Re: [femm] Power Factor

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

Bruce McGee wrote:

> Hi
>
> I am working on an induction heating problem. I induce currents from
> a source into a metal material for heating purposes. From the
> solution calculated by femm30 is it possible to determine the power
> factor of the load relative to the source.

Specify a purely real current in your conductor a "circuit" property. Then,
solve the problem and integrate A . J over the conductor. For convenience,
we could denote the result of this integral as X. The power factor would
then be:
-Im[X]/Abs[X].

This works because you can use the A.J integral to get sort of a
frequency-dependent inductance by dividing X by i^2, where i is the per-turn
current in the coil:

L=X/(i^2)

The voltage that's needed to drive the current is:

v = j*omega * L * i

just like a normal inductor. If you split L into real and imaginary parts (
L=Lr + j Li) and expand the above,

v=j*omega*Lr*i - omega Li*i

so Lr is associated with reactive power, and Li with real power.

Dave.


begin:vcard 
n:Meeker;David
tel;fax:781-890-3489
tel;work:781-684-4070
x-mozilla-html:TRUE
url:http://members.aol.com/dcm3c
org:Foster-Miller, Inc.;Electrical and Electronic Systems Group
version:2.1
email;internet:dmeeker@xxxxxxxxxxxxxxxxx
title:Senior Engineer
adr;quoted-printable:;;350 Second Avenue=0D=0A;Waltham;MA;02451-1196;USA
fn:David Meeker, Ph.D.
end:vcard