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Currents and reverse currents
Posted Oct 24, 2011, 10:03 a.m. EDT 1 Reply
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Hi
I'm all new to COMSOL, and have a couple of questions it probably is straight forward to answer for a somewhat more experienced user. Im currently doing some 2D simulations on electric current distribution for various frequencies (<300Hz). Im using magnetic and electric fields (mef) and I'm specifying my currents using Surface current condition on the outer border of the are I want to contain the current within (dividing total current by the circumference, acc. to amperes law), first of all it would be great if some could give me a pointer if this should somehow be wrong, but the results seem to make sense (I want the current to go into/out from the screen). If I specify surface on a boundary so it contains an enclosed area, if I have different materials and shapes inside this boundary, the current should distribute according to conductivity (+ skin/proximity effect etc), normal current division that is, am I right? Also, I try to confirm my results by performing a surface integration to obtain the total current, however the result is not consistent with the current Itot i set in the surface current condition (Itot/2*pi*r). Comments on this?
My real problem however is when I have a total current flowing in one direction as specified by the surface current condition along the border of my domain, and at the same time have a conductor (in real life an insulated cable) with current flowing in the opposite direction (all currents are along z-axis) inside the same cross sectional area. How do i specify this? I've tried with two separare surface current density conditions, but it seems one simply overrides the other, the results are at least not consistent.
Last, with two parallell cables (simulating at 100 Hz) I would expect a proximity effect, i do not get consistent results on this one either. When setting currents with opposite directions, I would expect the proximityeffect to cause a higher current density on the side facing the other cable (right hand side of the left conductor and vice versa), but instead the case is the exact opposite. When the currents have the same direction and amplitude, I get no proximity effect at all, with a current distribution as for a single conductor with skin effect.
I really hope someone can help me out here. The model is not very sophisticated, but I need to understand these principles before I move on to my real model.
Thanks a lot in advance!
I'm all new to COMSOL, and have a couple of questions it probably is straight forward to answer for a somewhat more experienced user. Im currently doing some 2D simulations on electric current distribution for various frequencies (<300Hz). Im using magnetic and electric fields (mef) and I'm specifying my currents using Surface current condition on the outer border of the are I want to contain the current within (dividing total current by the circumference, acc. to amperes law), first of all it would be great if some could give me a pointer if this should somehow be wrong, but the results seem to make sense (I want the current to go into/out from the screen). If I specify surface on a boundary so it contains an enclosed area, if I have different materials and shapes inside this boundary, the current should distribute according to conductivity (+ skin/proximity effect etc), normal current division that is, am I right? Also, I try to confirm my results by performing a surface integration to obtain the total current, however the result is not consistent with the current Itot i set in the surface current condition (Itot/2*pi*r). Comments on this?
My real problem however is when I have a total current flowing in one direction as specified by the surface current condition along the border of my domain, and at the same time have a conductor (in real life an insulated cable) with current flowing in the opposite direction (all currents are along z-axis) inside the same cross sectional area. How do i specify this? I've tried with two separare surface current density conditions, but it seems one simply overrides the other, the results are at least not consistent.
Last, with two parallell cables (simulating at 100 Hz) I would expect a proximity effect, i do not get consistent results on this one either. When setting currents with opposite directions, I would expect the proximityeffect to cause a higher current density on the side facing the other cable (right hand side of the left conductor and vice versa), but instead the case is the exact opposite. When the currents have the same direction and amplitude, I get no proximity effect at all, with a current distribution as for a single conductor with skin effect.
I really hope someone can help me out here. The model is not very sophisticated, but I need to understand these principles before I move on to my real model.
Thanks a lot in advance!
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1 Reply Last Post Oct 25, 2011, 2:50 a.m. EDT
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Posted:
1 decade ago
Hi
first of all if you are not looking at induced current, you could use MF rather than MEF (at least to start with, you do not really need to solve for V and the solver will converge quicker ;)
second why use current only on the border, and not let COMSOL show you the skin effect correctly ? Have you studied the model library (do not forget to do an update) ACDC Verification models Paralle wires ?
--
Good luck
Ivar
first of all if you are not looking at induced current, you could use MF rather than MEF (at least to start with, you do not really need to solve for V and the solver will converge quicker ;)
second why use current only on the border, and not let COMSOL show you the skin effect correctly ? Have you studied the model library (do not forget to do an update) ACDC Verification models Paralle wires ?
--
Good luck
Ivar