Generator hyder

SERIAL NAME ID DEPT.
1 MD. ISTIAQ AHMED 11105170 BSEEE
2 KM SHAHRIAR HYDER 11105040 BSEEE
3 MD. ABDULLAH AL MAHBUB 12205012 BSEEE
4 ROKONUZZAMAN 12105015 BSEEE
5 JOBAED HOSSAIN SUNY 11105188 BSEEE

We under went training program of 120 days from 5th
of January 2016 to 21st
of
April 2016 in EEN 257 (Machine- I). For this training program I would like to
thank M M Reazul Haque Tanmoy. Faculty of Electrical and Elkectronics
department in IUBAT- International University of Business Agriculture and
Technology, who arranged the training for us. And also I would like to thank
the whole faculty of the EEE department for their guidance and kind
supervision and filled confidence in us to go ahead in our life and face all
difficulties with courage.
                                                                                                             - ISTIAQ AHMED
                (Behalf of Group:1)

Context:
 1.Introduction to Generators.
 2.Principle of working.
 3.History of Generators.
 4.Types of Generators.
 5.AC Generator
 6.DC Generator
 7.Practical Generator.
 8.Generators in daily life.

1.Introduction to Generators
 The device which converts mechanical
energy to electrical energy is called generator
GENERATOR ELECTRICAL ENERGYMEHANICAL ENERGY

2.Principle of working:
 In generators mechanical energy is transformed
into electrical energy.
 The principle of all of the generators is same,
although the detail of construction may be differ
somewhat.
 A generator has two main parts:
 Coil
 Magnet

2.Principle of working:
 Generator works on
Faraday’s law of
electromagnetic
induction. When coil is
rotated in a magnetic
field by some
mechanical means
magnetic flux is
changed through the
coil and consequently
EMF is induced in the
coil.

3.History and evolution of
Generators
 Michel Faraday and Hippolyte Pixii were
pioneers who invented early machines like
generator. There are following stages of
evolution of Generators.
 Electrostatic generators.
 Principle of electromagnetic induction.
 Invention of Dynamos.
 Alternators and their evolution.

Electrostatic Generators:
 Before the connection
between electricity and
magnetism was
discovered Electrostatic
generators were
invented.
 They were never used
for commercial power
generation and were
left due to inefficiency
and difficulty.

Principle of electromagnetic
induction:
 The scientific principle
on which modern
generators work was
discovered by Michel
Faraday, he gave first
electrical demonstration
of electromagnetic
induction in august
1831.
 Then he created
world’s first electrical
generator caller
“Faraday’s disk”

Dynamos:
 Dynamos use
electromagnetic
principles to convert
mechanical rotation into
a pulsating direct
electric current through
use of a commutator.
 1st
dynamo was built by
Hippolyte pixii in 1832.

Alternators:
 After that alternating
current generators were
invented. 1st
TWO PHASE
AC GENERATOR was
built by J.E.H.Gordon in
1882.
 In 1886 1st
public
demonstration of
ALTERNATOR SYSEM
was given.
 Lord Kelvin and
Sebastian Ferranti also
done some work.
 Nikola Tesla done very
useful work in evolution of
alternators.

4.Types of Generators:
 According to output generators are of two yes AC
generators and DC generators.
 According to mechanical work input generators can also
be classified. As engine generators , human powered
generators , turbine generators and wind mill generators.

Electromagnetism
 The current magnetizes the iron core and
creates a pair of magnetic poles, one North,
and the other South.
 The two compass needles consequently
point in opposite directions.

Induction
 The light bulb flashes the moment you
connect the switch to the battery.
 The explanation is, that the magnetic
field coming from the upper
electromagnet flows through the lower
iron core.
 The change in that magnetic field, in
turn induces an electric current in the
lower coil.
 The current in the lower coil ceases
once the magnetic field has stabilized.
 If you switch off the current , you get
another flash, because the magnetic
field disappears. The change in the
field induces another current in the
lower core, and makes the light bulb
flash again.

Simple AC Generator
 In this type of generator, a DC source is
supplied to the rotating field coils.
 This produces a magnetic field around the
rotating element.
 As the rotor is turned by the prime mover, the
magnetic field will cut the conductors of the
stationary armature, and an EMF will be
induced into the armature windings.

Alternating Current
 With an alternating current in the electrical grid,
the current changes direction very rapidly, as
illustrated on the graph above.
 Ordinary household current in most of the world
is 230 Volts alternating current with 50 cycles
per second = 50 Hz
 "Hertz" named after the German Physicist H.R. Hertz
(1857-1894).
 The number of cycles per second is also called
the frequency of the grid.
 In USA household current is 130 volts with 60
cycles per second (60 Hz).

Phase Angle
 Since the voltage in an alternating current system keeps oscillating
up and down one cannot connect a generator safely to the grid,
unless the current from the generator oscillates with exactly the
same frequency, and is exactly "in step" with the grid,
 i.e. that the timing of the voltage cycles from the generator coincides
exactly with those of the grid.
 Being "in step" with the grid is normally called being in phase with the
grid.
 If the currents are not in phase, there will be a huge power surge
which will result in huge sparks, and ultimately damage to the circuit
breaker (the switch), and/or the generator.
 In other words, connecting two live AC lines is a bit like jumping onto
a moving seesaw.
 If you do not have exactly the same speed and direction as the seesaw,
both you and the people on the seesaw are likely to get hurt.

Stationary Armature 3 Phase
Generator
Compmotr.gif

Three-Phase AC Generators
 The principles of a three-phase generator are
basically the same as that of a single-phase
generator.
 There are three equally-spaced windings and
three output voltages.
 These are all 120° out of phase with one
another.

Connecting a 3 Phase
Generator to the Network

Phase Angle
 Since the voltage in an alternating current system keeps oscillating
up and down you cannot connect a generator safely to the grid,
unless the current from the generator oscillates with exactly the
same frequency, and is exactly "in step" with the grid,
 i.e. that the timing of the voltage cycles from the generator coincides
exactly with those of the grid. Being "in step" with the grid is normally
called being in phase with the grid.
 If the currents are not in phase, there will be a huge power surge
which will result in huge sparks, and ultimately damage to the circuit
breaker (the switch), and/or the generator.
 In other words, connecting two live AC lines is a bit like jumping onto
a moving seesaw.
 If you do not have exactly the same speed and direction as the seesaw,
both you and the people on the seesaw are likely to get hurt.

Power Quality
 The term "power quality" refers to the voltage
stability, frequency stability, and the absence
of various forms of electrical noise (e.g.
flicker or harmonic distortion) on the electrical
grid.
 More broadly speaking, power companies
(and their customers) prefer an alternating
current with a nice sinusoidal shape.

Starting and Stopping
 Most electronic wind turbine controllers are programmed
to let the turbine run idle without grid connection at low
wind speeds.
 If it were connected to the grid at low wind speeds,
energy will flow from the grid to the turbine and it would
run as a motor.
 The motor may over-speed and be damaged.
 There are several safety devices, including fail-safe brakes, in
case the correct start procedure fails.
 Once the wind becomes powerful enough to turn the
rotor and generator at their rated speed, the turbine
generator becomes connected to the electrical grid at the
right moment.
 This is done using electrical controllers.

Effects of Sudden Starts
 If you switched a large wind turbine on to the
grid with a normal switch, the neighbors would
initially see a brownout
 This is because of the current required to magnetize
the generator.
 This is followed by a power peak due to the
generator current surging into the grid.
 Another unpleasant side effect of using a "hard"
switch would be to put a lot of extra wear on the
gearbox, since the cut-in of the generator would
work as if you all of a sudden slammed on the
mechanical brake of the turbine.

Soft Starting with Thyristors
 To prevent this situation, modern wind turbines are soft
starting.
 They connect and disconnect gradually to the grid using
thyristors, a type of semiconductor continuous switches
which may be controlled electronically.
 You may in fact have a thyristor in your own home, if you own a
modern light dimmer, where you can adjust the voltage on your
lamps continuously.
 Thyristors waste about 1 to 2 per cent of the energy
running through them.
 Modern wind turbines are therefore normally equipped
with a so called bypass switch, i.e. a mechanical switch
 This is activated after the turbine has been soft started,
and the thyristor is bypassed.

Power Quality issues:
Weak Grids
 If a turbine is connected to a weak electrical grid, (i.e. it
is vary far away in a remote corner of the electrical grid
with a low power-carrying ability), there may be some
brownout / power surge problems of the sort mentioned
above.
 In such cases it may be necessary to reinforce the grid,
in order to carry the fluctuating current from the wind
turbine.
 Local power companies have experience in dealing with
these potential problems, because they are the exact
mirror-image of connecting a large electricity user, (e.g.
a factory with large electrical motors) to the grid.

Power Quality Issues: Flicker
 Flicker is an engineering expression for short
lived voltage variations in the electrical grid
which may cause light bulbs to flicker.
 This phenomenon may be occur if a wind turbine
is connected to a weak grid, since short-lived
wind variations will cause variations in power
output.
 There are various ways of dealing with this issue
in the design of the turbine:
 mechanically, electrically, and using power electronics

Power Quality issues:
Islanding
 Islanding is a situation which may occur if a section of the electrical grid
becomes disconnected from the main electrical grid, e.g. because of
accidental or intended tripping of a large circuit breaker in the grid (e.g. due
to lightning strikes or short circuits in the grid).
 If wind turbines keep on running in the isolated part of the grid, then it is
very likely that the two separate grids will not be in phase after a short while.
 Once the connection to the main grid is re-established it may cause huge
current surges in the grid and the wind turbine generator.
 It would also cause a large release of energy in the mechanical drive train
(i.e. the shafts, the gear box and the rotor of the wind turbine) much like
"hard switching" the turbine generator onto the grid would do.
 The electronic controller of the wind turbine will therefore constantly have to
monitor the voltage and frequency of the alternating current in the grid.
 In case the voltage or frequency of the local grid drift outside certain limits
within a fraction of a second, the turbine will automatically disconnect from
the grid, and stop itself immediately afterwards.
 Normally by activating the aerodynamic brakes

D.C. GENERATORS-
CONSTRUCTION & OPERATION
 DC Generators
 Principle of operation
 Action of Commutator
 Constructional details of DC Machine
 Types of DC generators
 EMF Equation

D.C. GENERATORS PRINCIPLE OF
OPERATION
DC generator converts mechanical energy into
electrical energy. when a conductor move in a magnetic
field in such a way conductors cuts across a magnetic
flux of lines and e.m.f. produces in a generator and it is
defined by faradays law of electromagnetic induction
e.m.f. causes current to flow if the conductor circuit is
closed.

Faradays laws
First Law :
Whenever the magnetic flux linked with a circuit changes, an e.m.f. is
always induced in it.
or
Whenever a conductor cuts magnetic flux, an e.m.f. is induced in that
conductor.
Second Law :
The magnitude of the induced e.m.f. is equal to the rate of change of flux
linkages.

Faradays Law of Electromagnetic
Induction
A changing magnetic flux through a loop or loops of wire induces an electromotive
force (voltage) in each loop..

Lenz’s Law
“The induced currents in a conductor are in such a direction as
to oppose the change in magnetic field that produces them..”
“The direction of induced E.M.F in a coil (conductor)
is such that it opposes the cause of producing it..”

Fleming's Right Hand Rule
• The Thumb represents the direction of Motion
of the conductor.
• The First finger (four finger) represents Field.
• The Second finger (Middle finger) represents
Current

Are the basic requirements to be
satisfied for generation of E.M.F
1.A uniform Magnetic field
2.A System of conductors
3.Relative motion between the magnetic
field and conductors

Simple loop generator
with slip ring

Generators
Basic operation of the generatorBasic operation of the generator
As the loop rotates, the magnetic fluxAs the loop rotates, the magnetic flux
through it changes with timethrough it changes with time
This induces an e.m.f and a current in theThis induces an e.m.f and a current in the
external circuitexternal circuit
The ends of the loop are connected to slipThe ends of the loop are connected to slip
rings that rotate with the looprings that rotate with the loop
Connections to the external circuit are madeConnections to the external circuit are made
by stationary brushes in contact with the slipby stationary brushes in contact with the slip
ringsrings

Simple loop generator with split ring

Working Principle of D.C
Generator
Schematic diagram of a simple
DC Generator
1st half cycle(00
to 1800
) Path of current
ABR1B1MLR2B2CD
2st half cycle(1800
to 3600
) Path of current
DCR2B1MLB2R1BA

1)Yoke
- Acts as frame of the machine- Acts as frame of the machine
- Mechanical support- Mechanical support
- low reluctance for magnetic flux- low reluctance for magnetic flux
- High Permeability- High Permeability
- For Small machines -- Cast iron—low cost- For Small machines -- Cast iron—low cost
- For Large Machines -- Cast Steel (Rolledsteel)- For Large Machines -- Cast Steel (Rolledsteel)
Large DC machine
Small DC machine

Constructional Details Of DC Machine
Yoke:
Rotor:
Stator:
Field electromagnets:
Pole core and pole shoe:
Brushes:
Shaft:
Armature:
Coil:
Commutator:
Bearings:

Construction details of DC
generator
Cross section view of dc machine

2)pole cores and pole shoes
a) Pole core (Pole body) :- --Carry the field coilsa) Pole core (Pole body) :- --Carry the field coils
--Rectangle Cross sections--Rectangle Cross sections
-- Laminated to reduce heat losses-- Laminated to reduce heat losses
--Fitted to yoke through bolts--Fitted to yoke through bolts
b) Pole shoe:- Acts as support to field polesb) Pole shoe:- Acts as support to field poles
and spreads out fluxand spreads out flux
Pole core & Pole shoe are laminated of annealed steelPole core & Pole shoe are laminated of annealed steel
(Of thickness of 1mm to 0.25 mm)(Of thickness of 1mm to 0.25 mm)

4)commutator
:--Hard drawn copper bars segments insulated from each:--Hard drawn copper bars segments insulated from each
other by mica segments (insulation)other by mica segments (insulation)
-- Between armature & External circuit-- Between armature & External circuit
-- Split-Rings (acts like Rectifier AC to DC )-- Split-Rings (acts like Rectifier AC to DC )

5&6 Bearings and Brushes
5)Brushes and brush gear:-5)Brushes and brush gear:-
Carbon, Carbon graphite, copper used to Collects currentCarbon, Carbon graphite, copper used to Collects current
from commutation (in case of Generator)from commutation (in case of Generator)
6)Shaft and bearings:-6)Shaft and bearings:-
Shaft-- Mechanical link between prime over and armatureShaft-- Mechanical link between prime over and armature
Bearings– For free rotationBearings– For free rotation

Armature Winding
Armature Winding is classified into two types:
Lap winding
Wave windings

Lap Winding:
 are used in machines designed for low voltage and high current
armatures are constructed with large wire because of high current
Eg: - are used is in the starter motor of almost all automobiles
The windings of a lap wound armature are connected in parallel. This
permits the current capacity of each winding to be added and provides a
higher operating current.
No of parallel path, A=P ; P = no. of poles

Wave winding:
 are used in machines designed for high voltage and low current
 their windings connected in series
 When the windings are connected in series, the voltage of each
winding adds, but the current capacity remains the same
 are used is in the small generator.
 No of parallel path, A=2,

Commutation process in D.C
Generator
 Commutation is the positioning of the DC generator brushes so that
the commutator segments change brushes at the same time the
armature current changes direction.

The total losses in a dc
machine
1.Cu losses
2.Iron losses
3.Mechanical losses
Cupper losses are mainly due to the current passing
through the winding.
1.Armature cu losses (30 to 40% of full load losses)
Cu losses 2.Shunt field cu losses(20 to30% of full load losses)
3.Series field cu losses

1.Cu losses
Armature cu losse s= Ia
2
Ra
Ra=Armature resistance , Ia= Armature current
--Losses due to brush contact resistance is usually include in
armature cu losses
Shunt field cu losses = Ish
2
Rsh
Rsh=Shunt field resistance, Ish=Shunt field
current
Series field cu losses = Ise
2
Rse
Rse=Series field resistance , Ise=Series field
current

2.Iron
losses (Magnetic losses) (20 to 30% of full load losses)
1)Hysteresis losses
2)Eddy current losses

1)Hysteresis losses (Wh)
The losses is due to the reversal of magnetisation of the armature core
Every portion of the rating core passes under N and S poles alternately. There by attaining S
and N polarity respectively. The core undergoes one complete cycle of magnetic reversal after
passing under one pair of poles.
P=No. of poles
N= Armature speed in rpm
frequency of magnetic reversals
f=NP
120
The losses depends upon the volume and B max and frequency of reversals.
Hysteresis losses is given by steinmetz formula
Wh=η B1.6
maxf V wats
V=Volume of the core in m3
η= Steinmetz hysteresis coefficient

2)Eddy current losses:-(We)
when the armature core rotates, it cuts the magenetic flux hence an e.m.f
induced in in the body of the core according to faradays law of electro
magnetic induction. This e. m.f through small sets up large current in the
body of the core due to its mall resistance. This current is known as “Eddy
Current”
We=k B2
maxf2
t2
v2
watts
Bmax=maximum flux densities
f=Freequency of the magenetic
reversals
v=volume of the armaturecore
t=Thick ness of lamination

Efficiency of D.C Generator
Efficiency of generator is defined as the ratio of output power to input power
Efficiency (η) =output ×100
input
input=output+ losses (or) output=input-losses
For D.C generator input mechanical & output electrical

Types of Generators:
 Mainly used generators are engine generators.
They are also known as Gensets. They use
engine, which provides mechanical energy by
use of chemical energy provided by different
chemicals as Gasoline, Propane, Diesel fuel and
Natural gas.
 They can further be classified into 3 main types.
 1.Standby Generators
 2.Portable Generators
 3.Commertial Generators

Standby Generators:
 These are large, often
permanent units often
stationed outside a
building and like to
provide backup power
in case the in electricity
switches off.
 They can sense when a
power interruption has
occurred and
automatically start to
provide emergency
power

Portable Generators:
 These generators are
designed to be
transported whether on
cart trailer or by hand
where there is no utility
of power.
 They are capable of
providing up to 1000
kilowatts of power.
They use either diesel
natural gas , gasoline
or propane as fuel

Commercial Generators:
 In areas where power
supply is intermittent or
lacking as in THIRD
WORLD provincial
areas, generators can
also be set up to
provide additional
power.

Practical Generator
 The actual construction and operation of a practical dc generator
differs somewhat from our elementary generators. The differences
are in the construction of the armature, the manner in which the
armature is wound, and the method of developing the main field. A
generator that has only one or two armature loops has high ripple
voltage. This results in too little current to be of any practical use. To
increase the amount of current output, a number of loops of wire
aroused. These additional loops do away with most of the ripple.
The loops of wire, called windings, are evenly spaced around
the armature so that the distance between each winding is the
same. The commutator in a practical generator is also different. It
has several segments instead of two or four, as in our elementary
generators. The number of segments must equal the number
of armature coils.

Generator hyder

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