The inverter is a static device. It can convert one form of electrical power into other forms of electrical power. But it cannot generate electrical power. Hence the inverter is a converter, not a generator.
The inverter is a static device. It can convert one form of electrical power into other forms of electrical power. But it cannot generate electrical power. Hence the inverter is a converter, not a generator.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Nowadays, it is very important to maintain voltage level. Controlling of that voltage is also important. This Presentation contains methods of voltage control.
INTRODUCTION
A chopper is a static device which is used to obtain a variable dc voltage from a
constant dc voltage source. A chopper is also known as dc-to-dc converter. The thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control. Choppers are widely used in trolley cars, battery operated vehicles, traction motor control, control of large number of dc motors, etc….. They are also used in regenerative braking of dc motors to return energy back to supply and also as dc voltage regulators.
Choppers are of two types
• Step-down choppers
• Step-up choppers.
In step-down choppers, the output voltage will be less than the input voltage
whereas in step-up choppers output voltage will be more than the input voltage.
Classification of Choppers:
(a) Depending upon the direction of the output current and voltage, the converters can be classified into five classes namely Class A [One-quadrant Operation] Class B [One-quadrant Operation] Class C [Two-quadrant Operation] Class D [Two-quadrant Operation] Class E [Four-quadrant Operation]
(b) Based on the output voltage of the output, the choppers are classified as
(i) Step-Down Chopper In this case the average output voltage is less than the input voltage. It is also known as step down converter
(ii) Step-Up Chopper Here the average output voltage is more than the input voltage. It is also known as step up converter
(iii) Step-Up/Down Chopper This type of converter produces an output voltage that is either lower or higher than the input voltage
(c) Depending upon the power loss occurred during turn ON/OFF of the switching device, the choppers are classified into two categories namely
(i) Hard switched Converter Here the power loss is high during the switching (ON to OFF and OFF to ON) as a result of the non zero voltage and current on the power switches.
(ii) Soft switched or resonant converters In this type of choppers, the power loss is low at the time of switching as a result of zero voltage and/or zero current on the switches.
2
PRINCIPLE OF STEP-DOWN CHOPPER
Figure 2.1 shows a step-down chopper with resistive load. The thyristor in the
circuit acts as a switch. When thyristor is ON, supply voltage appears across the load and
when thyristor is OFF, the voltage across the load will be zero. The output voltage and
current waveforms are as shown in figure 2.2.
This ppt gives the basic idea about multilevel inverter.this ppt includes
1.Introduction
2.Advantages of multilevel inverters
3.Types of multilevel inverters
4.Working of multilevel inverters
5.Applications.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Nowadays, it is very important to maintain voltage level. Controlling of that voltage is also important. This Presentation contains methods of voltage control.
INTRODUCTION
A chopper is a static device which is used to obtain a variable dc voltage from a
constant dc voltage source. A chopper is also known as dc-to-dc converter. The thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control. Choppers are widely used in trolley cars, battery operated vehicles, traction motor control, control of large number of dc motors, etc….. They are also used in regenerative braking of dc motors to return energy back to supply and also as dc voltage regulators.
Choppers are of two types
• Step-down choppers
• Step-up choppers.
In step-down choppers, the output voltage will be less than the input voltage
whereas in step-up choppers output voltage will be more than the input voltage.
Classification of Choppers:
(a) Depending upon the direction of the output current and voltage, the converters can be classified into five classes namely Class A [One-quadrant Operation] Class B [One-quadrant Operation] Class C [Two-quadrant Operation] Class D [Two-quadrant Operation] Class E [Four-quadrant Operation]
(b) Based on the output voltage of the output, the choppers are classified as
(i) Step-Down Chopper In this case the average output voltage is less than the input voltage. It is also known as step down converter
(ii) Step-Up Chopper Here the average output voltage is more than the input voltage. It is also known as step up converter
(iii) Step-Up/Down Chopper This type of converter produces an output voltage that is either lower or higher than the input voltage
(c) Depending upon the power loss occurred during turn ON/OFF of the switching device, the choppers are classified into two categories namely
(i) Hard switched Converter Here the power loss is high during the switching (ON to OFF and OFF to ON) as a result of the non zero voltage and current on the power switches.
(ii) Soft switched or resonant converters In this type of choppers, the power loss is low at the time of switching as a result of zero voltage and/or zero current on the switches.
2
PRINCIPLE OF STEP-DOWN CHOPPER
Figure 2.1 shows a step-down chopper with resistive load. The thyristor in the
circuit acts as a switch. When thyristor is ON, supply voltage appears across the load and
when thyristor is OFF, the voltage across the load will be zero. The output voltage and
current waveforms are as shown in figure 2.2.
This ppt gives the basic idea about multilevel inverter.this ppt includes
1.Introduction
2.Advantages of multilevel inverters
3.Types of multilevel inverters
4.Working of multilevel inverters
5.Applications.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
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Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Pile Foundation by Venkatesh Taduvai (Sub Geotechnical Engineering II)-conver...
RGPV Unit i ex503 - copy
1. READING MATERIAL FOR B.E STUDENTS
OF RGPV AFFILIATED
ENGINEERING COLLEGES PERSUING IN
ELECTRICAL AND ELECTRONICS BRANCH
Professor MD Dutt
Addl General Manager (Retd)
BHARAT HEAVY ELECTRICALS LIMITED
Professor(ex) in EX Department
Bansal Institute of Science and Technology
KOKTA ANANAD NAGAR BHOPAL
Presently Head of The Department ( EX)
Shri Ram College Of Technology
Thuakheda BHOPAL
Sub Code Ex503 Subject Electrical Machine II
UNIT I DC Machines I
2. RGPV Syllabus
EX 503 ELECTRICAL MACHINES II
UNIT I
DC MACHINES I
Basic construction of DC machines, Types of DC machines and method of excitation,
lap and wave winding, EMF equation; armature reaction and methods of limiting
armature reaction; Commutation process and methods for improving commutation;
Basic performance of DC generators and their performance characteristics; Metadyne
and amplidyne; permanent magnet DC motor; Brushless DC motor
INDEX
S No Topic Page
1 Basic construction of DC machines 2,3,4
2 Types of DC machines and method of excitation 5,6,7
3 Lap and wave winding, EMF equation 7,8
4 Armature reaction and methods of limiting armature reaction 9,10,11,12
5 Commutation process and methods for improving commutation 12,13,14,15
6 Basic performance of DC generators and their performance
characteristics
15,16,17,18,
7 Metadyne and Amplidyne; 19,20,21
8 Permanent magnet DC motor 21,22
9 Brushless DC motor 23,24,25,26
10 27
3. Q1 Write down the magnetic field system for a D.C. machine?
Ans:- The magnetic field system is the stationary (FIXED ) part of the
machine. It produces the main magnetic flux. The outer frame or yoke is a
hollow cylinder of cast steel or rolled steel. An even number of pole cores
are bolted to the yoke, he yoke serves following purpose:-
a).it supports the pole cores and acts as a protecting cover to the machine.
b) It forms a part of the magnetic circuit.
Each pole cores have pole shoe having curved surface it serves:
i) It supports field coils
4. ii) It increases the cross sectional area of magnetic circuit and reduces
reluctance.
The pole cores are made of silicon sheet steel laminations that are
insulated from each other by thin layer of varnish and are riveted
together.
Each pole core have one or more field coils placed over it to produce
magnetic field
Q2 Explain with neat diagram armature of a DC machine?
Ans The rotating part of the D.C machine is called the armature. The
armature consists of a shaft on which a laminated cylinder, called
armature core, is mounted with help of a key for small machines and for
large machines they are mounted on a spider. The armature laminations
are having slots on the outer surface. The laminations are insulated from
each other and tightly clamped together. The purpose of using laminated
core is to reduce the eddy current loss.
The insulated conductors are put in the slots of the armature core. The
conductors are wedged and bands of steel wire is used to prevent them
flying under centrifugal forces. The conductors are connected together.
The connection arrangement is called armature wining ( LAP AND
5. WAVE)
Q3 Construction of Commutator
Ans:- Alternating voltage is induced in the coil rotating magnetic field.
To obtain direct current in the external circuit a commutator is needed.
The commutator rotates with the armature. The commutator is made from
wedge shaped hard drawn silver bearing copper segments. The each
segments are insulated from each other by mica and the inner surface is
also insulated from shaft. The riser of the commutator is connected to the
ends of the armature conductors
The current is collected from armature winding by means of two or more
car4bon brushes mounted on the commutator. Each brush is supported in
the brush holders. Brush holders are mounted on the brush gear. It
connects the stationary circuit to rotating circuit of armature.
6. Q4 Separately excitated DC machine.
Ans:- There are two type of excitation , namely separately excited and
self excited machine.
he seethe field coils are energized by a separate DC source. The
connections showing the separately excited d.c. machine is shown here
below.
Separately-excited generators are those whose field magnets are
energised from an independent external source of d.c. current.
Q5 Series wound DC motor or Generator?
Ans Self-excited generators are those whose field magnets are
energised by the current produced
by the generators themselves. Due to residual magnetism, there is
always present some flux in the poles. When the armature is rotated,
some e.m.f. and hence some induced current is produced which is partly or
fully passed through the field coils thereby strengthening the residual pole
flux.
7. Three types of self-excited DC Motors or Generators are there
Shunt wound
The field windings are connected across or in parallel with the armature
conductors and have the full voltage of the generator applied across them
Series Wound
the field windings are joined in series with the armature conductors
Q6 Compound wound DC Machines
Compound Wound
It is a combination of a few series and a few shunt windings and
can be either short-shunt or long-shunt
8. Q 7 What do you mean by WAVE and LAP Winding
Ans Armature coils can be connected to the riser of commutator to
form either LAP or WAVE winding
WAVE WINDING
9. The ends of each armature coils are connected to commutator
Segment some distance apart, so that only two parallel paths are
provided between the positive and negative brushes. Thus wave
wound machines have A=2, They are used for High voltage low
current machines
LAP WINDING The ends of each armature coil is connected to
adjacent segments on the commutator so that total number of parallel
path is equal to the total number pf poles, Thus for LAP A=P The Lap
winding is used for low voltage high current machines.
Q8 Derive E.M.F equation of a Dc Machine
Ans Generated E.M.F. or E.M.F. Equation of a Generator
Eg = PNZ/60a
Where:
Φ = flux/pole in weber
Z = total number of armature conductors
P = No. of generator poles
a = No. of parallel paths in armature
N = armature rotation in revolutions per minute (r.p.m.)
E = e.m.f. induced in any parallel path in armature Generated e.m.f.
Eg = e.m.f. generated in any one of the parallel paths i.e. E.
10. Q9 What do you mean by armature reaction:
Ans All current-carrying conductors produce magnetic fields. The
magnetic field produced by current in the armature of a DC generator
affects the flux pattern and distorts the main field. This distortion
causes a shift in the neutral plane, which affects commutation. This
change in the neutral plane and the reaction of the magnetic field is
called ARMATURE REACTION
Armature reaction can be better understood with this figure:-
UNDESIRABLE EFFECTS OF ARMATURE REACTION
1. Armature reaction causes a net reduction in the field flux per
pole. Due to this net flux decrease, induced armature e.m.f.
decreases and also the torque decreases.
2. Distortion of the main field flux along the air gap i.e. MNA
axis shifted. Due to this there is a problem of commutation
which results in copper losses, iron losses, sparking etc.
Q 10 Methods How to minimize armature reaction
Ans : Methods To Reduce Armature Reaction
By high Reluctance at POLE TIPS:
11. 1. At the time of construction we use chamfered poles. These poles
have larger air gap on the tips and smaller air gap at the centre.
These poles provide non-uniform air gap. The effect of armature
reaction is more near to edge of poles and negligible near the
centre of pole.
If air gap is kept non uniform i.e., larger air gap at the edges(Pole
Tip) and smaller near the centre of the pole and then armature flux
near the pole tip decreases and armature reaction decreases.
2. By Laminated Pole Shoe:
We insert Laminated objects in the pole. By having Laminated
pole shoe the reluctance in the armature flux path increases.
Hence the armature flux gap gets reduced
3. By Reduction in Armature flux:
The effect of Armature Reaction is reduced by creating more
reluctance in the path of Armature flux. This is achieved by using
field Pole Laminations having several Rectangular holes punched
in them. It gives high Reluctance in the path of armature flux. Due
12. to this armature cross flux reduces whereas main field remains
almost unaffected.
4. By having Strong main magnetic field:
During the design of DC machine it should be ensured that the
main field m.m.f. is sufficiently strong in comparison with full
load armature flux.
Greater the main field, lesser will be the distortion.
5) By using Inter Poles and Compensating Windings
The effect of Armature reaction is reduced by interpoles placed in
between the main poles. The magnetic axis of interpoles is in the
Direction of q-axis. Interpoles windings are connected in series
with the armature winding. So that, interpoles flux is able to
neutralize the effect of armature flux. The interpoles are narrow
and tapered with large air gap.
Interpoles are added [NN & SS]
13. The Armature Reaction can also be limited by compensating
windings. It is the best and most expensive methods. The
compensating windings are connected in series with armature
winding.
Q11 What is commutation How it can be improve
14. In the armature conductors of a d c generator are alternating in nature .
The commutations process involves the change from a generated alternating current to
an externally applied direct current . These induced current flow in one direction when
the armature conductor are under north pole . They are in opposite direction when they
are under south pole . As conductor pass out of the influence of north pole and enter
the south pole , the current in them is reversed . The reversible of current takes place
along the MNA or brush axis . When ever a brush spans two commutater segments ,
the winding element connect to those segments is short circuited . By commutation we
mean the change that takes in a winding element during the period of short circuit by a
brush. These changes are shown in figure.
In position (a)The current I flowing towards the brush from L.H.S passes round the
coil in a clockwise direction
In position (b), this coil carries the same current in the same direction, but the coil is to
short circuited by brush
In the position (c) the brush makes contact with bars a and b, thereby short circuiting
coil 1.The current is still I from L.H.S and I from R.H.S.
It is seen that these two currents can reach the brush without passing through coil 1
In (d) shows that bar b has just left the brush and the short circuit of coil1 has ended. It
is now necessary for the current I reaching the brush from the R.H.S in the
anticlockwise direction.
It is seen from above that during the period of short circuit of an armature coil by a
brush the current in that coil must be reversed and also brought up to its full value in
the reversed direction. The time of short circuit is known as period of commutation.
METHODS OF IMPROVING COMMUTATION
There are three methods for getting sparkles commutation.
1. Resistance commutation
2. Voltage commutation
3. Compensating winding
Resistance commutation
15. The method of improving commutation consists of using carbon brushes . This
makes the contact resistance between the commutator segment and brushes high.
This high contact resistance has tendency to force the current in the short
circuited coil to change according to the commutation requirements.
Voltage commutation
In this method arrangement is made to induce a voltage in the coil under going
commutation , which will neutralize the reactance voltage. The injected voltage
is in opposition to the reactance voltage and if the value of injected voltage is
made equal to reactance voltage ,quick reversal of current in the short circuited
coil will take place and there will be sparkles commutation.
a)Brush Shift
The effect of armature reaction is to shift the MNA in the direction of rotation in
case of generator and against the MNA in case of Motor.
b) Commutating or Inter poles
Interpoles are narrow poles attached to the stator yoke, and placed exactly
midway between the main poles. The compole windings are connected in series
with the armature, because the interpoles must produce fluxes that are directly
proportional to the armature current
The armature and interpole mmf’s are affected simultaneously by the same
armature current. Consequently the armature flux which tends to shift the MNA
is neutralized. The interpoles must induce a voltage in the conductors
undergoing commutation that is opposite to the voltage caused by the neutral
plane shift and reactance voltage.
i)For a generator, the polarity of the interpole must be the same as that of the
next main pole further ahead in the direction of rotation.
ii) For a motor, the polarity of the interpole must be the opposite as that of the
next main pole in the direction of rotation.
16. COMPENSATING WINDINGS
Compensating windings are the most effective way for eliminating the problem
of armature reaction and flash over by balancing armature mmf. The
compensating windings are placed in the pole faces parallel to the rotor armature
conductors. These windings are connected in series with the armature windings.
The compensating winding produces an mmf that is equal and opposite to the
armature mmf.
The major draw back with compensating winding is that they are very costly.
There use can be justified for the following special cases
a) In large machines subject to heavy overloads or plugging
b) In small motors subject to sudden reversal and high acceleration.
Q12 Draw the characteristics of a separately and shunt excited DC
generator
In general, three characteristics specify the steady-state performance of a DC
generators:
1. Open-circuit characteristics: generated voltage versus field current at constant
speed. This is also called magnetizing characteristics
2. Internal characteristic: It is plot between generated voltage versus load current
17. 3. External characteristic or Load characteristic: terminal voltage load current at
constant speed.
The terminal voltage of a dc generator is given by
Open-circuit and load characteristics separately excited DC generator
It can be seen from the external characteristics that the terminal voltage falls
slightly as the load current increases. Voltage regulation is defined as the
percentage change in terminal voltage when full load is removed, so that from
the external characteristics,
aa
mf
aaat
RI
dropreactionArmatureIf
RIEV
,
100
t
ta
V
VE
regulationVoltage
18. EXTERNAL CHRACTERISTICS
Self-Excited DC Shunt Generator
Maximum permissible value of the field resistance if the terminal voltage has to
build up. OPEN CIRCUIT CHARACTERISTICS
19. Q13 Basic performance of DC Generator what are main characteristics
Since the field current If in a shunt generator is very small the voltage drop IfRa can be
neglected and
V=Ea V=If Rf is a straight line and is called resistance line the figure gives below
the voltage build up in DC shunt generator for various field circuit resistance. A
decrease in resistance of the field circuit reduces the slope of the field resistance line
resulting in higher voltage. If the speed is constant An increase in the resistance of the
field circuit increases the slope of the field resistance line, resulting lower voltage If
the field resistance is increased to Rc which is termed as the critical resistance of the
field, the field resistance line becomes tangent to the initial part of the magnetizing
curve, when the field resistance is higher than this value, the generator fails to excite .
The figure above shows the variation of no load voltage with fixed Rf and variable
speed of the armature. The magnetizing curve varies with the speed and its ordinate for
any field current is proportional to the speed of the generator. The following conditions
must be satisfied for voltage build up
1. There must be sufficient residual flux in the field poles.
2. The field terminals should be such connected that the field current increases the
flux in direction of residual flux
3. The field circuit resistance should be less than the critical field resistance.
20. Characteristics of COPOUND DC GENERATOR
Depending upon the number of series field turns, the cumulatively compound
generators may be over compounded, flat compounded and under compounded.
For over compounded generator the full load terminal voltage is higher than No
load voltage, for flat compounded generator the full load terminal voltage is
equal to the no load voltage. In an under compounded generator the full load
terminal voltage is less than the no load voltage.
Q14 explain metadyne and amplydyne
21. An ordinary DC generator Can be modified to a matadyne by providing an additional
pair of brushes on D-axis as shown in figure. The quadrature axis(q axis) brushes are
short circuited and the output is
obtained from d axis brushes . The stator has control field winding , A current If
flows through the control field winding. When the generator is rotating at a constant
speed, the control field wing mmf, Ff induces an emf Eaq between the quadrature axis
brushes qq’, This emf is given by
Eaq = Kqf If
Where Kqf is constant If is the field current
Since the qq’ are short circuited, a quadrature axis armature current Iq flows and q axis
mmf Fq is established. Since the impedance of the short circuited path is low , only a
small control field current if will produce a much larger quadrature axis armature
current. Due to commutator action this magnetic field is stationary in space. An emf is
generated in the armature by its rotation in the quadrature axis flux, This emf appears
across the direct axis brushes dd’and is given by
Ead- KdqI q
Kdq is constant and I q is quadrature axis armature current
For a given Ff a load resistance steady values of Id and Iq are reached. Any increase in
Id reduces Eaq as seen by equation above this reduces Iq . Therefore Ead and Id are
reduced, hence for given value of control field excited current If the output current Id
remains substantially constant over a wide range load variation. That is a Metadyne
behave as constant current generator
AMPLIDYNE
The most common version of the matadyne is the amplidyne. The amplidyne consists
of the basic matadyne in which a compensating winding is connected in series with the
power output brush terminals. The d axis mmf which opposes the control field mmf in
matadyne is cancelled by the compensating winding . The compensating winding is
located in the d axis on the stator. The compensating winding carries the load current
Id and produces a flux which opposes the flux produced by the d axis armature current.
The negative feedback effect of the load current is therefore minimized .The d axis flux
22. now mainly depends on the field winding current. This gives a wider control over the
net d axis flux.
Q15 what do you mean by PMDC
A permanent magnet DC (PMDC) motor is the DC motor whose pole are made of
permanent magnets. Figure shows two pole PMDC motor. The permanent magnets of
the PMDC motor are radially magnetized and mounted on the inner periphery of
cylindrical steel stator. The stator also serves as the return path for the magnetic flux.
The rotor has conventional DC armature with commutator segments and brushes.
Most of the PMDC motors operates on 6V,12V or 24V dc supply obtained from
batteries or rectifiers.
The torque is produced by interaction between axial current carrying rotor conductors
and the magnetic flux produced by the permanent magnets. In a PMDC motor Flux
Φ is constant so the back EMF depends on
E=K1N
τ c= K1Ia
where K1 =K Φ is called speed voltage constant or torque constantt
V=E+IaRa
V = K1N +IaRa
23. N =(V-IaRa)/ K1
Advantages
1. There is no field circuit copper loss, this increases the efficiency
2. No space is required for field winding, these motors are smaller than
corresponding wound pole motors.
Disadvantages
1. There is risk of demagnetizing of poles may be caused by large armature current,
excessive heating
2. The magnetic field is always present even when motor is not in use, The motor
is totally enclosed so that foreign magnetic matter may not enter or get attracted
by PM.
3. The PM can produce high flux density as compare to externally supplied DC
shunt field . Therefore PMDC motor has lower induced torque compare to shunt
motor.
24. Q16 what is DC brushless motor
Ans Brushless DC Motor(BLDC)
Principles
• A BLDC is simply a normal dc motor turned inside out, that means the coil is
on the out side and the magnets are inside
• The stator consists of several coils which current is led through Creating a
magnetic field that makes the rotor turns
Construction
• Stator consists of stacked steel laminations with windings placed in
the slots that are axially cut along the inner periphery
• Rotor is made of permanent magnet and can vary from two to eight pole
pairs with alternate North (N) and South (S) poles. Ferrite magnets and
Rare earth alloy magnets are used in rotor
25. •
Unlike a brushed DC motor, the commutation of a BLDC motor is controlled
electronically.
• It is important to know the rotor position in order to understand which winding
will be energized following the energizing sequence.
• Rotor position is sensed by different ways some of them are
• 1)Hall sensors 2)Optical encoders
• :-When a magnetic field applied to a system with electric current a hall voltage
Perpendicular to the field and to current is generated. This was discovered by
Edwin Hall in 1879.
26. • Halls Sensors sense the position of
the coils The Decoder Circuit turns appropriate switches on and off The voltage
• through the specific coils turns the motor
• Torque speed characteristics of BLDC
ADVANTAGES
• Increased Reliability & Efficiency
• Longer Life
• Elimination of Sparks from Commutator
• Reduced Friction
• Faster Rate of Voltage & Current
DISADVANTAGES
27. • Requires Complex Drive Circuitry
• Requires additional Sensors
• Higher Cost
• Some designs require manual labor (Hand wound Stator Coils)
APPLICATION
• Consumer: Hard Drives, CD/DVD Drives, PC Cooling Fans, toys, RC airplanes,
air conditioners
• Medical: Artificial heart, Microscopes, centrifuges, Arthroscopic surgical tools,
Dental surgical tools and Organ transport pump system.