MAGNETIC CIRCUITS

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MAGNETIC CIRCUITS - a review -
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Amperes law
Line integral of magnetic field intensity H
around a closed path is equal to the total
current enclosed by the path
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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
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Magnetic equivalent circuit
N turns
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Magnetic equivalent circuit
N turns
F
magnetomotive force
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Magnetic equivalent circuit
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Magnetic equivalent circuit
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Magnetic equivalent circuit

• In electrical machine with ferromagnetic
  material, ?c gtgt ?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

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Magnetic equivalent circuit
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