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# Re: [femm] Re: BH data

- To: femm@yahoogroups.com
- Subject: Re: [femm] Re: BH data
- From: Keith Gregory <k.gregory@lboro.ac.uk>
- Date: Mon, 28 Oct 2002 08:53:27 +0000
- In-reply-to: <20021025235742.7910.qmail@web10004.mail.yahoo.com>
- References: <5.1.0.14.0.20021025082557.01d63008@staff-mailin.lboro.ac.uk>

`I'm not sure that you can "differentiate" because eddy-currents are part of what constitutes the apparent inductance of a system. Eddy-currents always oppose the driving current (Lenz's law) and tend to reduce flux, this appears externally as a reduction in self-inductance. In transformers and electrical machines operating at 50Hz I have usually found that static analysis gives a pretty good assessment of field distribution and allows inductances to be determined within 10% or so. This is particularly so in saturated conditions where an ac analysis may not be possible. However, this depends quite significantly on the construction of the problem. It most certainly would not be the case in un-laminated situations, where core eddy-currents usually have dramatic effects. The effects of non-uniform current distribution in conductors and windings is also not considered. It really is a typical design problem - deciding what can and can't be neglected in a particular situation. For example, MikeH says "A basic model LVDT model using mumetal core at even 100 Hz shows pronounced skin effect.". I was surprised by this but find it perfectly believable. It would be interesting to see how the measured inductances of such an LVDT compare to calculation.`
`Sorry - I've been rambling a bit and probably have not answered your question.`
`Keith.`
`
At 16:57 25/10/2002 -0700, you wrote:`

> `I am just wondering how do you differentiate the effect of self inductance vs. eddy current in FEMM? At 10 - 100Hz, I would think that the self inductance is the one to consider.`
> ``

>     Keith Gregory <k.gregory@lboro.ac.uk> wrote:
>     At 15:31 24/10/2002 +0000, you wrote:
>     >--- In femm@y..., Keith Gregory <k.gregory@l...> wrote:
>     > > Mike,
>     > >
>     > > I think you would find that static finite elements models with
>     >single
>     > > valued magnetization characteristics would give pretty good
>     >approximations
>     > > of field distribution and winding inductances in the 50-60Hz types
>     >of
>     > > applications where the materials are laminated. Although
>     >calculating
>     > > inductances in saturated conditions is complicated. Loss
>     >calculations even
>     > > at 50 or 60 Hz are not as straightforward. Operating in Khz I
>     >really have
>     > > no idea how good results would be.
>     >
>     >
>     >A basic model LVDT model using mumetal core at even 100 Hz shows
>     >pronouned skin effect. At 5kHz there is a danger of saturation near
>     >the material surface at normal drive levels.

>     The 5kHz doesn't surprise me but the 100Hz does, although mumetal is
>     different to the materials I would normally work with.

>     > >
>     > > >I am currently interested in trying to observe Barkhausen noise for
>     > > >NiFe materials. I expect to use up to about 100 Hz field for this,
>     >and
>     > > >believe that the spectrum of the noise will contain much
>     >information,
>     > > >if it can be unravelled; early days yet. Comments are very welcome
>     > >
>     > > The classic demonstration of Barkhausen jumps is done with "DC"
>     > > magnetization, usually with a permanent magnet. I have a vague
>     >memory of a
>     > > paper describing a different way which can produce noise displays
>     >on an
>     > > oscilloscope. I'm not sure what information it would contain
>     >though, what
>     > > had you got in mind?
>     >
>     >
>     >I hope to use LF ac to cycle the jumps and give larger noise output.
>     >Literature suggests that Barkhausen noise can indicate heat treatment
>     >and internal stresses, inter alia; as properties of cores are
>     >affected by handling stresses I believe BN can provide an insightful
>     >tool into known quality issues.

>     I could see that, since Barkhausen noise has been attributed to sudden
>     domain wall movement and some people say that it is impurities and voids in
>     the material that make the walls stick, the amount of noise could give an
>     indication of the material structure and quality.

>     It would be interesting to see if it really is "noise" or it has some
>     pattern during repeated cycles.

> `> > In addition, if my memory serves aren't there several different
> >Radiomental
> > > alloys differentiated by a number such as Radiometal 36?
> >
> >
> >Yes. The 36 refers to % nickel in the alloy. Varoius types give
> >different permeability / resistivity / cost materials for different
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    <html>
    I'm not sure that you can &quot;differentiate&quot; because eddy-currents
    are part of what constitutes the apparent inductance of a system.
    Eddy-currents always oppose the driving current (Lenz's law) and tend to
    reduce flux, this appears externally as a reduction in self-inductance.
    In transformers and electrical machines operating at 50Hz I have usually
    found that static analysis gives a pretty good assessment of field
    distribution and allows inductances to be determined within 10% or so.
    This is particularly so in saturated conditions where an ac analysis may
    not be possible. However, this depends quite significantly on the
    construction of the problem. It most certainly would not be the case in
    un-laminated situations, where core eddy-currents usually have dramatic
    effects. The effects of non-uniform current distribution in conductors
    and windings is also not considered. It really is a typical design
    problem - deciding what can and can't be neglected in a particular
    situation. For example, MikeH says &quot;A basic model LVDT model using
    mumetal core at even 100 Hz shows pronounced skin effect.&quot;. I was
    surprised by this but find it perfectly believable. It would be
    interesting to see how the measured inductances of such an LVDT compare
    to calculation.<br><br>
    Sorry - I've been rambling a bit and probably have not answered your
    question.<br><br>
    Keith. &nbsp; <br><br>
    <br>
    At 16:57 25/10/2002 -0700, you wrote:<br><br>
    <blockquote type=3Dcite class=3Dcite cite>I am just wondering how do you
    differentiate the effect of self inductance vs. eddy current in
    FEMM?&nbsp; At 10 - 100Hz, I would think that the self inductance is the
    one to consider. <br><br>
    &nbsp; <br><br>
    &nbsp;<b><i>Keith Gregory &lt;k.gregory@lboro.ac.uk&gt;</i></b> wrote:=20
    <dl><tt>
    <dd>At 15:31 24/10/2002 +0000, you wrote:
    <dd>&gt;--- In femm@y..., Keith Gregory &lt;k.gregory@l...&gt; wrote:
    <dd>&gt; &gt; Mike,
    <dd>&gt; &gt;
    <dd>&gt; &gt; I think you would find that static finite elements models
    with
    <dd>&gt;single
    <dd>&gt; &gt; valued magnetization characteristics would give pretty
    good
    <dd>&gt;approximations
    <dd>&gt; &gt; of field distribution and winding inductances in the
    50-60Hz types
    <dd>&gt;of
    <dd>&gt; &gt; applications where the materials are laminated. Although
    <dd>&gt;calculating
    <dd>&gt; &gt; inductances in saturated conditions is complicated. Loss
    <dd>&gt;calculations even
    <dd>&gt; &gt; at 50 or 60 Hz are not as straightforward. Operating in Khz
    I
    <dd>&gt;really have
    <dd>&gt; &gt; no idea how good results would be.
    <dd>&gt;
    <dd>&gt;
    <dd>&gt;A basic model LVDT model using mumetal core at even 100 Hz=20
    shows
    <dd>&gt;pronouned skin effect. At 5kHz there is a danger of saturation
    near
    <dd>&gt;the material surface at normal drive levels.<br><br>

    <dd>The 5kHz doesn't surprise me but the 100Hz does, although mumetal is=20
    <dd>different to the materials I would normally work with.<br><br>

    <dd>&gt; &gt;
    <dd>&gt; &gt; &gt;I am currently interested in trying to observe
    Barkhausen noise for
    <dd>&gt; &gt; &gt;NiFe materials. I expect to use up to about 100 Hz
    field for this,
    <dd>&gt;and
    <dd>&gt; &gt; &gt;believe that the spectrum of the noise will contain
    much
    <dd>&gt;information,
    <dd>&gt; &gt; &gt;if it can be unravelled; early days yet. Comments are
    very welcome
    <dd>&gt; &gt;
    <dd>&gt; &gt; The classic demonstration of Barkhausen jumps is done with
    &quot;DC&quot;
    <dd>&gt; &gt; magnetization, usually with a permanent magnet. I have a
    vague
    <dd>&gt;memory of a
    <dd>&gt; &gt; paper describing a different way which can produce noise
    displays
    <dd>&gt;on an
    <dd>&gt; &gt; oscilloscope. I'm not sure what information it would
    contain
    <dd>&gt;though, what
    <dd>&gt; &gt; had you got in mind?
    <dd>&gt;
    <dd>&gt;
    <dd>&gt;I hope to use LF ac to cycle the jumps and give larger noise
    output.
    <dd>&gt;Literature suggests that Barkhausen noise can indicate heat
    treatment
    <dd>&gt;and internal stresses, inter alia; as properties of cores are
    <dd>&gt;affected by handling stresses I believe BN can provide an
    insightful
    <dd>&gt;tool into known quality issues.<br><br>

    <dd>I could see that, since Barkhausen noise has been attributed to
    sudden=20
    <dd>domain wall movement and some people say that it is impurities and
    voids in=20
    <dd>the material that make the walls stick, the amount of noise could
    give an=20
    <dd>indication of the material structure and quality.<br><br>

    <dd>It would be interesting to see if it really is &quot;noise&quot; or
    it has some=20
    <dd>pattern during repeated cycles.<br><br>

    <dd>&gt; &gt; In addition, if my memory serves aren't there several
    different
    <dd>&gt;Radiomental
    <dd>&gt; &gt; alloys differentiated by a number such as Radiometal 36?
    <dd>&gt;
    <dd>&gt;
    <dd>&gt;Yes. The 36 refers to % nickel in the alloy. Varoius types give
    <dd>&gt;different permeability / resistivity / cost materials for
    different
    <dd>&gt;applications.&lt;<a href=3D"http://webhosting.yahoo.com/";>Y! Web
    Hosting</a> - Let the expert host your web site
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`</dl></blockquote></html>`
`--=====================_3573268==_.ALT--`

- References:
  - Re: [femm] Re: BH data
    - From: Keith Gregory <k.gregory@lboro.ac.uk>
  - Re: [femm] Re: BH data
    - From: Muchlis Achmad <machmad@yahoo.com>

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