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Design of Magnetic Component 3/7/200

By zen

Design of Magnetic Component;by : Ir. ZEN, MT 1

BASIC MAGNETICSBASIC MAGNETICS

THEORYTHEORY

Edited by : Ir. Moh. Zaenal Efendi, MTDepartment Of Electro-industrial Engineering

EEPIS - ITS


BASIC MAGNETICS THEORY

by : ZENTHE ALLIEN GENERATION

REFERENCES :

http://hyperphysics.phy-astr.gsu.edu

Fundamentals of Power Electronics

www.electronics-tutorials.com

INTERNATIONAL RECTIFIER (IRF)

www.electronics-tutorials.com

www.radioelectronicschool.com


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Basic Relationship of Magnetics



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MMF (Magneto Motive Force)

The quantity of magnetic field force, or "push."


MMF can be thought of as the magneticequivalent of electromotive force. You can

calculate it as -

The units of MMF are often stated asampere turns (A-t).

= H le (ampere turns)

= I N (ampere turns)


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Magnetic Flux ()The quantity of total field effect, or "substance" of the field.

Analogous to electric current. (Weber (Wb) or Volt Second)

Magnetic flux is the product of the average magnetic field times the

perpendicular area that it penetrates. It is a quantity of convenience

in the statement of Faraday's Law and in the discussion of objects

like transformers and solenoids. In the case of an electric generator

where the magnetic field penetrates a rotating coil, the area used in

defining the flux is the projection of the coil area onto the plane

perpendicular to the magnetic field.


Flux Density (B)(Webers per metre2 ---- Wb/m2 or Tesla)

Flux density is simply the total flux divided by the

cross sectional area of the part through which it

flows:

B = / Ae tesla

Flux density is related to field strength viathepermeability:

B = H


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Effective length ( le ) metre

The 'effective length' of a core

is a measure of the distance

which flux lines travel in

making a complete circuit of it

In the toroid example the path length could be determined

approximately as :

le = (dl + dm) / 2

le = (12.7 + 6.3) / 2 = 29.8 mm

dl

dm


Cross Sectional Area

Effective Area [ ])metresquare()AorA(

2ec

m

The 'effective area' of a core

represents the cross sectional

area of one of its limbs.

Usually this corresponds

closely to the physical

dimensions of the core


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Cross Sectional Area of Toroid Core

or

Ae = hln2(R2/R1) / (1/R1-1/R2) m

2

Ae = h ((dl - dm) / 2)

= 6.3

((12.7 - 6.3) / 2) = 20.2 mm2

dm

dl



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Permeability ()(henrys per metre h/m) -----= L/d

The specific measure of a material's acceptance of magnetic flux,analogous to the specific resistance of a conductive material () inelectric circuit.

Just as those materials with high electrical conductivity let electriccurrent through easily, so materials with high permeabilities allowmagnetic flux through more easily than others.

Materials with high permeabilities include iron and the otherferromagnetic materials. Most plastics, wood, non ferrous metals, airand other fluids have permeabilities very much lower: 0.

The magnetic permeability, , of a particular material is defined as

the ratio of flux density to magnetic field strength - = B/H


Electric and Magnetic Constants

The electric permittivity of free space

The magnetic permeability of free

space is taken to have the exact value


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Km or r: a relative permeability.

00m ;k ror ==

Permeability of materials is.

Approximate maximum permeabilities


Magnetic Field Strength (H)(Field Intensity)

(ampere per metre --- A/m)

The amount of field force (mmf) distributed over the length of the

electromagnet. Sometimes referred to as Magnetizing Force.

The magnetic fields generated by currents and are characterized by the

magnetic field B measured in Tesla.

It has been common practice to define another magnetic field quantity, usually

called the "magnetic field strength" designated by H. It can be defined by the

relationship

where

If the material does not respond to the external magnetic field by producing any

magnetization, then Km = 1.

HBB

H

== ;

0= mK


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Reluctance ( ) or Rm

(perhenry (H-1) or ampere-turns per weber )

The opposition to magnetic field flux through a

given volume of space or material. Analogous to

electrical resistance.

Reluctance is the ratio of mmf to flux :

A

le

AeB

leH

=

=

= H

B

where =:



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EMF (Electromotive Force)

The magnetic force exerted on the charges in a moving

conductor will generate a voltage (a motional emf). This motional

emf is one of many settings in which the generated emf is

described by Faraday's Law.


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FARADAYS LAW



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The motional emf expression is an application of Faraday's Law, as can

be seen from:

EMF and Faraday's Law


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Lenz's Law

When an emf is generated by a change in magnetic flux according to Faraday's

Law, the polarity of the induced emf is such that it produces a current whosemagnetic field opposes the change which produces it. The induced magnetic

field inside any loop of wire always acts to keep the magnetic flux in the loop

constant. In the examples below, if the B field is increasing, the induced field

acts in opposition to it. If it is decreasing, the induced field acts in the direction

of the applied field to try to keep it constant.


AMPERES LAW

----- (N I) Ampere Turns


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----- (N I) Ampere Turns


Current density (J)

(Amperes per square A/m2)

Current density is simply the total electric

current divided by the area over which it is

flowing.

Generally J is about 1.5 to 5 amps per

square millimetre. A good starting point is3.5 A/mm2)


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Analogy with electric quantities

resistancereluctance

current densitymagnetic flux density

currentmagnetic flux

conductivitypermeability

electric field strengthmagnetic field strength

electromotive force (voltage)magnetomotive force

Electric QuantityMagnetic Quantity

Electric analogues


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Home work ( one week ):

1.Whats some benefit of understanding of

Magnetics

2.Whats differences of MMF and EMF

3.Explain about process of EMF generation

4.Explain about magnetic circuit and

compare with electric circuit

5.Re-write this hand-out in Indonesia !!!

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