The document discusses various rules and principles related to DC machines, including Maxwell's Corkscrew Rule, Fleming's Left Hand Rule, Fleming's Right Hand Rule, Lenz's Law, the construction and working principles of DC generators and DC motors. It also covers types of DC generators and motors, methods of speed control for DC motors, and common applications of shunt, series, and compound DC motors.
This document discusses DC machines and provides details on various concepts related to DC generators and DC motors. It describes Maxwell's corkscrew rule and Fleming's left-hand and right-hand rules for determining magnetic fields and forces. It also explains Lenz's law, the construction and working principles of DC generators and motors, including their windings, commutation, and speed control methods. Various types of DC generators and motors are defined along with their characteristics and applications. Testing methods for determining efficiency of DC machines are also summarized.
This document discusses DC machines including Maxwell's corkscrew rule, Fleming's left and right hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes how DC generators convert mechanical energy to electrical energy using electromagnetic induction. It also explains how DC motors convert electrical energy to mechanical energy by producing torque on the armature windings when placed in a magnetic field. Various types of DC motors and methods for controlling motor speed are also summarized.
This document discusses DC machines and provides details on Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes how mechanical energy is converted to electrical energy in a DC generator through electromagnetic induction. DC motors are also summarized, explaining how they convert electrical energy to mechanical energy when a current-carrying conductor is placed in a magnetic field. Common applications of shunt, series, and compound DC motors are listed.
DC Machine Ppt. Presentation all rules and applicationSahilSk33
This document discusses DC machines and provides details on Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes commutation, armature reaction, speed control methods for DC motors using flux and armature voltage control, and testing of DC machines. Various types of DC generators and motors are discussed along with their applications.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
This document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, and brushes of DC machines. It also covers EMF equations, armature reaction, types of DC generators and motors, speed control methods, efficiency testing, and applications of shunt and series motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
This document discusses DC machines and provides details on various concepts related to DC generators and DC motors. It describes Maxwell's corkscrew rule and Fleming's left-hand and right-hand rules for determining magnetic fields and forces. It also explains Lenz's law, the construction and working principles of DC generators and motors, including their windings, commutation, and speed control methods. Various types of DC generators and motors are defined along with their characteristics and applications. Testing methods for determining efficiency of DC machines are also summarized.
This document discusses DC machines including Maxwell's corkscrew rule, Fleming's left and right hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes how DC generators convert mechanical energy to electrical energy using electromagnetic induction. It also explains how DC motors convert electrical energy to mechanical energy by producing torque on the armature windings when placed in a magnetic field. Various types of DC motors and methods for controlling motor speed are also summarized.
This document discusses DC machines and provides details on Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes how mechanical energy is converted to electrical energy in a DC generator through electromagnetic induction. DC motors are also summarized, explaining how they convert electrical energy to mechanical energy when a current-carrying conductor is placed in a magnetic field. Common applications of shunt, series, and compound DC motors are listed.
DC Machine Ppt. Presentation all rules and applicationSahilSk33
This document discusses DC machines and provides details on Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes commutation, armature reaction, speed control methods for DC motors using flux and armature voltage control, and testing of DC machines. Various types of DC generators and motors are discussed along with their applications.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
This document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, and brushes of DC machines. It also covers EMF equations, armature reaction, types of DC generators and motors, speed control methods, efficiency testing, and applications of shunt and series motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
This document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, and brushes of DC machines. It also covers EMF equations, armature reaction, types of DC generators and motors, speed control methods, efficiency testing, and applications of shunt and series motors.
This document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, and brushes of DC machines. It also covers e.m.f. equations, armature reaction, types of DC generators/motors, speed control methods, efficiency testing, and applications of shunt and series motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses DC machines and their components and operating principles. It describes Maxwell's corkscrew rule and Fleming's left-hand and right-hand rules for determining the direction of magnetic fields. It also explains Lenz's law governing induced electromotive force (emf). The key components of a DC generator are conductors, magnetic field, and a mechanical power source. It converts mechanical energy to electrical energy via electromagnetic induction. A DC motor operates on the same principles in reverse, using a current to generate motion.
Fleming's left hand rule is used to determine the direction of force acting on a current carrying conductor placed in a magnetic field. The middle finger represents the direction of current, the forefinger represents the direction of the magnetic field, and the thumb indicates the direction of the force acting on the conductor. This rule is used in motors. DC motors are used in applications requiring constant torque, rapid acceleration/deceleration, and responsiveness to feedback signals, such as electric vehicles, steel/aluminum mills, trains, cranes, and controls. DC motors consist of a commutator, armature, and field windings that generate a magnetic field to cause rotation.
This document provides reading material for electrical and electronics engineering students studying electrical machines II at RGPV affiliated colleges. It covers the syllabus for the unit on DC machines, including the basic construction of DC machines, types of excitation, armature and field windings, EMF equations, armature reaction and methods to limit it, commutation processes, performance of DC generators, and different types of DC motors like metadyne, amplidyne, permanent magnet, and brushless motors. The topics are explained over several pages with diagrams and examples. Key concepts covered are the magnetic circuits, armature and commutator construction, separately excited and self-excited machines, wave and lap windings, EMF equations, ar
The document discusses direct current (DC) machines, including their working principles, construction, and key components. It begins with an introduction and overview of Fleming's left-hand and right-hand rules for determining the direction of force on a current-carrying conductor in a magnetic field or induced electromotive force (emf) in a conductor. The working principle of a DC generator is then explained, where mechanical energy is converted to electrical energy using conductors and a magnetic field. Key parts of a DC machine like the field system, armature, commutator, and brushes are also described. Finally, the document concludes with references for further reading on electrical machines.
- DC machines can operate as either generators or motors. A generator produces voltage when its coil rotates through a magnetic field, while a motor produces torque on its coil when current passes through it in a magnetic field.
- The simplest DC machine is a single loop of wire rotating through magnetic poles. Induced voltage and torque depend on flux, speed/current, and construction constants.
- Real DC machines use commutators and brushes to produce DC output from the AC voltage induced in the rotor coils. Problems during commutation like sparking are reduced by techniques like interpoles.
- The internal voltage and torque equations account for flux, speed/current, and construction constants. Power losses include copper, brush,
1) DC machines operate based on the principles that voltage is induced in a conductor moving through a magnetic field (generator action) and a force is induced on a conductor with current in a magnetic field (motor action).
2) The simplest DC machine is a single loop of wire rotating through magnetic poles, which induces a voltage that can be extracted using a commutator and brushes.
3) Real DC machines have more complex windings and commutation systems to produce a DC output and overcome issues like armature reaction.
4) The main types of DC generators - separately excited, shunt, and series - have different characteristics based on how their fields are connected that determine how voltage and current vary with load
1) DC generators convert mechanical energy to electrical energy through Faraday's law of electromagnetic induction. When a conductor moves through a magnetic field, an EMF is induced in the conductor.
2) The main components of a DC generator are the yoke, field electromagnets, armature, commutator, and brushes. The armature is wound with coils and rotates within the magnetic field produced by the field electromagnets to generate an EMF.
3) As the armature rotates, the commutator and brushes are used to periodically reverse the direction of current in the external circuit, thereby producing direct current. Losses in the generator arise from copper, iron, and mechanical components
1) DC generators convert mechanical energy to electrical energy through Faraday's law of electromagnetic induction. When a conductor moves through a magnetic field, an EMF is induced in the conductor.
2) The main components of a DC generator are the yoke, field electromagnets, armature, commutator, and brushes. The armature is wound with coils and rotates within the magnetic field produced by the field electromagnets to generate an EMF.
3) As the armature rotates, the commutator and brushes are used to periodically reverse the direction of current in the external circuit, thereby producing direct current. Losses in the generator arise from copper, iron, and mechanical components
The document discusses the key concepts of induction motors. It explains that an induction motor operates by using a rotating magnetic field in the stator to induce currents in the rotor that generate torque. It describes the different components of an induction motor including the squirrel cage and wound rotors. It also discusses important concepts like slip speed, synchronous speed, rotor frequency, equivalent circuits, power flow, and how torque is developed based on the interaction between stator and rotor magnetic fields.
DC generators convert mechanical energy to electrical energy using electromagnetic induction. They have a stationary part that produces a magnetic field and a rotating part called the armature. As the armature rotates in the magnetic field, a current is induced based on Faraday's law of induction. The commutator ensures the current flows in one direction to the load. The main parts are the magnetic frame, field coils, armature core and windings, commutator and brushes. The types of DC generators are separately excited, shunt, series and compound wound which differ in how the field and armature windings are connected. They have various applications including battery charging, motor operation, and power distribution.
DC machines operate using electromagnetic induction and include generators and motors. A DC generator converts mechanical energy to electrical energy using a magnetic field and conductors that rotate inside the field. Key components of a DC generator include an armature winding on a core that rotates inside stationary field windings, producing an induced current via Faraday's law of induction. The direction of the induced electromotive force is determined by Fleming's right hand rule.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
This document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, and brushes of DC machines. It also covers EMF equations, armature reaction, types of DC generators and motors, speed control methods, efficiency testing, and applications of shunt and series motors.
This document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, and brushes of DC machines. It also covers e.m.f. equations, armature reaction, types of DC generators/motors, speed control methods, efficiency testing, and applications of shunt and series motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses various topics related to DC machines including Maxwell's corkscrew rule, Fleming's left-hand and right-hand rules, Lenz's law, the construction and working principles of DC generators and motors. It describes the field system, armature, commutator, brushes, and winding types in DC machines. It also covers EMF equations, characteristics, speed control methods, losses, testing, and applications of DC generators and motors.
The document discusses DC machines and their components and operating principles. It describes Maxwell's corkscrew rule and Fleming's left-hand and right-hand rules for determining the direction of magnetic fields. It also explains Lenz's law governing induced electromotive force (emf). The key components of a DC generator are conductors, magnetic field, and a mechanical power source. It converts mechanical energy to electrical energy via electromagnetic induction. A DC motor operates on the same principles in reverse, using a current to generate motion.
Fleming's left hand rule is used to determine the direction of force acting on a current carrying conductor placed in a magnetic field. The middle finger represents the direction of current, the forefinger represents the direction of the magnetic field, and the thumb indicates the direction of the force acting on the conductor. This rule is used in motors. DC motors are used in applications requiring constant torque, rapid acceleration/deceleration, and responsiveness to feedback signals, such as electric vehicles, steel/aluminum mills, trains, cranes, and controls. DC motors consist of a commutator, armature, and field windings that generate a magnetic field to cause rotation.
This document provides reading material for electrical and electronics engineering students studying electrical machines II at RGPV affiliated colleges. It covers the syllabus for the unit on DC machines, including the basic construction of DC machines, types of excitation, armature and field windings, EMF equations, armature reaction and methods to limit it, commutation processes, performance of DC generators, and different types of DC motors like metadyne, amplidyne, permanent magnet, and brushless motors. The topics are explained over several pages with diagrams and examples. Key concepts covered are the magnetic circuits, armature and commutator construction, separately excited and self-excited machines, wave and lap windings, EMF equations, ar
The document discusses direct current (DC) machines, including their working principles, construction, and key components. It begins with an introduction and overview of Fleming's left-hand and right-hand rules for determining the direction of force on a current-carrying conductor in a magnetic field or induced electromotive force (emf) in a conductor. The working principle of a DC generator is then explained, where mechanical energy is converted to electrical energy using conductors and a magnetic field. Key parts of a DC machine like the field system, armature, commutator, and brushes are also described. Finally, the document concludes with references for further reading on electrical machines.
- DC machines can operate as either generators or motors. A generator produces voltage when its coil rotates through a magnetic field, while a motor produces torque on its coil when current passes through it in a magnetic field.
- The simplest DC machine is a single loop of wire rotating through magnetic poles. Induced voltage and torque depend on flux, speed/current, and construction constants.
- Real DC machines use commutators and brushes to produce DC output from the AC voltage induced in the rotor coils. Problems during commutation like sparking are reduced by techniques like interpoles.
- The internal voltage and torque equations account for flux, speed/current, and construction constants. Power losses include copper, brush,
1) DC machines operate based on the principles that voltage is induced in a conductor moving through a magnetic field (generator action) and a force is induced on a conductor with current in a magnetic field (motor action).
2) The simplest DC machine is a single loop of wire rotating through magnetic poles, which induces a voltage that can be extracted using a commutator and brushes.
3) Real DC machines have more complex windings and commutation systems to produce a DC output and overcome issues like armature reaction.
4) The main types of DC generators - separately excited, shunt, and series - have different characteristics based on how their fields are connected that determine how voltage and current vary with load
1) DC generators convert mechanical energy to electrical energy through Faraday's law of electromagnetic induction. When a conductor moves through a magnetic field, an EMF is induced in the conductor.
2) The main components of a DC generator are the yoke, field electromagnets, armature, commutator, and brushes. The armature is wound with coils and rotates within the magnetic field produced by the field electromagnets to generate an EMF.
3) As the armature rotates, the commutator and brushes are used to periodically reverse the direction of current in the external circuit, thereby producing direct current. Losses in the generator arise from copper, iron, and mechanical components
1) DC generators convert mechanical energy to electrical energy through Faraday's law of electromagnetic induction. When a conductor moves through a magnetic field, an EMF is induced in the conductor.
2) The main components of a DC generator are the yoke, field electromagnets, armature, commutator, and brushes. The armature is wound with coils and rotates within the magnetic field produced by the field electromagnets to generate an EMF.
3) As the armature rotates, the commutator and brushes are used to periodically reverse the direction of current in the external circuit, thereby producing direct current. Losses in the generator arise from copper, iron, and mechanical components
The document discusses the key concepts of induction motors. It explains that an induction motor operates by using a rotating magnetic field in the stator to induce currents in the rotor that generate torque. It describes the different components of an induction motor including the squirrel cage and wound rotors. It also discusses important concepts like slip speed, synchronous speed, rotor frequency, equivalent circuits, power flow, and how torque is developed based on the interaction between stator and rotor magnetic fields.
DC generators convert mechanical energy to electrical energy using electromagnetic induction. They have a stationary part that produces a magnetic field and a rotating part called the armature. As the armature rotates in the magnetic field, a current is induced based on Faraday's law of induction. The commutator ensures the current flows in one direction to the load. The main parts are the magnetic frame, field coils, armature core and windings, commutator and brushes. The types of DC generators are separately excited, shunt, series and compound wound which differ in how the field and armature windings are connected. They have various applications including battery charging, motor operation, and power distribution.
DC machines operate using electromagnetic induction and include generators and motors. A DC generator converts mechanical energy to electrical energy using a magnetic field and conductors that rotate inside the field. Key components of a DC generator include an armature winding on a core that rotates inside stationary field windings, producing an induced current via Faraday's law of induction. The direction of the induced electromotive force is determined by Fleming's right hand rule.
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2. Maxwell’s Cork screw Rule :
Hold the cork screw in yr right
hand and rotate it in clockwise
in such a way that it advances in
the direction of current. Then
the direction in which the hand
rotates will be the direction of
magnetic lines of force .
4. Fleming’s left hand rule
Used to determine the direction of force acting
on a current carrying conductor placed in a
magnetic field .
The middle finger , the fore finger and thumb of
the left hand are kept at right angles to one
another .
The middle finger represent the direction
of current
The fore finger represent the direction of
magnetic field
The thumb will indicate the direction of
force acting on the conductor .
This rule is used in motors.
6. Fleming’s Right hand rule
Used to determine the direction of emf induced
in a conductor
The middle finger , the fore finger and thumb of
the left hand are kept at right angles to one
another.
The fore finger represent the direction
of magnetic field
The thumb represent the direction of
motion of the conductor
The middle finger will indicate the
direction of the inducted emf .
This rule is used in DC Generators
7. Len’s Law
The direction of induced emf is given by
Lenz’s law .
According to this law, the induced emf will
be acting in such a way so as to oppose the
very cause of production of it .
e = -N (dØ/dt) volts
8. DC Generator
Mechanical energy is converted to electric
energy
Three requirements are essential
1. Conductors
2. Magnetic field
3. Mechanical energy
9. Working principle
A generator works on the principles of
Faraday’s law of electromagnetic induction
Whenever a conductor is moved in the
magnetic field , an emf is induced and the
magnitude of the induced emf is directly
proportional to the rate of change of flux
linkage.
This emf causes a current flow if the
conductor circuit is closed .
18. Armature winding
There are 2 types of winding
Lap and Wave winding
Lap winding
A = P
The armature
windings are
divided into
no. of sections
equal to the no
of poles
Wave winding
A = 2
It is used in low
current output
and high voltage.
2 brushes
19. Field system
It is for uniform magnetic field within
which the armature rotates.
Electromagnets are preferred in
comparison with permanent magnets
They are cheap , smaller in size ,
produce greater magnetic effect and
Field strength can be varied
21. Armature core
The armature core is cylindrical
High permeability silicon steel
stampings
Impregnated
Lamination is to reduce the eddy
current loss
22. Commutator
Connect with external circuit
Converts ac into unidirectional current
Cylindrical in shape
Made of wedge shaped copper segments
Segments are insulated from each other
Each commutator segment is connected to
armature conductors by means of a cu strip called
riser.
No of segments equal to no of coils
23. Carbon brush
Carbon brushes are used in DC machines
because they are soft materials
It does not generate spikes when they contact
commutator
To deliver the current thro armature
Carbon is used for brushes because it has
negative temperature coefficient of resistance
Self lubricating , takes its shape , improving
area of contact
25. Carbon brush
Brush leads (pig tails)
Brush rocker ( brush gear )
Front end cover
Rear end cover
Cooling fan
Bearing
Terminal box
26. EMF equation
Flux cut by 1 conductor
in 1 revolution = P * φ
Flux cut by 1 conductor in
60 sec = P φ N /60
Avg emf generated in 1
conductor = PφN/60
Number of conductors in
each parallel path = Z /A
Eg = PφNZ/60A
27. DC generators are generally classified
according to their method of excitation .
Separately excited DC generator
Self excited D C generator
Types of DC Generator
28. Further classification of DC Generator
Series wound generator
Shunt wound generator
Compound wound generator
Short shunt & Long shunt
Cumulatively compound
&
Differentially compound
29. Losses in DC Generators
1. Copper losses or variable losses
2. Stray losses or constant losses
Stray losses : consist of (a) iron losses or core
losses and (b) windage and friction losses .
Iron losses : occurs in the core of the machine
due to change of magnetic flux in the core .
Consist of hysteresis loss and eddy current
loss.
Hysteresis loss depends upon the frequency ,
Flux density , volume and type of the core .
30. Losses
Hysteresis loss depends upon the frequency ,
Flux density , volume and type of the core .
Eddy current losses : directly proportional to
the flux density , frequency , thickness of the
lamination .
Windage and friction losses are constant due to
the opposition of wind and friction .
31. Shunt Generators:
a. in electro plating
b. for battery recharging
c. as exciters for AC generators.
Applications
Series Generators :
A. As boosters
B. As lighting arc lamps
32. DC Motors
Converts Electrical energy into Mechanical
energy
Construction : Same for Generator and
motor
Working principle : Whenever a current
carrying conductor is placed in the
magnetic field , a force is set up on the
conductor.
33. Back emf
The induced emf in the rotating armature
conductors always acts in the opposite
direction of the supply voltage .
According to the Lenz’s law, the direction of the
induced emf is always so as to oppose the
cause producing it .
In a DC motor , the supply voltage is the cause
and hence this induced emf opposes the
supply voltage.
34. Classification of DC motors
DC motors are mainly classified into
three types as listed below:
Shunt motor
Series motor
Compound motor
Differential compound
Cumulative compound
35. According to the speed equation of a dc motor
N ∞ Eb/φ
∞ V- Ia Ra/ φ
Thus speed can be controlled by-
Flux control method: By Changing the flux by
controlling the current through the field
winding.
Armature control method: By Changing the
armature resistance which in turn changes
the voltage applied across the armature
Speed control of DC motors
36. Advantages of flux control:
It provides relatively smooth and easy control
Speed control above rated speed is possible
As the field winding resistance is high the field current
is small. Power loss in the external resistance is small .
Hence this method is economical
Disadvantages:
Flux can be increased only upto its rated value
High speed affects the commutation, motor operation
becomes unstable
Flux control
37. Armature voltage control method
The speed is directly proportional to the voltage
applied across the armature .
Voltage across armature can be controlled by
adding a variable resistance in series with the
armature
Potential divider control :
If the speed control from zero to the rated speed is
required , by rheostatic method then the voltage
across the armature can be varied by connecting
rheostat in a potential divider arrangement .
38. Starters for DC motors
Needed to limit the starting current .
1. Two point starter
2. Three point starter
3. Four point starter