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# Re: [femm] Eddy currents in thick laminations

- To: femm@yahoogroups.com
- Subject: Re: [femm] Eddy currents in thick laminations
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Tue, 23 Oct 2001 12:02:06 -0400
- Organization: Foster-Miller, Inc.
- References: <9r3p0h+d81r@eGroups.com>

    Douglas@magtech.co.uk wrote:

    > Problem:
    >
    > How does one approach determining the eddy-current losses in
    > a "laminated material" with a thickness of several millimeters and
    > where the frequency under consideration is greatly above the more
    > usual 50-60Hz range. Surely the skin depth must now become an issue,
    > as the lamination is no longer a "thin" conductor with uniform
    > current density. The simpler (freshman textbook type) formulas no
    > longer apply? Any pearls of wisdom would be most appreciated.
    >
    > Douglas Stevenson

    Also, I forgot to say that the formulation that femm uses to treat
    laminations is the one from Stoll that includes skin effects. In his book,
    he develops an apparent, frequency-dependent permeability that includes the
    skin effects. When you calculate the "Hysteresis and/or Laminated Eddy
    Current Losses" integral or the "Total Losses" integral, the losses are
    calculated in a way that includes the skin effects. There is some info about
    this in Appendix B of the manual.

    Some things to be careful of however--the laminated eddy current formulation
    doesn't consider nonlinear material properties. If you have a thin skin
    region, it's pretty easy to make that region highly saturated. If this is
    the case, the model (which assumes linear material properties) is less
    accurate. Also, if the material properties (permeability, conductivity, and
    "hysteresis lag" parameter) aren't carefully chosen (perhaps on the basis of
    experiments with test rings of your material), the loss predictions can be
    not very accurate.

    Dave.

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- References:
  - Eddy currents in thick laminations
    - From: Douglas@magtech.co.uk

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