About leakage inductance in transformers

[MassiveProng]

Sans core, coupling is defined solely by geometry.

And it certainly doesnt depend on frequency, high or low.

You would change your mind seeing what happens as a core is even
moved near such a configuration.

What I said is true, because at RF frequencies there are plenty of
"transformers" that have no core included. Funny how I never see such
a setup at low frequencies.

Want to try again?

 

[The Phantom]

That and similarly leaky constructions are common nowadays...

http://www.premmagnetics.com/SPW050d.htm

because of safety isolation standards.

John

Look at the aspect ratio of the Prem xfmrs and compare to the Wikipedia
drawing. The only time I've ever seen a transformer with the secondary as far
from the primary as in the Wiki drawing is the horizontal output (flyback)
transformer in a television.

 

[Terry Given]

buggered if I know what happened to my post, so here it is again (kinda):


That is completely wrong.

Sans core, coupling is defined solely by geometry.

Dear linguistically challenged person, "sans" means "without"

You would change your mind seeing what happens as a core is even

moved near such a configuration.

this is noting that the presence of a core increases coupling.

Which has no relevance to your erroneous assertion that coupling in the
absence of a core is frequency-dependant!

What I said is true, because at RF frequencies there are plenty of

"transformers" that have no core included. Funny how I never see such
a setup at low frequencies.

Want to try again?

sure, easy:

the reason you dont see coreless transformers used at low frequencies is
because the resultant low inductances have (by definition) low impedance
at low frequency, thereby causing large magnetising currents to flow,
which is usually inconvenient.

It has everything to do with Xl = jwL, and nothing to do with coupling
being a function of frequency, which it isn't.


BTW It is possible to make 50/60Hz mains transformers with very little
core material - just a post inside the concentric windings. Of course
the magnetising inductance is low, so Imag is high, and they puke flux
everywhere, but the core losses are extremely low (what with there being
mostly no core), and the overall result can be cost-effective.

And it certainly doesnt depend on frequency, high or low.

If you dont believe me, go read Grover. Not that you'll understand it.
Or you could try Magnetic Circuits and Transformers, MIT rad lab series.
Given your demonstrated lack of understanding, Smit & Wijn will confuse
the hell out of you, and of course Perry is so far out of your league it
isnt even worth mentioning

(NB: at very low frequencies, the currents associated with low
inductances will eventually exceed the capability of the source, thereby
convincing the gullible that coupling has changed; at high frequencies
capacitive coupling will swamp inductive coupling, again leading the
foolish to the same erroneous conclusion; at really high frequencies
things get quite interesting, but for practical transformers its fair to
neglect displacement current)


This makes two MassivelyWrong posts re. magnetics, in relatively short
order. Give up.

Cheers
Terry

 

[MassiveProng]

BTW It is possible to make 50/60Hz mains transformers with very little
core material - just a post inside the concentric windings. Of course
the magnetising inductance is low, so Imag is high, and they puke flux
everywhere, but the core losses are extremely low (what with there being
mostly no core), and the overall result can be cost-effective.

Bwuahahahahahahaha!

 

[Terry Given]

Bwuahahahahahahaha!

its called a partial-core transformer.

http://www.ewh.ieee.org/r10/nzs/IEEENZS_Postgrad_Presentations_2006.pdf

contains a brief description of such a device.

Prof. Bodger at Canterbury University, NZ, has done a lot of work on these.


Cheers
Terry

 

[Harry Dellamano]

its called a partial-core transformer.

http://www.ewh.ieee.org/r10/nzs/IEEENZS_Postgrad_Presentations_2006.pdf

contains a brief description of such a device.

Prof. Bodger at Canterbury University, NZ, has done a lot of work on
these.


Cheers
Terry

Terry, responding to MassiveWrong is like trying to piss into the wind, it
all comes back in your face.
Cheers,
Harry

 

[Terry Given]

Terry, responding to MassiveWrong is like trying to piss into the wind, it
all comes back in your face.
Cheers,
Harry

wrt the diatribes, sure.

I thought others might be interested in partial core transformers though.

and its funny to see just how little he really knows about transformers

Cheers
Terry

 

[Jim Thompson]

wrt the diatribes, sure.

I thought others might be interested in partial core transformers though.

and its funny to see just how little he really knows about transformers

Cheers
Terry

It's not funny how little he knows... such a big mouth for such a
little brain.

...Jim Thompson

 

[Terry Given]

It's not funny how little he knows... such a big mouth for such a
little brain.

...Jim Thompson

Indeed.

On a related note, I asked someone a little while ago why the "oral
minority" who crap on about morality always seem to get caught sticking
there peckers in the wrong places (eg pastor Ted et al). The response?
people see themselves in others. The virtuous assume others are
virtuous, so see no need to proselytise. The corrupt see corruption,
thus spout off about it (at least until they get caught, then they tend
to shut up, fast).

Methinks a similar argument explains MassivelyWrongs frequent "your all
retards" outbursts.

Cheers
Terry

 

[Jim Thompson]

[snip]

It's not funny how little he knows... such a big mouth for such a
little brain.

...Jim Thompson

Indeed.

On a related note, I asked someone a little while ago why the "oral
minority" who crap on about morality always seem to get caught sticking
there peckers in the wrong places (eg pastor Ted et al). The response?
people see themselves in others. The virtuous assume others are
virtuous, so see no need to proselytise. The corrupt see corruption,
thus spout off about it (at least until they get caught, then they tend
to shut up, fast).

Methinks a similar argument explains MassivelyWrongs frequent "your all
retards" outbursts.

Cheers
Terry

I think that's a universal reality. When I was a teenager the easiest
lay was truly the preacher's daughter... named "Faith", naturally.
Thus the standing twist on an old phrase, "Keep the baby, Faith" ;-)

...Jim Thompson

 

[MassiveProng]

It's not funny how little he knows... such a big mouth for such a
little brain.

Yet you retarded fucks still contend that placing a gap in a
transformer core is not ever done.

Real good, boys. You are all batting zero!

 

[MassiveProng]

Methinks a similar argument explains MassivelyWrongs frequent "your all
retards" outbursts.

Cheers
Terry

It's YOU'RE, you stupid ****.

 

[Terry Given]

[snip]

It's not funny how little he knows... such a big mouth for such a
little brain.

...Jim Thompson

Indeed.

On a related note, I asked someone a little while ago why the "oral
minority" who crap on about morality always seem to get caught sticking
there peckers in the wrong places (eg pastor Ted et al). The response?
people see themselves in others. The virtuous assume others are
virtuous, so see no need to proselytise. The corrupt see corruption,
thus spout off about it (at least until they get caught, then they tend
to shut up, fast).

Methinks a similar argument explains MassivelyWrongs frequent "your all
retards" outbursts.

Cheers
Terry

I think that's a universal reality. When I was a teenager the easiest
lay was truly the preacher's daughter... named "Faith", naturally.
Thus the standing twist on an old phrase, "Keep the baby, Faith" ;-)

...Jim Thompson

Beautiful! Thanks for the laugh, Jim.

Cheers
Terry

 

[John Larkin]

Look at the aspect ratio of the Prem xfmrs and compare to the Wikipedia
drawing. The only time I've ever seen a transformer with the secondary as far
from the primary as in the Wiki drawing is the horizontal output (flyback)
transformer in a television.

But the effect of the core permeability on leakage inductance will be
severe for such a non-concentric structure.

John

 

[Terry Given]

Yet you retarded fucks still contend that placing a gap in a
transformer core is not ever done.

Real good, boys. You are all batting zero!

I defy you to demonstrate such a claim, or to paste the relevant text;
its just not there.

You have consistently demonstrated a thorough lack of understanding of
magnetics and their design.

Cheers
Terry

 

[Terry Given]

It's YOU'RE, you stupid ****.

*THAT* is the best possible refutation you can make of my statements re.
magnetics design? Pathetically peurile posturing prat!

Terry

 

[The Phantom]

It's even stranger than that. If the secondary resistance
(Rs+Rl, or just Rs if you set Rl to zero) is less than w*Ls, then
the Effective Rpri will decrease with decreases of Rs. If the
secondary resistance is greater than w*Ls, then Rpri will
*increase* with decreases of Rs.

Sorry about the delay in replying to this post, piddling
about with sums on scraps of paper. That effective Xpri
is not[/QUOTE]

perhaps the word "necessarily" should be inserted here; at a high enough
measurement frequency it's pretty close. We just need to pick w so that
(w.Ls)^2 >> (Rs)^2 in the denominator above.

the leakage inductance and I can now see where the
frequency-sensitive values for Rpri and Xpri come from.

Excellent. This is what I was trying to bring to the attention of the group.
That the secondary resistance causes the measured Lpri to increase at low
frequencies seems to not be commonly understood. The plots I posted over on
ABSE show the effect clearly. To get an accurate result, one needs to either
make the measurement at a high enough frequency that (w.Ls)^2 >> (Rs)^2, or
calculate it as L(leak) = Lp.(1-k^2). By the way, we've all heard of the term
"coupling coefficient" for the quantity k = m^2/(Lp*Ls). Additionally, I saw in
the 1943 book I mention elsewhere that the expression (1-k^2) is called the
"leakage coefficient".

The problem starts with the fact the the only definition
of leakage inductance is based on a transformer without
any winding resistance.

Lp(leak)
+---+ +-----+ +--///---+---+ +-----+
| M | | | |
) ( 2 ) )|( Ratio =
Lp ) ( Ls ----> k.Lp ) )|( 2
) ( ) )|( k .Lp/Ls
| | | | |
+----+ +-----+ +---------+---+ +----+

The Lp-M-Ls transformer can be represented by an equivalent
circuit of an uncoupled inductor, Lp(leak), value being given
as Lp.(1-k^2), a shunt inductor of value (k^2.Lp) and a
perfect transformer with inductance ratio k^2.Lp/Ls.

The coupling, k is of course defined by k^2 = M^2/Lp.Ls.

Ok, now add the winding resistances, Rp and Rs to the
equivalent circuit and the short circuit on the secondary.

Rp Lp.(1-k^2) Rs
+---/\/\--///---+---+ +---------/\/\--+
| | | |
) )|( Ratio = |
k^2.Lp ) )|( |
) )|( k^2 .Lp/Ls |
| | | |
+----------------+---+ +---------------+

Now transform Rs over to the primary side.


Rp Lp.(1-k^2) R= Rs.k^2.Lp/Ls
+--/\/\---///---+----/\/\---+
| |
) |
k^2.Lp ) |
) |
| |
+---------------+-----------+

Now convert the parallel L//R into the series-equivalents
to make it easy to see Effective Rpri and Lpri.


(w.k)^2.Rs.Lp.Ls
Rp Lp.(1-k^2) Ra Ra = ---------------
+--/\/\---///------/\/\---+ Rs^2 + (w.Ls)^2
|
)
La ) (w.k.Ls)^2.Lp
) La = ----------------
| Rs^2 + (w.Ls)^2
+-------------------------+

Effective Rpri = Rp + Ra.

Effective Lpri = Lp.(1-k^2) + La.

But Ra and La are both frequency sensitive.

In fact if you expand-out Ra and La in Rpri and Lpri
you get back to Wm Fraser's originals, complete with
the required minus sign in the Lpri calculation.





As above. Lp(leak) = Lp.(1-k^2), where k^2 = M^2/Lp.Ls.

Quite right. Using this relationship, one can adjust the mearurement made at
a too low frequency and thus obtain a much better value for the leakage
inductance. It is not a perfect compensation, but it's a lot better than no
compensation at all. Given the difficulty of making accurate measurements on
iron cored transformers, it's probably as good as you're going to get.

This should be understood by every engineer who ever measures leakage
inductance.

The rest is a red herring, swimming up a blind alley.

In the book I mention elsewhere is an interesting tidbit. The term:

(w^2.M^2)
------------------- in the expression for Effective Xpri is equal to
(Rs)^2 + (w.Ls)^2


the square of the open circuit voltage ratio; that is, (Eoc1/V2)^2, where Eoc1
is the voltage measured at the open circuit primary when a voltage V2 is applied
to the secondary.

 

[The Phantom]

But the effect of the core permeability on leakage inductance will be
severe for such a non-concentric structure.

John

I don't think it's that bad, but anyway it's an acceptable tradeoff. When the
output of the secondary is 30 kV, you can't let said secondary get very close to
anything.

I have one of those lying around; I'll have to make some measurments on it.

 

[John Perry]

...

Terry, responding to MassiveWrong is like trying to piss into the wind, it
all comes back in your face.

....but as long as you can put up with it, I'm enjoying learning more
about magnetics than I thought I ever could.

I am, of course, editing out the MP crap from the good stuff you guys
are feeding me.

Thanks,

John Perry

 

[Harry Dellamano]

...but as long as you can put up with it, I'm enjoying learning more
about magnetics than I thought I ever could.

I am, of course, editing out the MP crap from the good stuff you guys
are feeding me.

Thanks,

John Perry

I agree totally John. Every system has noise and a little noise can
sometimes improve performance but too much is just disruptive. MW has no
respect for others so how can we have any respect for him. Sounds like a
smart tech that never became an engineer.
Cheers,
Harry