MAGNETIC CIRCUITS - a review -

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# MAGNETIC CIRCUITS - a review - - PowerPoint PPT Presentation

MAGNETIC CIRCUITS - a review -. i. H. r. r. Ampere’s law. Line integral of magnetic field intensity H around a closed path is equal to the total current enclosed by the path. Wb/m 2 or T.  1 for air Several hundreds to thousands for ferromagnetic materials. B-H Relation.

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MAGNETIC CIRCUITS

- a review -

i

H

r

r

Ampere’s law

Line integral of magnetic field intensity H around a closed path is equal to the total current enclosed by the path

Wb/m2 or T

 1 for air

Several hundreds to thousands for ferromagnetic materials

B-H Relation

• B exists whenever there is H
• The strength of B depends on the permeability of the medium

o = permeability of free space (4 10-7 H/m)

r = relative permeability of medium

l

r

Magnetic equivalent circuit

N turns

i

l

r

A

Magnetic flux density inside the core,

Wb

The flux crossing the cross section area A of the core,

Magnetic equivalent circuit

N turns

= F

= magnetomotive force

i

Magnetomotive force

Reluctance

F

R

Magnetic equivalent circuit

lc

Rc

i

lg

N

Rg

if Rg>> Rc

Magnetic equivalent circuit

if Rg>> Rc

Magnetic equivalent circuit

• In electrical machine with ferromagnetic material, c >> o
• It is permissible to assume that ALL MMF drop appear across the air gap
• Since magnetic path crosses the airgap twice, half of the MMF appear at each air gap

Ni / 2

-

/2

-/2

-Ni / 2

Magnetic equivalent circuit

a

a’