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.

Back-emf and flux linkage - Simple question!!!

Please login with a confirmed email address before reporting spam

Greeting Everyone

In the model I am sending, I would like to know how can I measure the flux linkage of the coils! and the afterwards the back-emf!!

I will be very thankfull if somebody can help me!!


1 Reply Last Post 4 mai 2010, 15:20 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 4 mai 2010, 15:20 UTC−4
Hi

Well for me the induced voltage is the integration of the electric field E_Phy around one loop, so I would use

Sudomain integration one one coil (i.e. 39 at time 0.1[s]) with the "compute volume integral checked"

Ephi_emqa/Area

which gives me some 4.11[mV], Area is defined as the integration of "1" over the coil area. The voltage is the electric field times the loop length = 2*pi*r

If I integrate the same subdomain to get the total current by integrating "Jiphi_emqa" I read -82.7[A] (this time witout the volume integration checked).
This should obey Ohms law R[Ohm] = rho[Ohm*m]*L[m]/(A[m^2]) = L[m]/(A[m^2])/(sigma[S/m])
and if I integrate over the same sundomain the value

1/Area^2/sigma_emqa

this time with the volume integration as I want the loop length included, I get some 50[uOhm] and I see that this corresponds to Ohms law. U=R*I

For me this is the best you can get to the back EMF or induced voltage from the magnetic field variation, and it is very similar to what is described in the generator examples in the acdcmodel.pdf document.

Do you agree ?, pls check carefully, ideally with a simpler example that you can check analytically

Have fun Comsoling
Ivar
Hi Well for me the induced voltage is the integration of the electric field E_Phy around one loop, so I would use Sudomain integration one one coil (i.e. 39 at time 0.1[s]) with the "compute volume integral checked" Ephi_emqa/Area which gives me some 4.11[mV], Area is defined as the integration of "1" over the coil area. The voltage is the electric field times the loop length = 2*pi*r If I integrate the same subdomain to get the total current by integrating "Jiphi_emqa" I read -82.7[A] (this time witout the volume integration checked). This should obey Ohms law R[Ohm] = rho[Ohm*m]*L[m]/(A[m^2]) = L[m]/(A[m^2])/(sigma[S/m]) and if I integrate over the same sundomain the value 1/Area^2/sigma_emqa this time with the volume integration as I want the loop length included, I get some 50[uOhm] and I see that this corresponds to Ohms law. U=R*I For me this is the best you can get to the back EMF or induced voltage from the magnetic field variation, and it is very similar to what is described in the generator examples in the acdcmodel.pdf document. Do you agree ?, pls check carefully, ideally with a simpler example that you can check analytically Have fun Comsoling Ivar

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.