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calculate resistance of a numeric multi turn coil in freqency domane is to high

Posted Jun 24, 2013, 10:10 a.m. EDT Low-Frequency Electromagnetics Version 4.3b 2 Replies

Viktor Reising
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Dear all,
I hope anybody in this Forum have the same exipiriance width the multi turn coil damane.
In my model i have a simple numeric multy-turn-coil domane. My problem is that the calculate resistance in freqency domain is to high. In my example the resistance is 60Ohm and in reel its not more then 1,3Ohm. If we loock to another coil example in comsol, so we see the same problemm. Everytime we have wrong calculated resistance of the coil in frequency damain. The problem is the voltage drop(real component not imaginary), the voltage drop is to high. The problem exist in numeric, circular calculation in the coil.

So please hep me to fixt this problemm.
best regards Viktor Reising
2 Replies Last Post Jul 31, 2013, 3:58 a.m. EDT
Viktor Reising
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Posted: 1 decade ago Jun 25, 2013, 5:19 a.m. EDT
dear all,
unfortunately nobody could help me so far. So I had to ask the support. If anyone has the same problem. Thus, this response of the support should perhaps be helpful.



Dear Viktor,

The Coil Resistance variable in Frequency Domain is computed as the ratio between the coil Voltage and Current. The voltage is, in turn, computed by integrating the electric field in the coil, so the accuracy of the resistance depends ultimately on the accuracy of the electric field.

Unfortunately, especially at low frequencies, the real part of the electric field distribution tends to be dominated by noise. This is a consequence of the omega^2*epsilon term in the equation being relatively small.

Now, as long as you can neglect the real part of the electric field (in other words you do not consider any conductive materials), you can get a much more accurate resistance if you make its definition consider only the imaginary part of the field. In practice, what you need to do is enter the Equation View of the Multi-Turn Coil Domain 1, and change the expression for mf2.VCoil_2 to the following (please see the attached screenshot "equation.png":

mf2.mtcd2.R*mf2.ICoil2-j*imag(mf2.mtcd2.Vind)

Now the resistance shows a much lower value (around 0.08 ohm) that confirms the analytical solution.

I hope this will help you. Please let us know if you have further questions.


after the changes the real component voltage drop of the coil not so high. The resitanse is not exact but better then before.

best regarbds
Viktor
dear all, unfortunately nobody could help me so far. So I had to ask the support. If anyone has the same problem. Thus, this response of the support should perhaps be helpful. Dear Viktor, The Coil Resistance variable in Frequency Domain is computed as the ratio between the coil Voltage and Current. The voltage is, in turn, computed by integrating the electric field in the coil, so the accuracy of the resistance depends ultimately on the accuracy of the electric field. Unfortunately, especially at low frequencies, the real part of the electric field distribution tends to be dominated by noise. This is a consequence of the omega^2*epsilon term in the equation being relatively small. Now, as long as you can neglect the real part of the electric field (in other words you do not consider any conductive materials), you can get a much more accurate resistance if you make its definition consider only the imaginary part of the field. In practice, what you need to do is enter the Equation View of the Multi-Turn Coil Domain 1, and change the expression for mf2.VCoil_2 to the following (please see the attached screenshot "equation.png": mf2.mtcd2.R*mf2.ICoil2-j*imag(mf2.mtcd2.Vind) Now the resistance shows a much lower value (around 0.08 ohm) that confirms the analytical solution. I hope this will help you. Please let us know if you have further questions. after the changes the real component voltage drop of the coil not so high. The resitanse is not exact but better then before. best regarbds Viktor

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Denis Maus
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Posted: 1 decade ago Jul 31, 2013, 3:58 a.m. EDT
Hi,

if you have a magneticaly coupled System you can also calculate the Resistance of the coil by integrating the resistive losses then devide it by (rms current)^2 of each component and then sum up.

Regards,
Denis
Hi, if you have a magneticaly coupled System you can also calculate the Resistance of the coil by integrating the resistive losses then devide it by (rms current)^2 of each component and then sum up. Regards, Denis

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