*If you think using an iron core with infinite permeability would*

> reduce the "leakage" flux, then we are at an impass, until it is

> cleared up.

> 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.