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Roughly how much leakage inductance in "section" wound transformer?

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treez

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Hello,
We are doing a 2.8kW offline LLC converter..

Vin = 390VDC
Vout = 180VDC
F(SW) = 91kHz

We have done a section-wound LLC transformer, and the main reason for this was because when restricted to using round sectioned enamelled copper wire, “sectioned” winding more easily facilitates achieving lower winding resistance.

However, do you know what the likely leakage inductance term (seen from primary) would be for this sectioned winding configuration?

We need a total of 100uH for the resonant inductor, and we expect that to be comprised of some leakage inductance and some external inductance.

How much do you think the leakage inductance term will be?

(The transformer diagram and LLC schematic are attached.)
 

Attachments

  • LLC transformer.pdf
    27.3 KB · Views: 112
  • Schematic _Full Bridge LLC converter.pdf
    18.2 KB · Views: 131

Often it is around the 7-8% mark for this construction, so .07 * 941 = 65uH... approx
 

Post #20 of this below thread seems to show that the actual leakage inductance tends to be about three times more than the inductance of the primary if it were in air..

https://www.edaboard.com/threads/350032/

Now the primary has just 28 turns in this case, so 28 turns in air, I would have thought, would have a very low inductance indeed.
In fact this website…
https://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml
…makes it about 20uH. –so multiplying this by three gives 60uH.

Easy Peasy was right.

Mind you, FvM's example was (non-interleaved) concentric would pri and sec, whereas in my case, i have separate section wound pri and sec, so i wonder how much more leakage i will get?
 

my experiments with transformer on etd29:
w1=32; w2=2
separator width =1.5mm Lm=500u Ls=63u
separator width =3.0mm Lm=500u Ls=80u
 
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