> reduce the "leakage" flux, then we are at an impass, until it is
> cleared up.
flux path. Reduction of leakage would depend on the spacing between
primary and secondary, and the spacing between these and the core, as
well as the distribution of the windings around the core- your
interleaved windings on a toroid are an approach to that. Somehow, the
fact that there is a need for insulation is also a factor.
I have had some thoughts about this and I missed the most important
factor which makes my answer wrong.
First of all -using Faraday there is a direct relationship between the
applied voltage of the primary and the total flux (phi)enclosed.This
flux can be all in the core, partly in the core or outside the core.
This is independent of the core. However, relative permeability and the
flux paths determine the distribution. Now suppose that the core
permeability approaches infinity. The magnetic flux doesn't change as it
is tied to the applied voltage.
Now B=muH or H=B/mu and this implies that the H approaches 0 in the
core. Total NI magnetizing also approaches 0 and that means that the
integral of H.dl along any and all flux paths linking this winding so
the for a path that is not fully in the core the flux goes to 0. That
is- no leakage flux.
Loading the secondary doesn't change this situation.