Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Measuring of induced voltages in externally excited coils
Posted Aug 7, 2015, 9:51 a.m. EDT Low-Frequency Electromagnetics Version 5.0 3 Replies
Please login with a confirmed email address before reporting spam
Hey,
my next challenge consists of simulating a quasi-static problem of this model in frequency domain. I want some of my cylindrical coils generating an AC field (driven by an AC current) and measure the induced voltage in the saddle coils which are penetrated by the generated time-varying magnetic flux. Perhaps you could give me a hint how to do that? A stationary study step runs without any errors but simply adding a frequency domain study step seems not to be the solution of the problem since my simulation does not converge (the error in my convergence plot of the BiCGStab oscillates between 10^-3 and 3) at certain frequencies (25 kHz). I tried to simulate with f = 1 kHz to foreclose an insufficient mesh. In this case I got another error message: "Failed to find a solution. Matrix has zero on diagonal. Returned solution is not converged."
I hope anybody is able to help me again. Thank you in advance.
Sebastian
my next challenge consists of simulating a quasi-static problem of this model in frequency domain. I want some of my cylindrical coils generating an AC field (driven by an AC current) and measure the induced voltage in the saddle coils which are penetrated by the generated time-varying magnetic flux. Perhaps you could give me a hint how to do that? A stationary study step runs without any errors but simply adding a frequency domain study step seems not to be the solution of the problem since my simulation does not converge (the error in my convergence plot of the BiCGStab oscillates between 10^-3 and 3) at certain frequencies (25 kHz). I tried to simulate with f = 1 kHz to foreclose an insufficient mesh. In this case I got another error message: "Failed to find a solution. Matrix has zero on diagonal. Returned solution is not converged."
I hope anybody is able to help me again. Thank you in advance.
Sebastian
3 Replies Last Post Aug 18, 2015, 4:24 a.m. EDT
Please login with a confirmed email address before reporting spam
Posted:
9 years ago
Hi,
The convergence error that you are getting here is most likely due to the zero electrical conductivity in the air-region around the conductor. You would need a small value for electrical conductivity of air whenever you solve the Magnetic Fields physics in the Frequency Domain in 3D.
To get the induced voltage in the saddle coil, the easiest approach would be to assign the saddle coil as "Multi-Turn Coil" and put the current excitation to be zero (open circuit). The induced voltage in the coil will be available for post-processing. See the following example, in which the induced voltage in the coil due to magnet oscillating next to it is simulated.
www.comsol.com/model/voltage-induced-in-a-coil-by-a-moving-magnet-14163
Hope this will be useful.
Best Regards,
Nirmal Paudel
The convergence error that you are getting here is most likely due to the zero electrical conductivity in the air-region around the conductor. You would need a small value for electrical conductivity of air whenever you solve the Magnetic Fields physics in the Frequency Domain in 3D.
To get the induced voltage in the saddle coil, the easiest approach would be to assign the saddle coil as "Multi-Turn Coil" and put the current excitation to be zero (open circuit). The induced voltage in the coil will be available for post-processing. See the following example, in which the induced voltage in the coil due to magnet oscillating next to it is simulated.
www.comsol.com/model/voltage-induced-in-a-coil-by-a-moving-magnet-14163
Hope this will be useful.
Best Regards,
Nirmal Paudel
Please login with a confirmed email address before reporting spam
Posted:
9 years ago
Hi Nirmal,
you made my day. Thank you very much. My first try failed because I set the electrical conductivity to sigma = 1e-7 S/m. When I set it to sigma = 1e-1 S/m the simulation ran. The real average conductivity of air is in the range of about 10^(-15) S/m [see "Effect of relative humidity and sea level pressure on electrical conductivity of air over Indian Ocean" by S. D. Pawar, P. Murugavel and D. M. Lal, 2009, DOI: 10.1029/2007JD009716] so I can't see why my first try did not work properly. Is it because of numeric constraints? I hope I will find a configuration in which the simulations will give me a hint of how the reality will look like.
I would like also to thank you for your very interesting example in which I found the possibility to get the induced voltage property of all multi-turn coils.
Thank you very much and have a nice day,
Sebastian
you made my day. Thank you very much. My first try failed because I set the electrical conductivity to sigma = 1e-7 S/m. When I set it to sigma = 1e-1 S/m the simulation ran. The real average conductivity of air is in the range of about 10^(-15) S/m [see "Effect of relative humidity and sea level pressure on electrical conductivity of air over Indian Ocean" by S. D. Pawar, P. Murugavel and D. M. Lal, 2009, DOI: 10.1029/2007JD009716] so I can't see why my first try did not work properly. Is it because of numeric constraints? I hope I will find a configuration in which the simulations will give me a hint of how the reality will look like.
I would like also to thank you for your very interesting example in which I found the possibility to get the induced voltage property of all multi-turn coils.
Thank you very much and have a nice day,
Sebastian
Please login with a confirmed email address before reporting spam
Posted:
9 years ago
Hello,
unfortunately my problem is not solved yet completely. I redcued my model to minimum required elements and the result of the simulation is not comprehensible. Certainly some of my boundary conditions are wrong but I can't find the reason.
My model (comsol_model_reduced_induced_voltage___four_exc_coils_clearedsolution.mph) consists of a Helmholtz coil pair (the distance does not match the radius exactly so it is not a real Helmholtz coil pair) where each coil is seperated into two discs. Therefore I added four multi-turn coil subnodes to my "Magnetic Fields" node - each of them describes one of the Helmholtz coil parts. In the center for the Helmholtz coil pair there is a saddle coil pair. The whole configuration is symmetric. When I compute the study containing current coil calculation steps and a frequency domain step (f = 1kHz to 25kHz) the resulting magnetic field is symmetric, too. In an additional 1D plot group I plotted the induced voltages of both saddle coils but they differ from one another (that's not possible).
When I remove one of the seperated discs (comsol_model_reduced_induced_voltage___inner_exc_coils_clearedsolution.mph and comsol_model_reduced_induced_voltage___outer_exc_coils_clearedsolution.mph) both induced voltages are (more or less) the same (like it should be). What is wrong with my double disc Helmholtz coil approach (comsol_model_reduced_induced_voltage___four_exc_coils_clearedsolution.mph)?
I would be very grateful if there is someone who has a solution for this problem and/or the time to take a look at my model (I had to clear the solutions because of the file sizes).
Thanks in advance and have a nice day,
Sebastian Draack
unfortunately my problem is not solved yet completely. I redcued my model to minimum required elements and the result of the simulation is not comprehensible. Certainly some of my boundary conditions are wrong but I can't find the reason.
My model (comsol_model_reduced_induced_voltage___four_exc_coils_clearedsolution.mph) consists of a Helmholtz coil pair (the distance does not match the radius exactly so it is not a real Helmholtz coil pair) where each coil is seperated into two discs. Therefore I added four multi-turn coil subnodes to my "Magnetic Fields" node - each of them describes one of the Helmholtz coil parts. In the center for the Helmholtz coil pair there is a saddle coil pair. The whole configuration is symmetric. When I compute the study containing current coil calculation steps and a frequency domain step (f = 1kHz to 25kHz) the resulting magnetic field is symmetric, too. In an additional 1D plot group I plotted the induced voltages of both saddle coils but they differ from one another (that's not possible).
When I remove one of the seperated discs (comsol_model_reduced_induced_voltage___inner_exc_coils_clearedsolution.mph and comsol_model_reduced_induced_voltage___outer_exc_coils_clearedsolution.mph) both induced voltages are (more or less) the same (like it should be). What is wrong with my double disc Helmholtz coil approach (comsol_model_reduced_induced_voltage___four_exc_coils_clearedsolution.mph)?
I would be very grateful if there is someone who has a solution for this problem and/or the time to take a look at my model (I had to clear the solutions because of the file sizes).
Thanks in advance and have a nice day,
Sebastian Draack
Attachments: