Re: [femm] How to get the leakage inductance when very bad coupling and litz wires.

[David Meeker <dmeeker@xxxxxxxx>]

David Meeker wrote:

> Be careful that sum the impedances correctly. If you have split one
> turn several wires, each of which carries part of the current in the
> turn, you have to add the all of the impedances of the wires that make
> up the turn in parallel, i.e.
>
> Zturn = 1/(1/Zwire1 + 1/Zwire2 1/Zwire3 + ...)
I think I messed this up--things are actually a bit more subtle than 
than this. The wires that make up a turn of Litz wire are transposed so 
that every wire in the turn sees about the same impedance. To account 
for this transposition, one could say that the impedance of each wire in 
a turn is the average of the impedance of each of the wires in that 
turn. The average impedance of each wire is added in parallel to get 
the impedance of the complete turn. This would imply:

Zturn= (Zwire1 + Zwire2 + Zwire3 + ... + ZwireN) / N^2

where there are N wires in a turn and Zturn is the combined impedance 
for all the wires in a turn. Zwire is the impedance of a particular 
wire from the axisymmetric finite element analysis where "circuit 
properties" have been applied to force the current to be distributed 
equally among all the wires in the turn.

Dave.

--
David Meeker
dmeeker@xxxxxxxx
http://femm.berlios.de/dmeeker