Re: current in slot conductors

["David Meeker" <dmeeker@xxxxxxxx>]

--- In femm@xxxxxxxxxxxxxxx, "ahmad_m_eid" <ahmad_m_eid@xxxx> wrote:
> Dear all
> 
> I work in linear generator field. I want to consider an ac current
> moving in the coils, so, how can I define this current value??
> 
> if the rms value is 20 A and the number of turns/slot = 25
> 
> so, the define current will be 20 A or 20*25 in each slot?

It isn't entirely clear to me whether you want to look at a snapshot
in time, or whether you really want to run a harmonic analysis. In
any case, you can define the current in a region in one of two ways:

1) You can assign a "source current density" for a region. When you
have a wound coil, it's best to define the conductivity for the region
to be zero, so you don't have eddy currents redistributing and bucking
the source current. For DC problems, the current density that you'd
define would be (instantaneous current per turn)*(number of
turns)/(Coil cross-section area). For AC problems, FEMM assumes an
Amplitude, rather than RMS convention. You'd then define the current
density to be (instantaneous current Amplitude (i.e. RMS*sqrt(2)/2)
per turn)*(number of turns)/(Coil cross-section area). For AC
problems, you can split the current between real and imaginary parts
to give the currents the right phase with respect to time.

2) You can assign a "circuit property". This is really just a
constraint on the total current carried in a region or in a set of
regions. Again, for a wound coil, it's good to assign the
conductivity to be zero. You'd then define the total current to be
(instantaneous current Amplitude (i.e. RMS*sqrt(2)/2) per
turn)*(number of turns)

Dave.