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Problem with modeling coil
Posted Jul 5, 2010, 11:53 a.m. EDT 3 Replies
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Hi!
I'm trying to model coil with 38 windings. I have defined also current of 260[A]. My coil is without core and is made as simple rectangle with size 0.38[m] x 0.037[m]. Current density is 7e5[A/m^2]. You can see that in the model which I attache below.
I should obtain H = 26000[A/m]. But my Magnetic Field is about 1082[A/m]. What is wrong with my model?
Only when I set freqency at 0 (direct current), value of H is correct. But I need to set alternating current. Somone told me that induced current is too high.
Thanks for help,
Przemek
I'm trying to model coil with 38 windings. I have defined also current of 260[A]. My coil is without core and is made as simple rectangle with size 0.38[m] x 0.037[m]. Current density is 7e5[A/m^2]. You can see that in the model which I attache below.
I should obtain H = 26000[A/m]. But my Magnetic Field is about 1082[A/m]. What is wrong with my model?
Only when I set freqency at 0 (direct current), value of H is correct. But I need to set alternating current. Somone told me that induced current is too high.
Thanks for help,
Przemek
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3 Replies Last Post Aug 5, 2010, 4:31 a.m. EDT
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Posted:
1 decade ago
Hi
I have currently only my 4.0a running so I'm not sure how correctly it translates your 3.5a model, but there is a few things to check
the total coil area is 0.38*0.037=0.01406m^2 for 38*260=9880A hence your 702.7kA/m^2 we agree
if you do a static analysis you get from COMSOL some emqa.normH=24.36kA/m that corresponds to your estimate, COMSOL is normally not calculating wrong (at least not my 4.0a).
Now in harmonic analysis (Frequency domain) you are at default 50Hz and you have some skin effects that might change things.
If I use the V4 "Multiturn coil model, use a sigma of 57E6[S/m] N=38 I=260[A] coil section =0.00037 m^'2 (fill factor 100%) I get a results as 24.46kA/m in static mode and also in frequency Domain at 50Hz.
So if I clear all your 3.5 resuls and recalculate with the bulk coil I get emqua.normH=1269 A/m as you we agree
Now if you integrate the current density Phi over the coil area I get 52.2-504.97i [A] for your bulk coil and 9880[A] for the multi-turn coil (as the effect of the Multi Turn Coil Boundary is to correct for induced voltage drop etc to force the current to the expected value.
All this tells me that you are not considering the skin effects and the induction effects in the physics, and that for your coil analysis, you should rather switch to V4 as here you have the multitur coils physics already implemented. If not you must add a variable or weak form to force the current to overcome the induction effects
hope this helps
Have fun Comsoling
Ivar
I have currently only my 4.0a running so I'm not sure how correctly it translates your 3.5a model, but there is a few things to check
the total coil area is 0.38*0.037=0.01406m^2 for 38*260=9880A hence your 702.7kA/m^2 we agree
if you do a static analysis you get from COMSOL some emqa.normH=24.36kA/m that corresponds to your estimate, COMSOL is normally not calculating wrong (at least not my 4.0a).
Now in harmonic analysis (Frequency domain) you are at default 50Hz and you have some skin effects that might change things.
If I use the V4 "Multiturn coil model, use a sigma of 57E6[S/m] N=38 I=260[A] coil section =0.00037 m^'2 (fill factor 100%) I get a results as 24.46kA/m in static mode and also in frequency Domain at 50Hz.
So if I clear all your 3.5 resuls and recalculate with the bulk coil I get emqua.normH=1269 A/m as you we agree
Now if you integrate the current density Phi over the coil area I get 52.2-504.97i [A] for your bulk coil and 9880[A] for the multi-turn coil (as the effect of the Multi Turn Coil Boundary is to correct for induced voltage drop etc to force the current to the expected value.
All this tells me that you are not considering the skin effects and the induction effects in the physics, and that for your coil analysis, you should rather switch to V4 as here you have the multitur coils physics already implemented. If not you must add a variable or weak form to force the current to overcome the induction effects
hope this helps
Have fun Comsoling
Ivar
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Posted:
1 decade ago
Thank You very much for reply.
I'm sorry I'm answering so late but I would like to say that very usefull for modeling multi-turn coils is solution from COMSOL's Knowledge Base no. 916.
In COMSOL 3.5a there is some problem with skin effect and induced currents. Just applying current as current density on the conductor we get improper results. To obtain proper computation we have to apply current indirectly using loop potential as described in solution number 916.
I'm sorry I'm answering so late but I would like to say that very usefull for modeling multi-turn coils is solution from COMSOL's Knowledge Base no. 916.
In COMSOL 3.5a there is some problem with skin effect and induced currents. Just applying current as current density on the conductor we get improper results. To obtain proper computation we have to apply current indirectly using loop potential as described in solution number 916.
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Posted:
1 decade ago
Hi
I beleive this is what has been added in the single turn and multiple turn boundary conditions in V4 for AC/DC
--
Good luck
Ivar
I beleive this is what has been added in the single turn and multiple turn boundary conditions in V4 for AC/DC
--
Good luck
Ivar