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Leakage inductance vs. self inductance

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bpelec

Electrical
Jul 12, 2005
54
In a transformer, is the leakage inductance of a winding equal to its self inductance?

 
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No, those terms are not interchangeable.

Self inductance is a term associated with a linear transformer model that includes 3 elements: L1, L2 (self inductances), L12

Leakage inductance is a term in a power transformer model. It includes elements L1, L2 (leakage inductances), Lm, possibly some resistances, and an ideal power transformer (different than ideal linear transformer).

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The linear transformer model is governed by equations something like:
V1 = l1*di1/dt + M * di2/dt
V2 = l2*di2/dt + M * di1/dt

The ideal power transformer (part of the real power transformer model discussed above) is governed by
V1 = a:V2 where a is turns ratio

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Electricpete, Thank you for your help. I can tell that I must have got myself confused...

The reason why I asked this question is because I need to calculate the leakage inductances for a power transformer. Unfortunately, I can only find equations that calculate the self and mutal inductances of coils - using the Neumann formula... I thought if the leakage inductance basicly refers to all the flux that does not link the two coils through the core, ie flux that flows through the air around the individual coils, then the leakage inductance would be equal to the self inductance of the individual coil... I hope that makes some sense...

Do you know a way of calculating leakage fluxes in a transformer, based upon the geometry of the transformer?

Thanks!
 
"I thought if the leakage inductance basicly refers to all the flux that does not link the two coils through the core, ie flux that flows through the air around the individual coils"

Yes, that is correct. If you want to call it self-inductance, ok, but that term I have only heard in the context of a different model (linear model vs power transformer model). I have never heard of Neumann and I don't know how to calculate leakage inductance from geometry (other than Phi*N/I where Phi is the leakage flux and I is the associated current). I think I could dig up a way to calculate it from tests on the assembled transformer if you want that info.

If you want to calculate it based on the geometry and you get no responses here, you might get more help in the magnetic forum.

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It is very possible that I have my terms confused, but it seems that I am thinking about it in roughly the right way...

Unfortunately, I do need to calculate the leakage inductance from the geometry, so I may well try the magnetic forum as you suggest...

Thank you again for all your help!

 
I've just posted a couple of links to some publications in thread238-132623. If you have some basic data about your core structure you should be able to calculate the leakage inductance. The method used in Snelling's book gave results which were shown under test to be within a few percent of the calculated value for a shell-type core in 3C8 grade ferrite.


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