Ch 1 emachines cdr Ong

8/14/2019 Ch 1 emachines cdr Ong

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ELECTRICAL MACHINE

EEP 3243

Lt Cdr Ong Khye Liat RMN


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INTRODUCTION


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Electrical Machine Introduction

An electric machine is a device whicho nver ts el ectri cal p oweronv erts el ectri cal p ower( )voltages and currents intoe chan ical powerech anic al power (torque and),rotational speed r vic e ve rsar vi ce ve rsa

and han ges AC v olt agehan ges AC vol tage from one.

level to another level


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Cont.

Electrical machines are divided into:three categories

Generator

Motor Transformer


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Cont.

A generator is a dynamic electricalenergy machine thatconverts mechanical energy at

its prime mover to produce

electrical energy .at its output Generator is classified into two: .

types AC generator and DC generator


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Cont.

Motor is the device thatconverts electrical energy at its

input to produce mechanical energy.

:Motor is classified into two types AC.motor and DC motor


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Transformer is the device thatconverts AC voltage from one level

to another level higher or lower, or

even to the same level withoutchanging the frequency.


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The capability of a machineperforming as one or the other is

often through the action of a

,magnetic field to perform such.conversions


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FUNDAMENTALS OF

ELECTRICITY, MAGNETISM,AND CIRCUITS


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Fundamentals of Electricity

Electricity ,a form of energy produced in

,various ways which provides power to

, ,devices that create light heat.movement etc


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Current The rate of change of charge is

. / .called current SI unit C s or Ampere

Current Charge Flow Vs ConventionalCharge Flow


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Fundamentals of Magnetism

The magnet is the property of a materialwhich can attract or repel of other iron

.material

Magnetism is the amount of force that.creates by electric current Electromagnet is one kind of temporary

magnet that produced by electric current

.flowing through a conductor


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Around the magnet where the force.acts is called magnetic field The

intensity of the magnetic field is

more near the poles and it decreases.slowly away from the pole


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The amount of magnetic field linespassing through the area near the

,magnet is called the magnetic flux

. and in unit Wb ,Magnetic flux density B is defined asthe ratio of magnetic flux per unit.area Its unit is Tesla or Wb per

.square meter


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The magnetomotive force ( ),MMF Fis definedas the product of current and the number

.of turns of the coil

F=NI At Magnetic field intensity is defined as the

.magnetomotive force per unit length


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The permeability of the material offers.conductivity for the flux

High conductivity offers high permeability

.and vice versa Relative permeability is the ratio of

(permeability of any medium ) to the(permeability of the free space o)*1

:Note o =4x 10-7 /H m


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The magnetic flux density ( )B createdin a magnetic material is directly

proportional to the amount of

applied magnetic field intensity ( )H. =B roH


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(Reluctance R) is the property ofmagnetic material to oppose the

.creation of magnetic flux

It also defined as the ratio ofmagnetomotive force to the flux

through any cross section of.magnetic circuit


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,Mathematically R ,can be expressed as


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Permeance (P)is defined as the ratioof magnetic flux to the

magnetomotive force through any

cross section of the magnetic.circuit

,Mathematically P is the reciprocal

.of reluctance


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Fundamentals of Circuit

The magnetic circuit is the closed.path followed by the magnetic flux

:It is divided into 2 types

Series magnetic circuit Parallel magnetic circuit


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Series MagneticCircuit

Equivalent SeriesCircuit


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Parallel MagneticCircuit

Equivalent ParallelCircuit


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Magnetic Circuitwith Air Gap

Equivalent Circuit


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Magnetic Vs Electric Circuit

(Flux magnetomotive force per) (reluctance Vs current voltage per).resistance

EMF Vs MMF Reluctance Vs Resistance Permeability Vs Conductivity


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Electromagnetic Force

When a current carrying conductor isplaced in a magnetic field it

,experiences a electromagnetic force

.which called Lorentz force

This force has a basic importance for,working principle of motor

, .generator etc


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Cont.

,Lorentz force F F = BlI

,Where B : ( ),magnetic flux density T l : ( ),length of the conductor m I :current flowing through the conductor


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Forces Between 2 ParallelConductors

The total reduction influx indicates theforce of attraction

The net flux isincreased whichindicates the force of

repulsion


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Hysteresis Loop

Hysteresis is a term which is used todescribe systems which have memory; that

,is the effects of the current input to

the system are not felt at the same

.instant


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Hysteresis losses

Each time the magnetic field is,reversed a small amount of energy

is lost due to hysteresis within the

. ,core For a given core material the

loss is proportional to the,frequency and is a function of the

peak flux density to which it is

.subjected


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Loss in Magnetic Field

2 types of losses are considered in.the magnetic field

Hysteresis loss

Eddy current loss Combination of this 2 losses known as

.core loss


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Hysteresis loss

Ph = khVcvolBmn

f

Where,

kh : is a constant depends on the properties of the material and core volume.

Vcvol = lA : is the core volume.n ; varies between 1.5 to 2.5

Bm : Max value of flux density

f : is the frequency


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Eddy Current Loss

Ferromagnetic materials are also,good conductors and a solid core madefrom such a material also constitutes a

-single short circuited turn throughout

.its entire length Eddy currentstherefore circulate within the core in a,plane normal to the flux and are

responsible for resistive heating of the

.core material


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Cont. Pe = keVcvol t

2Bm2f2

Where,

ke : is a proportionality constant depends on the properties of the material and

lamination thickness.

Vcvol = lA : is the core volume.

Bm : Max value of flux density

f : is the frequencyt : thickness of the lamination


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END OF PART 1


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Practice Problem 1 The dimensions of the magnetic circuit shown

. , . . .below 0 2m 0 02m and 0 2m respectively Therelative permeability of a magnetic material

. ,is 750 Calculate the field intensity H.


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Solution

,The value of magnetomotive force is F F = NI = 330 X 0.6A = 198 At


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,Mean length of the path is lc lc = (0.2 0.02) 4 = 0.72 m

,Cross sectional area A A = 0.02 x 0.02 = 0.0004 m2


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,The value of reluctance is R


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,The value of flux


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,Magnetic Flux density B


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,Magnetic field intensity H

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Ch 1 emachines cdr Ong