Re: [femm] Circuits in FEMM

["you se-ho" <sxy28@xxxxxxxxxxx>]

To Dear Everyone:

How are you? Again some conceptual questions that makes me confused.

(1) I think the gradient term comes out from the displacement term in the 
Maxwell's equation. In class, when the conductors are good conductor, we are 
usually told that the term can be ignored. Is it true when frequency is high 
so skin effect is outstading?

(2) If I send the +1A one one conductor and get back -1A the other 
conductor, should the resistive loss (I guess this is from power loss, and 
the power is also 0.5*I^2*R where I=1A ) be same as the impedance (or its 
real part only) on each conductor?

(3) Is there any way to use the impedance in the circuit property for Spice 
circuit input (i.e frequency independent parameter R) ?

Any comments will be appreciated
Sincerely,
SE-HO YOU

================
frank.e.lenning@xxxxxxxxxx wrote:

How does the circuits feature in FEMM work for multiple conductors?
Let's say I have two conductors of different materials that I define
with Circuits to be carrying a total current of 1 amp together. How
does FEMM solve this problem? Does it iteratively solve the problem
by choosing different deltaV's for each conductor until it gets the
right total current or is there some easier way that it uses to set
the deltaV's? It appears to get the right answer, I'm just trying to
understand how.


It's best to visualize this situation as being like two resistors driven in 
parallel. For two resistors driven in parallel, the voltage drop across 
each resistor is the same, so to get a given total current, you just have to 
pick the right voltage drop. In femm, the situation is analogous. For your 
model where you have two conductors labeled with the same circuit property, 
the voltage gradient is the same for each conductor. The program just has 
to pick the applied voltage gradient to give the right total current for the 
conductors. For magnetostatic problems, there is enough information to do 
this calculation up front, before doing anything else. For harmonic 
problems, eddy currents induced in the conductors have an effect on the 
total current, so the program ends up solving an extra equation for the 
voltage gradient that is required for each circuit to enforce the circuit's 
current constraint.
In any case, you can choose View|Circuit Props off of the main menu of the 
postprocessor to see what voltage gradient was required to enforce the 
circuit's current constraint, from which the program also infers impedance.

Dave Meeker






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frank.e.lenning@xxxxxxxxxx wrote:

> How does the circuits feature in FEMM work for multiple
> conductors?
> Let's say I have two conductors of different materials that I define
> with Circuits to be carrying a total current of 1 amp together. 
> How
> does FEMM solve this problem?  Does it iteratively solve the problem
> by choosing different deltaV's for each conductor until it gets the
> right total current or is there some easier way that it uses to set
> the deltaV's?  It appears to get the right answer, I'm just trying
> to
> understand how.
>  
>  
It's best to visualize this situation as being like two resistors driven
in parallel.  For two resistors driven in parallel, the voltage drop
across each resistor is the same, so to get a given total current, you
just have to pick the right voltage drop.  In femm, the situation
is analogous.  For your model where you have two conductors labeled
with the same circuit property, the voltage gradient is the same for each
conductor.  The program just has to pick the applied voltage gradient
to give the right total current for the conductors.  For magnetostatic
problems, there is enough information to do this calculation up front,
before doing anything else.  For harmonic problems, eddy currents
induced in the conductors have an effect on the total current, so the program
ends up solving an extra equation for the voltage gradient that is required
for each circuit to enforce the circuit's current constraint.

In any case, you can choose View|Circuit Props off of the main menu of the postprocessor to see what voltage gradient was required to enforce the circuit's current constraint, from which the program also infers impedance.

Dave Meeker
 

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