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Old 15th April 2011, 01:36 PM   #1
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Default enclosing magnetic fields

I wonder about making an enclosure to contain magnetic fields . . .

Take a 50/60 Hz transformer that generates a relatively strong magnetic field. For discussion, let's put the transformer and magnetic field in a spherical enclosure made of 1/2" (13 mm) low carbon steel. A large number of the magnetic field lines are now contained within the steel. But now, let's say the enclosure is cut in half and, for disussion, there is something like a 1/4" (7 mm) gap between the two hemispheres. What does the magnetic field do at the gap (aperature) ? At the gap, do the field lines extend out basically as far as they would if there was no enclosure at all ?

Thanks for any ideas and information.


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Old 15th April 2011, 01:51 PM   #2
jcx is online now jcx  United States
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you could do a simplified sim with free fea software

Any Hall Effect gurus out there?

I think there is a axisymmetric solver in Quickfield
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Old 15th April 2011, 02:07 PM   #3
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And I thought that asking if anyone knew of a simulator would be asking too much. Thanks jc !

I'm now thinking that the field density will be just higher at the aperature, then it would without the enclosure.

Regardless, look forward to trying out QuickField. "No training required" : )


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Old 15th April 2011, 02:59 PM   #4
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Yes, I think the field would be higher at the aperture than if no enclosure were present, but it won't extend out very far.
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Old 16th April 2011, 03:04 AM   #5
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I think the resulting Gaussian flux of the "E X B" vector fields would result in a Poynting vector, eventually culminating in a myoptic black hole. From such things, worm holes and spatial warps and timespace discontinuities are formed.

Or I might be wrong. Perhaps nothing will happen.
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Old 17th April 2011, 12:03 AM   #6
seanvn is offline seanvn  Viet Nam
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It is always possible to do the experiment and find out that way.
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Old 18th April 2011, 02:33 PM   #7
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Call me crazy, but, I don't think strong magnetic fields (like the kind surrounding a power tranny), can be contained! Especially not with steel, which actually reinforces the field, because it presents an easier path than air. (Think of how cabinet door magnets are strengthened by the addition of steel plates.) This is why chassises are recommended to be built with non-ferrous metals.

On the other hand, mu-metal shields are used to keep flux out of mic-input transformers. But mu-metal is very expensive.

Perhaps I misunderstand the question? Is this a theoretical question only?
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Old 18th April 2011, 06:25 PM   #8
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The flux prefers to go through steel, so it avoids the air outside. This may strengthen the flux at gaps in the steel path, as already said, but these will be short-range fields. The steel in the transformer core is already doing this for flux inside the windings. The OP is considering exploiting the same physics for flux outside the windings.

Mu-metal is better then steel at this because it has such high permeability.
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