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MAGNETIC CIRCUITS - a review -
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Ampere’s law Line integral of magnetic field intensity H around a closed path is equal to the total current enclosed by the path i r H r
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B-H Relation B exists whenever there is H
The strength of B depends on the permeability of the medium Wb/m2 or T o = permeability of free space (4 10-7 H/m) r = relative permeability of medium 1 for air Several hundreds to thousands for ferromagnetic materials
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Magnetic equivalent circuit
N turns l r i
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Magnetic equivalent circuit
N turns r l = F A = magnetomotive force i Magnetic flux density inside the core, The flux crossing the cross section area A of the core, Wb
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Magnetic equivalent circuit
Magnetomotive force Reluctance F R
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Magnetic equivalent circuit
lc Rc Rg lg N i if Rg>> Rc
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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 if Rg>> Rc
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Magnetic equivalent circuit
a’ /2 -/2 - Ni / 2 -Ni / 2
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