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Self inductance of brooks coil

Posted 20.01.2011, 22:29 GMT-5 Low-Frequency Electromagnetics Version 4.0a 2 Replies

L. Queval
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Hi,
I am making some tests with Comsol 4.0a. I want for example to calculate the self inductance of a Brooks coil using the AC/DC module.

You can find more informations and geometry definition about Brooks coil here:
www.nessengr.com/techdata/brooks/brooks.html (I checked the formulas)

If we take,
c = 1 m
then the theoretical self inductance is,
L11 = 2.5491e-6 H

I set up a model similar to the "Helmholtz coil" tutorial (3D, mf, stationary with external current density) and tried to calculate the self inductance using the energy method,
L11=2*Wm/(I0^2)
where,
Wm is the total magnetic energy (mf.intWm)
I0 is the current in the coil

I got,
L11 = 6.1446e-7 H

This value is obviously different from the theoretical one. I enclosed my model if you want to have a look. Any solution ?

Attachments:

2 Replies Last Post 24.01.2011, 04:01 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 21.01.2011, 02:00 GMT-5
Hi

One little thing, as your J0 is defined w.r.t Parameters, you can also define it as a Parameter (former "Constants" and which are interpreted once at the beginning of a Solver run) the advantage is that you see the resulting value written out, which is often useful, and you can use the J0 as a parameter for a later "parametric sweep" if needed

When I take your model in v4.1 I get :

int3 H.B/(I0^2) (H)
2.4603e-6

Close enough no? Try with infinite elements to get perhaps closer, not even sure, or a finer mesh

But I have reset the mesh to default physics induced (normal), so probably its that there are still a few typos in the equations in V4.0, really use the latest patched 4.1, you will be less frustrated ;)

--
Good luck
Ivar
Hi One little thing, as your J0 is defined w.r.t Parameters, you can also define it as a Parameter (former "Constants" and which are interpreted once at the beginning of a Solver run) the advantage is that you see the resulting value written out, which is often useful, and you can use the J0 as a parameter for a later "parametric sweep" if needed When I take your model in v4.1 I get : int3 H.B/(I0^2) (H) 2.4603e-6 Close enough no? Try with infinite elements to get perhaps closer, not even sure, or a finer mesh But I have reset the mesh to default physics induced (normal), so probably its that there are still a few typos in the equations in V4.0, really use the latest patched 4.1, you will be less frustrated ;) -- Good luck Ivar
L. Queval
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Posted: 1 decade ago 24.01.2011, 04:01 GMT-5
Hi Ivar,
Thank you for pointing this out. With finner mesh and bigger sphere I got 2.5354e-6H as expected.
Thank you again.
Hi Ivar, Thank you for pointing this out. With finner mesh and bigger sphere I got 2.5354e-6H as expected. Thank you again.

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