Re: About leakage inductance in transformers

Terry Given wrote:
MassiveProng wrote:

On Sun, 04 Mar 2007 15:18:47 +1300, Terry Given <my_name@xxxxxxxx>
Gave us:


MassiveProng wrote:

On 3 Mar 2007 10:03:02 GMT, Robert Latest <boblatest@xxxxxxxxx> Gave
us:



John Larkin wrote:



With the secondary shorted, the core has essentially no effect,


I think the leakage inductance still depends on permeability.


It probably will, but not much, since the shorted secondary is doing its damnedest to keep flux out of the core.




In order for ANY energy to pass from the primary to the secondary,
it MUST pass through the core. Perhaps you were making some vague
reference to stored energy?


nope. If they are wound concentric (and possibly interleaved) then there is still plenty of coupling, sans core.



That depends on the frequency. The lower it gets, the less coupling
will occur without a core.


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
.

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