OIL< decreases the
+-
r<1> <I> ]
Cl)
Torque.,Ta. ..►.
Characteristics of DC Shunt Motor
firstterm increases more than the s nd term , therefore the
speed drops more rapidly with increase in torque.
firstterm increases more than the s nd term , therefore the
speed drops more rapidly with increase in torque.
Speed control methods of DC shunt motor
Back emf Ebof a DC motor is nothing but the induced emf in am1atul'e conductol's due to rotation of the
armature in magnetic field. Thus, the magnitude of Ebe.in be given by EMF equation of a DC generator.
p ( J )
......(1)
(where, P =no.of poles, 0= Oux/pole, N=speed in rpm, Z= no.ofarmatuJ'econductors, A= parallel paths)
Ei,can also begiven as, ......(2)
thus, from the above equations (1)
• •
......(3)
=
but,fora DCmotor A, PandZareconstants 0:- ......(4)
111isshowsthe speed ofa de motor isdirectly proportional to the backemfand inversely proportional tothe
fllLX per pole.
Back emf Ebof a DC motor is nothing but the induced emf in am1atul'e conductol's due to rotation of the
armature in magnetic field. Thus, the magnitude of Ebe.in be given by EMF equation of a DC generator.
p ( J )
......(1)
(where, P =no.of poles, 0= Oux/pole, N=speed in rpm, Z= no.ofarmatuJ'econductors, A= parallel paths)
Ei,can also begiven as, ......(2)
thus, from the above equations (1)
• •
......(3)
=
but,fora DCmotor A, PandZareconstants 0:- ......(4)
111isshowsthe speed ofa de motor isdirectly proportional to the backemfand inversely proportional tothe
fllLX per pole.
Speed control methods of DC shunt motor
(
LI
"
.....,(4)
......(2) ...
[l
·111e aboveequation shows that the speed depends upon the supply voltage v,the annature circuit resistance
R.,and thefield flux <1>,which is produced by the field current.
In practice, the variation of these three factors is used for speed contJ'OI. n,us, there are three geneml
methods of speed control ofO.C. Motors.
Resistanu variation in the armature circuit: This method is called armature resistanu control or
Rheostat control.
Variation of field flux - This method is called field flux control.
Variation of the a lied voltage. This method is also called armature uoltage control.
(
LI
"
.....,(4)
......(2) ...
[l
·111e aboveequation shows that the speed depends upon the supply voltage v,the annature circuit resistance
R.,and thefield flux <1>,which is produced by the field current.
In practice, the variation of these three factors is used for speed contJ'OI. n,us, there are three geneml
methods of speed control ofO.C. Motors.
Resistanu variation in the armature circuit: This method is called armature resistanu control or
Rheostat control.
Variation of field flux - This method is called field flux control.
Variation of the a lied voltage. This method is also called armature uoltage control.
Speed control methods of DC shunt motor
Theclassification ofspeed controlmethods for a D C s h u n tmo to r a.reas follows. These twomethodsare:
1. A,mature Control Methods
2. Field Control Methods
Armature Controlled DCShunt Motor ...
Field Controlled DCShunt Motor
a)A1111ature Resistance Control
b)A1111ature VoltageControl
Variation in field nux·111is method is known as Field
Flux Control.
Theclassification ofspeed controlmethods for a D C s h u n tmo to r a.reas follows. These twomethodsare:
1. A,mature Control Methods
2. Field Control Methods
Armature Controlled DCShunt Motor ...
Field Controlled DCShunt Motor
a)A1111ature Resistance Control
b)A1111ature VoltageControl
Variation in field nux·111is method is known as Field
Flux Control.
Speed control methods of DC shunt motor
Resistance variation in the armature circuit: 'This method is called armature resistance control or
Rheostat oontrol.
+
R,,
V
In this method, a variable series resistor R. is putin thearmature
circuit. The figlll'e (a) above shows the process of connection for
a shunt motor. In this case, the field is directly connected across
tbe supply and therefore tbe fllL, <I>is not affected byvariation of
R,,.
Rsh
The voltage drop in R, reduces the voltage applied to the
a1111ature, and therefore the speed is reduced.
Speed control of a d.c.Slum! motor by
annature resistance conh•ol.
Resistance variation in the armature circuit: 'This method is called armature resistance control or
Rheostat oontrol.
+
R,,
V
In this method, a variable series resistor R. is putin thearmature
circuit. The figlll'e (a) above shows the process of connection for
a shunt motor. In this case, the field is directly connected across
tbe supply and therefore tbe fllL, <I>is not affected byvariation of
R,,.
Rsh
The voltage drop in R, reduces the voltage applied to the
a1111ature, and therefore the speed is reduced.
Speed control of a d.c.Slum! motor by
annature resistance conh•ol.
Speed control methods of DC shunt motor
Resistance variation in the armature circuit: This method is called armature resistance control or
Rheostat control.
Armature
For am1atul'e winding cil'cuit the equation " U be given as:
Shunt [ e
Field
+ ] • ...
□ =
□
- r • ......(2)
DCShunt Motor
♦
V ....
For arn1ahue winding circuit with presence of Re,
given as:
□= +r ·c + , ...
the equation will be
•< +n l [I =
Resistance variation in the armature circuit: This method is called armature resistance control or
Rheostat control.
Armature
For am1atul'e winding cil'cuit the equation " U be given as:
Shunt [ e
Field
+ ] • ...
□ =
□
- r • ......(2)
DCShunt Motor
♦
V ....
For arn1ahue winding circuit with presence of Re,
given as:
□= +r ·c + , ...
the equation will be
•< +n l [I =
Speed control methods of DC shunt motor
. . A.iiflb hbfodhi 61]%[email protected]' RJ ii.\Qi§led)ndb!i!xO!lhdi @§i§fah& [email protected]. F 4: · J
Resistance uananon7n tne armarure ctrcuit: 1nis metnoa ,s ca11ea armature resistance conl1'01 or
Rheostat control.
. . A.iiflb hbfodhi 61]%[email protected]' RJ ii.\Qi§led)ndb!i!xO!lhdi @§i§fah& [email protected]. F 4: · J
Resistance uananon7n tne armarure ctrcuit: 1nis metnoa ,s ca11ea armature resistance conl1'01 or
Rheostat control.
Speed control methods of DC shunt motor
Resistance uariation in the armature circuit: This method is called armature resistance conll'ol or
Rheostat conll'OI.
Armature
DCShw1t 111otor
"'
Shunt
Field
+
R, ..
Mere value of Ou., also changes due to change in armature current. But
thatchange will be lesscompare to change in Eb value.
« « •
As Eb value reduces due to addition of Re, speed decreases.
Resistance uariation in the armature circuit: This method is called armature resistance conll'ol or
Rheostat conll'OI.
Armature
DCShw1t 111otor
"'
Shunt
Field
+
R, ..
Mere value of Ou., also changes due to change in armature current. But
thatchange will be lesscompare to change in Eb value.
« « •
As Eb value reduces due to addition of Re, speed decreases.
Speed control methods of DC shunt motor
Resistance uariation in the armature circuit: This method is called armature resistance control or
Rheostat control.
Drawbacks:
A large amount of power is wasted in the external resistance Re.
Armature resistance control is restricted to keep the speed below the nom1al speed of the motor and
increase in the speed above normal level is not possible by this method.
For a given value of R.,, the speed reduction is not constant but varies with the motor load.
Resistance uariation in the armature circuit: This method is called armature resistance control or
Rheostat control.
Drawbacks:
A large amount of power is wasted in the external resistance Re.
Armature resistance control is restricted to keep the speed below the nom1al speed of the motor and
increase in the speed above normal level is not possible by this method.
For a given value of R.,, the speed reduction is not constant but varies with the motor load.
Speed control methods of DCshunt motor
Variation offieldfha tP is method isc«Uedfieldjlwccon o/.
+
V
Since the field current produces the Oux, and if we control the
field current then thespeed can be controlled.
._ -SRe In the shunt motor, speed can be t'OntroUed by connecting a
variable resistor R,,in series \\ilh theshunt field winding.
Rsh In the diagram below resistor, R,, is called the shunt field
re1,•1Jlator.
Speed control ofaD.C.shunt
motor by variation of field jlw:.
To control the flux, the rheostat (variable resistor I ) is added
in series with the field winding \\ill increase the speed (N),
because of this Ou., will decrease. So, the field current is
1-elatively small and hence 1
1R loss is decreased.
Variation offieldfha tP is method isc«Uedfieldjlwccon o/.
+
V
Since the field current produces the Oux, and if we control the
field current then thespeed can be controlled.
._ -SRe In the shunt motor, speed can be t'OntroUed by connecting a
variable resistor R,,in series \\ilh theshunt field winding.
Rsh In the diagram below resistor, R,, is called the shunt field
re1,•1Jlator.
Speed control ofaD.C.shunt
motor by variation of field jlw:.
To control the flux, the rheostat (variable resistor I ) is added
in series with the field winding \\ill increase the speed (N),
because of this Ou., will decrease. So, the field current is
1-elatively small and hence 1
1R loss is decreased.
Speed control methods of DC shunt motor
V a r i a t io1 t o f f i e l d is method iscaUedfieldjluxcontrol.
li; lA+ IF
+
1,
r.
Shunl
Field Armature
·me voltage equations are written byusing Kirchhoff s voltage law(KVL)
for the field winding circuit.
...
u
I=- ................(!)
DC Shunt Motor
+
V
The voltage equations a1-e written by using KirchhoO's voltage law (KVL)
for the field winding circuit wben a variable resistor R.in series with the
shunt field winding.
h \ + ) ................(2)
"
When R,,is added in series with field winding, current in equation (2) is less
compared with equation (1) for constant value ofV. Hence flux decreases and
V a r i a t io1 t o f f i e l d is method iscaUedfieldjluxcontrol.
li; lA+ IF
+
1,
r.
Shunl
Field Armature
·me voltage equations are written byusing Kirchhoff s voltage law(KVL)
for the field winding circuit.
...
u
I=- ................(!)
DC Shunt Motor
+
V
The voltage equations a1-e written by using KirchhoO's voltage law (KVL)
for the field winding circuit wben a variable resistor R.in series with the
shunt field winding.
h \ + ) ................(2)
"
When R,,is added in series with field winding, current in equation (2) is less
compared with equation (1) for constant value ofV. Hence flux decreases and
Speed control methods of DC shunt motor
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Speed control methods of DC shunt motor
0
111is method is easyand convenient.
1\s the shunt field is very small, the power loss in the shunt field is alsosmall.
The flux cannot usually be increased beyond its nonnal values because of the sat11ration of the iron.
111crefore, speed control by nuxis limited to the weakening of the field, which gives an increase inspeed (as N
is inversely proportional to 0tL< <D).
This method is applicable over only to a limited range because if the field is weakened too much, there is a
loss ofstability.
0
111is method is easyand convenient.
1\s the shunt field is very small, the power loss in the shunt field is alsosmall.
The flux cannot usually be increased beyond its nonnal values because of the sat11ration of the iron.
111crefore, speed control by nuxis limited to the weakening of the field, which gives an increase inspeed (as N
is inversely proportional to 0tL< <D).
This method is applicable over only to a limited range because if the field is weakened too much, there is a
loss ofstability.
Speed control methods of DC shunt motor
Variation qfthe ap lied ooltage. This method is also called armature ooltage cont1'ol.
In a,mature voltage control method thespeed control is achieved by va,ying the applied voltage in the
.,,.,..,
SupJ)fv
armature winding of the motor.
TI1is speed control method is also known
as Ward Leonard Method. This method
was introduced in 1891.
0CMOI«
ACMOtOt
1- Motorn
G1,n,e,1110J IM.
-G >n
-:-ocD r i v r-1
I SET Moto, I
Variation qfthe ap lied ooltage. This method is also called armature ooltage cont1'ol.
In a,mature voltage control method thespeed control is achieved by va,ying the applied voltage in the
.,,.,..,
SupJ)fv
armature winding of the motor.
TI1is speed control method is also known
as Ward Leonard Method. This method
was introduced in 1891.
0CMOI«
ACMOtOt
1- Motorn
G1,n,e,1110J IM.
-G >n
-:-ocD r i v r-1
I SET Moto, I
Speed control methods of DC shunt motor
Variation ofthe applied uoltage. This method is also called armature uoltage cont1'ol.
DC
C't«tMr;ttOr
OCMotot
♦
v,
ACMotor
in..
I ♦ - n I
1-
l
MotorG t o r t M •<i>-----:-oc Drive-
SU t Motor I
ln the above system, M is the main DC motor whose
speed is to b-eontrolled, and Gis a separatelyexcited
DCgenerator.
The generator G is driven bya 3 phase driving motor
which may be an induction motor or a synchronous
motor.
'fl1e combination of an AC driving motor and the DC
generntor is called the Motor-Generator CM-G) set.
The voltage of the generatoi· is changed by changing the
generator field current. 'fltis voltage when direcUyapplied
to t:he armature of the main DC motor, the speed of the
motor Mchanges.
The motor field current lrmis kept constant so that the motor
field flux 9., also remains constant. While Uie speed of U1e
motor is controlled, the motor armature current la is kept
equal to its ratedvalue.
Variation ofthe applied uoltage. This method is also called armature uoltage cont1'ol.
DC
C't«tMr;ttOr
OCMotot
♦
v,
ACMotor
in..
I ♦ - n I
1-
l
MotorG t o r t M •<i>-----:-oc Drive-
SU t Motor I
ln the above system, M is the main DC motor whose
speed is to b-eontrolled, and Gis a separatelyexcited
DCgenerator.
The generator G is driven bya 3 phase driving motor
which may be an induction motor or a synchronous
motor.
'fl1e combination of an AC driving motor and the DC
generntor is called the Motor-Generator CM-G) set.
The voltage of the generatoi· is changed by changing the
generator field current. 'fltis voltage when direcUyapplied
to t:he armature of the main DC motor, the speed of the
motor Mchanges.
The motor field current lrmis kept constant so that the motor
field flux 9., also remains constant. While Uie speed of U1e
motor is controlled, the motor armature current la is kept
equal to its ratedvalue.
Speed control methods of DC shunt motor
Variation ofthe ap lied ooltage. This method isalso called armature ooltage cont1'ol.
)P
,
h
,
1.
H..
A.
.C
oc
CitMfl'tOt
DCMoco,
+
v,
ACMotor
'111e generated field current lrg is varied such tliatthe
armature voltage v, changes from zero to its rated
value. The speed will change from zero to the base
speed.
Since the speed control is carried out with the rated
current la and with the constant motor field Oux, a
constant torque is directly proportional to the
armature current, and field flux up to rated speed is
obtained.
·n1e product of torque and speed is known as power, and it
is proportional to speed. Thus, with the increase io power,
speed i11creases automatically.
Variation ofthe ap lied ooltage. This method isalso called armature ooltage cont1'ol.
)P
,
h
,
1.
H..
A.
.C
oc
CitMfl'tOt
DCMoco,
+
v,
ACMotor
'111e generated field current lrg is varied such tliatthe
armature voltage v, changes from zero to its rated
value. The speed will change from zero to the base
speed.
Since the speed control is carried out with the rated
current la and with the constant motor field Oux, a
constant torque is directly proportional to the
armature current, and field flux up to rated speed is
obtained.
·n1e product of torque and speed is known as power, and it
is proportional to speed. Thus, with the increase io power,
speed i11creases automatically.
Speed control methods of DC shunt motor
Variation qfthe applied ooltage. This method is also called armature ooltage cont1'ol.
Advantages of Ward Leonard Drives
Smooth speed control of DCmotorover a wide range in both thedirection is possible.
It has an inherent braking capacity.
Uniform acceleration is obtained
Disadvantages ofWard Leonard Drives
Larger size and weight.
The initial cost of the system is high as there isa motor-generator set installed, of the same rating as thatof
the main DC motor.
Maintenance of the system isfrequent.
Higher losses and less efficiency.
Variation qfthe applied ooltage. This method is also called armature ooltage cont1'ol.
Advantages of Ward Leonard Drives
Smooth speed control of DCmotorover a wide range in both thedirection is possible.
It has an inherent braking capacity.
Uniform acceleration is obtained
Disadvantages ofWard Leonard Drives
Larger size and weight.
The initial cost of the system is high as there isa motor-generator set installed, of the same rating as thatof
the main DC motor.
Maintenance of the system isfrequent.
Higher losses and less efficiency.
Speed control methods of DC shunt motor
Variation qfthe applied ooltage. This method is also called armature ooltage control.
A_pplications ofWard Leonard Drives
·me Ward Leonard drives are used where smooth speed control of the DC motors over a wide range in both
the diredfons is required. Some of the examples are as follows:
Rolling mills
Elevators
Cranes
Paper mills
Diesel-electric locomotives
Mine hoists
Variation qfthe applied ooltage. This method is also called armature ooltage control.
A_pplications ofWard Leonard Drives
·me Ward Leonard drives are used where smooth speed control of the DC motors over a wide range in both
the diredfons is required. Some of the examples are as follows:
Rolling mills
Elevators
Cranes
Paper mills
Diesel-electric locomotives
Mine hoists
Reversal of direction of rotation of DC motor
DC motors can tum in either direction (clockwise or co11nter-clockwise) and can be easily controlled by
inve,ting the polarity of theapplied voltage.
TI1e direction of force, and therefore rotation, is explained using Fleming's Left-Hand Rule for Motors.
North
South
Your first finger1-epresents the magnetic
field, pointing straightdown to the floor.
Your middle finger represents the
ct1rrent, pointing towards the
computer sc1-een.
Your thumb represents the 1-esulting
force, which points left.
TI1is shows us that with the current Oowing through the wire ••in1o"U1e computer screen will cause a force
pushing left, in our model, this isequivalent to the motor turning counter-clockwise.
DC motors can tum in either direction (clockwise or co11nter-clockwise) and can be easily controlled by
inve,ting the polarity of theapplied voltage.
TI1e direction of force, and therefore rotation, is explained using Fleming's Left-Hand Rule for Motors.
North
South
Your first finger1-epresents the magnetic
field, pointing straightdown to the floor.
Your middle finger represents the
ct1rrent, pointing towards the
computer sc1-een.
Your thumb represents the 1-esulting
force, which points left.
TI1is shows us that with the current Oowing through the wire ••in1o"U1e computer screen will cause a force
pushing left, in our model, this isequivalent to the motor turning counter-clockwise.
Reversal of direction of rotation of DC motor
howwe changethe force so the wire travels in the opposite dh'ection, causingour motor to rotatein'reverse',
We can use Fleming'sleft-hand ruleagain, with the samemagnetic field, but thistimeuseour thumbs to point
right instead of left. As a result, your middle finger should now point towards yourself, showing the current
flows out of the screen.
North
Flux !!! I cyrrent
Density.,..... o,_ut ofi;creen
South
This shows that in order to
make the motor rotate
clockwise, we must 1-everse
the flow of current (i.e.
changing the flow of current
changes the direction of the
force by 180 degrees).
Of course, the direction of current is controlled by the polarity of tbe voltage.
So inorder to change the direction of rotation, we cansimply reverse the voltage, causing the current to 0ow
in the opposite dh'ection, changing the force by 180 degrees and the motor to be driven 'bllckwards'.
howwe changethe force so the wire travels in the opposite dh'ection, causingour motor to rotatein'reverse',
We can use Fleming'sleft-hand ruleagain, with the samemagnetic field, but thistimeuseour thumbs to point
right instead of left. As a result, your middle finger should now point towards yourself, showing the current
flows out of the screen.
North
Flux !!! I cyrrent
Density.,..... o,_ut ofi;creen
South
This shows that in order to
make the motor rotate
clockwise, we must 1-everse
the flow of current (i.e.
changing the flow of current
changes the direction of the
force by 180 degrees).
Of course, the direction of current is controlled by the polarity of tbe voltage.
So inorder to change the direction of rotation, we cansimply reverse the voltage, causing the current to 0ow
in the opposite dh'ection, changing the force by 180 degrees and the motor to be driven 'bllckwards'.
Reversal of direction of rotation of DC motor
• -
...ue ,
•
Po$it1ve Polarity
C$ockwlse rotalion
-
mCu ,nl
Negative Polarity
Counter - Clockwfsa n>tation
s
FF
N
(•) •lb) (c) (d)
• -
...ue ,
•
Po$it1ve Polarity
C$ockwlse rotalion
-
mCu ,nl
Negative Polarity
Counter - Clockwfsa n>tation
s
FF
N
(•) •lb) (c) (d)
Reversal of direction of rotation of DC motor
It can be seen from the Fig. 2 that
F
N
F
<•l
•(bl (c) (d)
if the direction of the main field in which current carrying conductor is placed, is 1-eversed, force expe1ienced
by the conductor reverses its dil'ection (refer case a and c or b and d).
Similarly keeping main flttx direction unchanged, the direction of cun-ent passing through the t'Onductor is
reversed. The force experienced by the conductor reverses its di1-ection. (refer case a and b or c and d).
However if both the directions are reversed, the direction of the force experienced remains the same.
It can be seen from the Fig. 2 that
F
N
F
<•l
•(bl (c) (d)
if the direction of the main field in which current carrying conductor is placed, is 1-eversed, force expe1ienced
by the conductor reverses its dil'ection (refer case a and c or b and d).
Similarly keeping main flttx direction unchanged, the direction of cun-ent passing through the t'Onductor is
reversed. The force experienced by the conductor reverses its di1-ection. (refer case a and b or c and d).
However if both the directions are reversed, the direction of the force experienced remains the same.
Reversal of direction of rotation of DC motor
Soin a practical motor, to reverse its direction of rotation, either direction of main field produced bythe field
winding is reversed or dir<.>etion of the current passing through the armature is reversed.
TI1edirection of the main field can be reversed by changing the direction of cummt passing through the field
winding, which is possible by interchanging the polarities ofsupply which is given to the field winding.
Soin a practical motor, to reverse its direction of rotation, either direction of main field produced bythe field
winding is reversed or dir<.>etion of the current passing through the armature is reversed.
TI1edirection of the main field can be reversed by changing the direction of cummt passing through the field
winding, which is possible by interchanging the polarities ofsupply which is given to the field winding.
Braking in DC motor
A nmning motor may be brought to rest quickly by either mechanical braking or electrical braking.
Electrical Brakingis usually employed in applications tostopa unitdriven bymotors in an exact position or
to have the speed of the driven unit suitably controlled during its deceleration.
Electrical brakingis used in applications where frequent, quick, accurateor emergency stopsare required.
Electrical Braking allows smooth stops without any inconvenience to passengers.
When a loaded hoistis lowered, electric braking keeps tbespeedwithin safelimits. Otherwise, the machineor
chive speed will reach dangerousvalues.
When a train goes down a steep gradient, electric braking is employed to bold the trainspeed within the
prescribed safe limits.
Electrical Braking is more commonly used where active loads are applicable.
In spite of electric braking, the br-Jking force can also be obtained by using mechanical brakes.
A nmning motor may be brought to rest quickly by either mechanical braking or electrical braking.
Electrical Brakingis usually employed in applications tostopa unitdriven bymotors in an exact position or
to have the speed of the driven unit suitably controlled during its deceleration.
Electrical brakingis used in applications where frequent, quick, accurateor emergency stopsare required.
Electrical Braking allows smooth stops without any inconvenience to passengers.
When a loaded hoistis lowered, electric braking keeps tbespeedwithin safelimits. Otherwise, the machineor
chive speed will reach dangerousvalues.
When a train goes down a steep gradient, electric braking is employed to bold the trainspeed within the
prescribed safe limits.
Electrical Braking is more commonly used where active loads are applicable.
In spite of electric braking, the br-Jking force can also be obtained by using mechanical brakes.
Braking in DC motor
Disadvantages of Mechanical Braking
It requires frequent maintenance and replacement of brake shoes.
Braking power is wasted in the form of beat.
1)'pes orElectrical Braking:
Electrical Braking:
Regenerative
Braking
Dynamic or Plugging or
Rheostatic Braking Reverse Current Braking.
Disadvantages of Mechanical Braking
It requires frequent maintenance and replacement of brake shoes.
Braking power is wasted in the form of beat.
1)'pes orElectrical Braking:
Electrical Braking:
Regenerative
Braking
Dynamic or Plugging or
Rheostatic Braking Reverse Current Braking.
Regenerative Braking in DC shunt motor
In Regenerative Braking, the power or energy of the driven machinery which is in kinetic fo1111 is retu111ed
back 10 the power supply mains.
Amachineoperating as motor maygo into regenerative braking mode ifits speed becomes sufficiently highso
as to make back emf greater than the supply voltage i.e., Eb> V.
For armature winding circltit the equation will be given as:
+u
1,
Armature
J Shun!
Field
=□+□·'] ...
=□- ......(I)
w
Obviously under thiscondition the direction of I, will reverse imposing torque which is opposite to the
direction of rotation as Ta oc<l).Ja.
In Regenerative Braking, the power or energy of the driven machinery which is in kinetic fo1111 is retu111ed
back 10 the power supply mains.
Amachineoperating as motor maygo into regenerative braking mode ifits speed becomes sufficiently highso
as to make back emf greater than the supply voltage i.e., Eb> V.
For armature winding circltit the equation will be given as:
+u
1,
Armature
J Shun!
Field
=□+□·'] ...
=□- ......(I)
w
Obviously under thiscondition the direction of I, will reverse imposing torque which is opposite to the
direction of rotation as Ta oc<l).Ja.
Regenerative Braking in DC shunt motor
Plain lr'4ck whhoul gr11tfienl
E1, < V
Fig.(al Machine operates as motor
111equestion is howspeed on its own become large enough to m a k e < V causing regenerative braking.
Such a situation mayoccur in practice when the mechanical load itself becomes active.
r_, i ,_ - -- ..
TI1e situation is explained in figUl'es (a) and (b).
The normal motor operation is shown in figure (a)
where armature motoring current I, is drawn from
the supply and as usual Eb< V.
= •
Plain lr'4ck whhoul gr11tfienl
E1, < V
Fig.(al Machine operates as motor
111equestion is howspeed on its own become large enough to m a k e < V causing regenerative braking.
Such a situation mayoccur in practice when the mechanical load itself becomes active.
r_, i ,_ - -- ..
TI1e situation is explained in figUl'es (a) and (b).
The normal motor operation is shown in figure (a)
where armature motoring current I, is drawn from
the supply and as usual Eb< V.
= •
Regenerative Braking in DC shunt motor
,.
+o--.-------, Imagine the d.c motor is coupled to the wheel of
locomotive which is moving along a plain track
without anygradient as shown in figure (a).
Machine is running as a motor ata speed of n
I rpm.
Plain 1rack wi1hou1 gndicn1
E., < V
Fig. (a) Machine operates as motor
However, when the track has a downward gradient
(shown in figure b),component of gravitational force
Ir ♦
E,, > V
Track with gnadienl
Pig.(bl Machineenlers regenerative brakingmode.
along the track also appears which wiU try to
aci-elerate the motor and may increase itsspeed to n
2
such that e, = . 2 > .
In such a scenario, direction of la 1-everses, feeding
power back to supply.
Regenerative braking here wiU not stop the motor
butwill help to arrest rise ofdangerously high speed.
,.
+o--.-------, Imagine the d.c motor is coupled to the wheel of
locomotive which is moving along a plain track
without anygradient as shown in figure (a).
Machine is running as a motor ata speed of n
I rpm.
Plain 1rack wi1hou1 gndicn1
E., < V
Fig. (a) Machine operates as motor
However, when the track has a downward gradient
(shown in figure b),component of gravitational force
Ir ♦
E,, > V
Track with gnadienl
Pig.(bl Machineenlers regenerative brakingmode.
along the track also appears which wiU try to
aci-elerate the motor and may increase itsspeed to n
2
such that e, = . 2 > .
In such a scenario, direction of la 1-everses, feeding
power back to supply.
Regenerative braking here wiU not stop the motor
butwill help to arrest rise ofdangerously high speed.
Regenerative Braking in DC shunt motor
The na-essarycondition for regeneration is that the back EMF E,,should be greater than t·hesupply voltage so
that the a11nature current is reversed and the mocle of operation changes from motoring to generating.
Application. of Regenerati,•e Braking
Regenerative braking is usecl especially where frequent braking and slowing of drives is required.
It is most useful in holding a descending load of high potential energy at a -onstant speed.
Regenerative braking is used to control the speed of motors driving loads such as in electric
locomotives, elevators, cranes and hoists.
Regenerative braking cannot be used for stopping the motor. It is used for controlling the speed above
the no-load speed of the motor dri,>ing.
The na-essarycondition for regeneration is that the back EMF E,,should be greater than t·hesupply voltage so
that the a11nature current is reversed and the mocle of operation changes from motoring to generating.
Application. of Regenerati,•e Braking
Regenerative braking is usecl especially where frequent braking and slowing of drives is required.
It is most useful in holding a descending load of high potential energy at a -onstant speed.
Regenerative braking is used to control the speed of motors driving loads such as in electric
locomotives, elevators, cranes and hoists.
Regenerative braking cannot be used for stopping the motor. It is used for controlling the speed above
the no-load speed of the motor dri,>ing.
an
You
O.:p,irtnM:111of f.Jl'(1ronkTdt.-c:onumini.-.it1on Engg 8•
You
O.:p,irtnM:111of f.Jl'(1ronkTdt.-c:onumini.-.it1on Engg 8•
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