[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Leakage inductance



Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi!

On Sat, 5 Oct 2002, Tesla list wrote:
> Original poster: "Kamil by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<tcmail-at-poczta.fm>
> I want to ask if there is any method to calculate leakage inductance of
> transformer when I know physical dimensions. I mean fairrite core
> transformer (not shunted)- U type core, 9cm^2 core cross section, window
> 35x85mm, outside dimensions: 79x129mm, 50mm thick. Primary:10 turns,
> sec: 680 turns. I know that this data are not enough for calculation
> (leakage inductance depends on windings shape, distance from the core,
> etc.).

Sounds good for a lot of kilowatts! :)

Calculating leakage inductance I think is not trivial...
  http://www.intusoft-dot-com/mag.htm
(it's way beyond hobbyist budget, i've never used it)

But, what exactly are you trying to do?
Do you want to minimize leakage, or get it to match a specific value you
have in mind?

If just minimizing (and assuming you're running with a non-gapped UU
core), then very good coupling between the windings will help a lot!
Like, if possible, split the primary and place the secondary in between:

 ------------
  ########## pri
 ------------
  ########## sec
  ##########
 ------------
  ########## pri
----------------
 ....core.....

It reduces leakage, but OTOH this will put more voltage stress on the
insulation... With your 1:68 turns ratio, you maybe target 15kVac out?
so proper insulation will be a bit, errm, complicated...

Or just split the pri & sec combos into two pairs, one pair onto each of
the UU core legs. And center-tap-to-ground the secondary => voltage stress
reduced to half => insulation thickness can be reduced. Of course this
works only if you still have enough core winding area...

Anyway, to "answer" your question... With your 10 turn primary and core
that large of size, the leakage inductance is maybe around 100uH (0.1mH)
or so. Just a guess, and not necessarily correct. :-)

If you have already wound the transformer, you can measure the leakage
inductance by shorting the secondary and measuring the inductance accross
the primary.

 http://www.voltech-dot-com/Downloads/ATAppNotes/104-105-0-5A.pdf

Easy to do, and if leakage indutance turns out to be "too much" then you
have the "fun" task of re-designing the transformer... ;-)


Ok! good luck for designing!

greetz,

 - Jan

--
*************************************************
 high voltage at http://www.hut.fi/~jwagner/tesla
 Jan OH2GHR