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# inductance calculations in nonlinear material

- To: femm@yahoogroups.com
- Subject: inductance calculations in nonlinear material
- From: corneliuspaul@gmx.de
- Date: Wed, 11 Jul 2001 13:34:03 +0200 (MEST)

    k.gregory@lboro.ac.uk wrote

    >Cornelius,
    >
    >If you get chance try an experiment. From your FEMM model determine the
    >self-inductance of both windings and the mutual inductance between them.
    >Then subtract the mutual from the square-root of the product of the two
    >self-inductances and see how the result compares with your other
    calculations.

    I will certainly do that, it is on my list of things to be done
    to get a feeling of how well the model corresponds to reality and
    common transformer formulas.

    Anyway, as far as I understand it, the direct calculation of mutual
    inductance
    can only be done via the flux linkage approach.
    Flux linkage must be determined from the magnetic vector potential
    difference
    which is an order less accurate than energy computed from variational FEM.

    Therefore I expect some differences in the results per se.

    >It should be possible as well to model the transformer in the section at
    >right angles to the normal one to get some idea of the end-winding leakage.
    >Because the leakage is mostly in air superposition theory should apply
    >reasonably well and you may be able to just add the leakage fluxes
    >together. You need to be aware though that the core material will be at a
    >different level of saturation in the "end-winding" model although you
    >could make the core material linear and set its permeability to a typical
    >value from the "normal" model.
    >
    >Remember as well that with ferromagnetic or ferrimagnetic core materials
    >the inductances will be functions of current because of saturation,
    >although this may not affect the leakage too much.

    As I see it the affect of nonlinear core material on leakage inductance
    can merely be neglected,
    at least at the level of accuracy I need here.

    Computing the proper values for self inductances when nonlinear core
    material
    is present is another chapter though!
    Up to now I have only used linear material,
    I have not yet fully understood how to interpret the different "inductance"
    values that can be computed from energy / coenergy / apparent energy ...

    regards,
    Cornelius

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