MAGNETIC CIRCUITS - a review -

1. MAGNETIC CIRCUITS - a review -

2. 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

3. 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

4. l r Magnetic equivalent circuit N turns i

5. 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

6.  Magnetomotive force Reluctance  F R Magnetic equivalent circuit

7. lc Rc i lg N Rg if Rg>> Rc Magnetic equivalent circuit

8. 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

9.  Ni / 2  - /2  -/2 -Ni / 2 Magnetic equivalent circuit a a’