[SI-LIST] Re: Transformer Hum
- From: steve weir <weirsp@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sun, 18 Apr 2004 16:59:08 -0700
John, that is not quite right. What you describe is the ordinary behavior
of a mag-amp. The mechanical force is proportional to B squared. When the
material saturates, the slope of B/H ( inductance ) drops. So, while I,
and consequently H rise rapidly, B and the mechanical force do not. If you
want to think about this intuitively consider that an electromagnet does
not increase markedly in strength once it saturates, the wires just heat up
rapidly.
Regards,
Steve.
At 01:49 PM 4/18/2004 -0400, John Wilson wrote:
>Another reason, which is only an externsion of what Geog outlined below,
>is that
>the transformer in question might be saturating. If the magnetic material
>saturates (integ(V*dS)) then the peak current (which will occur each time the
>transformer saturates) can be quite large. Take a look at a typical B vs. H
>characteristic for a magnetic material and you will see how high the H-field
>(proportional to current) can become when the material saturates.
>
>The magneto-striction due to the large currents will make a transformer "hum".
>
>Checke the specs. on the transformer an see if you exceeded its limits.
>
>john
>
>Georg Ramsch wrote:
>
> > Hello, Steve !
> >
> > There may be 2-3 reasons for the hum, as far as I know:
> >
> > a) small transformer: the windings may not be wrapped tense enough
> > around the iron core. The magnetic field changes cause the
> > windings to swing, which is audible.
> > b) if the transformer is controlled by a non zero-phase switching
> > device, the current transients may cause the effect from a), even
> > with tense windings.
> > c) larger transformer show magnetostriction, which transfers into
> > audible noise( means: the iron core mechanical dimensions swing
> > with the magnetic field )
> >
> > a) and b) may have a solution,
> > but c) may be tricky. => what about a torroid core ?
> > From my own experience: given a 100 MVA transformer station, you cannot
> > enter without a "mickey mouse" ear protection because of the loud "hum"
> > of magnetostriction of those big ones.
> >
> > My 2 cents
> >
> > Georg
> >
> > Steve GullWing UK schrieb:
> >
> > >Dear SI'ers,
> > > I have some products recently released to
> production and
> > >the Transformers are exhibiting a Hum. Anybody got any idea how to solve
> > >this ?
> > >Regards
> > >Steve
> > >GullWing Ltd
> > >
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Steve Weir
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
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