On Sunday, September 7, 2014 4:51:44 AM UTC-4, Daniel wrote:
> On Saturday, 6 September 2014 11:05:58 UTC+10, Don Kelly wrote:
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> > On 05/09/2014 6:15 AM, Daniel wrote:
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> >
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> > > On Saturday, 1 January 2000 19:00:00 UTC+11, D.H. Kelly wrote:
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> > >> Your concern over this assertion was well placed. It would have been
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> >
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> > >> possible to use integral of H.dl around loop = current enclosed- hence
H and
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> > >> flux outside the core whatever the mu. (which you did as part of your>
development.) You went a step further and I, for one, am glad that you did.
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> > >> Don Kelly
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> > >> dkelly@nabunalimo.lark.com
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> >
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> > >> remove the bull to reply
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> > >>
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> >
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> > >> BillyFish wrote in message
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> > >> news:20000101001804.15555.00000237@ng-ce1.aol.com...
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> > >
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> > >>> Let me point out that this whole thread started because someone made
the
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> > >>> assertion that increasing the mu of the core to very high values would
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> > >> prevent
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> > >>> any flux outside the core. I think that the consensus now is that
such an
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> >
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> > >>> assertion is erroneous. This glib assertion suckered me in. In a
sense,
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> >
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> > >> it
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> >
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> > >>> was a scam artist at work. Well meaning maybe, but a scam artist
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> >
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> > >> nevertheless.
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> > >>> I just had to *understand* why it was erroneous. The scam misses the
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> >
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> > >> point
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> > >>> that a parallel H and E do not generate a Poynting vector. Once that
is
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> > >>> realized, everything else follows rather easily.
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> > >>>
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> > >>> Bill
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> > >
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> >
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> > > so after 14 years was the conclusion reached that leakage inductance is
in fact essential to transformer power transfer.. or an unfortunate, usually
small but inescapable component which reduces coupling and hence reduces
efficiency?
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> > >
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> > > thx...
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> > >
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> > Diclaimer:- I am not the Don Kelly "quoted" above. I vaguely recall
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> >
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> > someone making statements in my name.
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> > If you removes the "bull" to reply- then you are replying to an empty
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> > message.
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> > Leakage reactance is NOT "essential" to transformer power transfer. It
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> > is a result of the fact of life that two conductors cannot be
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> > superimposed to share the same space. One can come close-particularly
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> > with some toroidal LV transformers-but....
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> > However, efficiency in the normal sense of
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> > (real power out/real power in)
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> > depends on resistance, not leakage reactance.
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> > There is no wonderful conclusion after 14 years- the conclusion came
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> > over 114 years ago. That is that coupling is not perfect-hence leakage
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> >
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> > reactance.
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> >
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> > --
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> >
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> > Don Kelly
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> >
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> > remove the cross to reply
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> Nice to hear from you (DK - the voice of reason) again...
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>
>
> It was just that I seem to remember the idea that leakage L was an essential
component for Tx operation was arrived at after the discussion between Billy
Fish and Electric Pete... and that always urked me. Yes I agree the of course
that the magnetic
field being set up by the stray inductance does not dissipate any (real)
energy so does not reduce the efficiency electrically... Nice to know that
there is nothing that I am missing then...
Tom Tech,
I somewhat stumbled upon this interesting discussion regarding the power
transfer in iron core transformers via leakage flux or core flux. I have given
it MUCH thought and experimentation and research thru many college and
manufacturers text books
regarding transformer theory and construction. Until I took a much deeper look
into the transfer mechanism, I too was convinced thru what I thought was a
common view that energy is transferred via the core from one winding to
another. I do not hold that
view today. Several things can shed light on the somewhat hard to see transfer
mechanism. Yes, alternating flux in the iron core is responsible for the
induced EMF we see in any winding around the core, however when secondary load
current flows (assume a
resistive load), the secondary H field tries to reduce the core flux, and does
for a very brief period, reducing the induced "Back EMF" seen in the primary.
More current flows in the primary to maintain the core flux, however,
regardless of how high the
core permeability is,"leakage Flux" will be produced. The term "leakage flux"
is perhaps a misnomer, as it implies a fault in materials. Under load
conditions, the "Leakage" flux will always be produced. This H "leakage" flux
is in phase with the primary
voltage and in phase with the induced EMF in the secondary winding for "Real
Power". Note that the core flux does not change, at least not much, maybe a
little due to IR drops in the primary winding. If you work out the Poynting
Theorem, it will show the
induced EMF normal to the H flux from primary current to represent real power
flow into the secondary winding. Remember core flux is lagging the primary
voltage 90 degrees or so. Another insight is that under loaded conditions,
there is MUCH MORE energy
in the "Leakage" H flux than in the core flux. The "leakage" flux has a very
high field intensity, that, when crossed with induced EMF is real power flow.
If one examines the signal times thru for instance, an audio interstage
transformer, you will see
the time required to pass thru the transformer is much faster than it would be
if it had passed thru the high permeability iron core region. I do admit
applying the Poynting theorem is somewhat diffucult and transformer
manufacturers do not refer to it
at all, but then the makers of tennis rackets do not seem to refer to the
molecular makeup of nylon in their wares either, but the info is there for
those who wish to dig for it.....
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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