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Tranformer Flux Density of Core

04/07/2010 5:37 AM

I was going through a specification of power transformer & had the following doubt.

Is there is any maximum limit value for this two parameters?

1) Maximum flux density in the core (Tesla).

2) Current density of the coil - material copper.

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#1

Re: Tranformer Flux Density of Core

04/07/2010 6:54 AM

Yes and yes. The maximum flux density will depend on the material, perhaps 1500 Gauss for some ferrites, perhaps 14 000 Gauss for some steels, etc. You just have to look at the material curves and see where they saturate (The BH curve starts to bend over).

Current density depends on temperature rating and the efficiency of the design in getting heat out. Somewhere in the 10 mA·mm-2 to 20 mA·mm-2 range you'll start to see the "magic smoke" escaping your transformer. You should have some general guidelines based on the required regulation rather than maximum current density.

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#2
In reply to #1

Re: Tranformer Flux Density of Core

04/07/2010 9:51 AM

Somewhere in the 10 mA·mm-2 to 20 mA·mm-2 range

Yes, I remember reading about a guy having temperature Mega problems, in a very confined environment (something like 10 cubic millimeter). And the currents he was handling were in the range of 10 milliAmpere to 20 milliAmpere.

How the history repeats itself....

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#3
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Re: Tranformer Flux Density of Core

04/08/2010 5:46 AM

Is the surface in this 10 mA/mm2 the surface of the outside of the coil, the surface that can "radiate" heat? Or what surface have you in mind ?

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#4
In reply to #3

Re: Tranformer Flux Density of Core

04/09/2010 2:44 PM

Il s'agit de la densite du courent dans le cuivre du transformateur. 10mA/mm2 c'est une ridicule densite, je croie que l'ecrivent voulait dire 10 A/mm2.

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#5
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Re: Tranformer Flux Density of Core

04/11/2010 11:08 AM

Je pensait que pour un moteur electrique la densité était environ 8 à 13 Ampère par milimètre carré de cuivre. Et pour un transformateur, (parce qu'il n'y a pas un ventilateur au derrière du transformateur) le courant est limité à 3 ou 4 A/mm2.

Est-ce que c'est juste ?

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#7
In reply to #5

Re: Tranformer Flux Density of Core

04/11/2010 3:55 PM

Vous avez raison, pour les diferent formes et bobinages, la densite permissible varies, je crois, de 3 a 10 A/mm2. Je me rapele que, pur un instrument avec un cadre mobile, la densite est reduite, au desous 100 mA, pour eviter le chaufage. Je ne sais pas quelles sont les valeures pour les grands transformateurs. Ils ont leur refroidisment donc, je pense, la densite peut etre elevee.

On a ete bon d'exercer mon peuvre bagage de langues "etrangeres"

A la bon chance.

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#6
In reply to #4

Re: Tranformer Flux Density of Core

04/11/2010 12:08 PM

Yes, yes, of course I did.

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#8

Re: Tranformer Flux Density of Core

04/14/2010 10:04 AM

Limit of Flux Density depends on Core Material like for M4 Grade your limit shoulb 1.86.

For Current Density your limit should be 4.3 for safe design

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