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# Re: [femm] Femm releases 3.3 - 3.2

- To: femm@yahoogroups.com
- Subject: Re: [femm] Femm releases 3.3 - 3.2
- From: David Meeker <dmeeker@ieee.org>
- Date: Sun, 15 Dec 2002 16:33:42 -0500
- References: <athp60+10d11@eGroups.com>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.1) Gecko/20020826 MultiZilla/v1.1.22

ac090960 wrote:

> `Hello,
> Making some trials with the new release 3.3 (downloaded today) on an
> AC axisymmetric geometry an error occurred during FKN execution: (On-
> edge lamination not supported in AC analyses).
> The strange is the same problem is running using the release 3.2.
> `

The 3.2 version will let you evaluate this problem, but the problem it's solving is not the problem that you probably intended. For on-edge laminations, the total current inside each lamination should add up to zero inside the cross-section of each lamination if you have a tape-wound core, or if you are considering penetrations into a laminated stack. However, this condition isn't enforced in the way that the on-edge problems were implemented in 3.2, so the result that you get is for the analysis of a series of concentric iron rings rather than one long tape in the axi case, or you get the results for a stack of laminations where all the laminations in the stack are shorted together at +/- infinity. This isn't what people are usually intending by doing the on-edge lamination analysis, so I changed the program so that it just doesn't allow the user to run the on-edge model for harmonic problems in the 3.3 version, as well as in the 03Dec02 update of 3.2.
There is, however, no problem with the in-plane laminations (e.g. stacked laminations in a transformer or motor core). In the in-plane case, the eddy currents always integrate to zero across the thickness of the lam (unlike the on-edge case), so it is reasonable to represent the combined eddy current/hysteresis effects via an equivalent bulk material with a zero conductivity and a complex-valued permeability (how femm does the in-plane laminations internally).
If you want to analyze problems with on-edge laminations, (e.g.. tape-wound core or penetration of the flux into a laminated planar stack through the sides of the laminations), you'll need to model the individual laminations and impose a separate circuit condition on each one to force the net current in each lamination to add up to zero (I know this is a drag to do). I've attached an example of a tape-wound core that has been done by modeling each lamination in this way.
Dave.

    --
    David Meeker
    dmeeker@ieee.org
    http://femm.berlios.de/dmeeker

Attachment: `zip00043.zip`
Description: Zip compressed data

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