I cant tell you that but I will tell you what I believe.
when you place one set of windings on top of another, such as in a standard transformer, reasonable coupling is obtained, whereas when the windings are wound together such as in bifilar and hexfilar windings the coupling is superior. The main reasons for not using multifilar windings are:-
1) ease of manufacturing
2) It is not practical for step up and step down applications
Of course this relates to cost and is fine where magnetic coupling is the only factor.
There are advantages in inductance manipulation with these types of windings. http://en.wikipedia.org/wiki/Bifilar_winding
Litz wire is described here http://en.wikipedia.org/wiki/Litz_wire
I'm sure you know most of what I put above, and now for something not proven as it is a part of radiant energy theory.
Imagine you charge a wire with a negative charge, all other negative charges will be repelled and all positive charges will be attracted. Electroscopes demonstrate this principle. http://en.wikipedia.org/wiki/Electroscope
This causes electrical energy and charged particles in the environment to polarize. For an instant there is a movement of charge in the vicinity of our wire. The theory is that some of this movement will be picked up in multifilar wire and so for an instant we have a moving charge or what we call available power. Exactly the same thing occurs when we discharge our wire but of the opposite polarity. There is also some talk about this energy having an extremely small mass causing an overshoot ie momentum, again a potential source of dynamic charge.
There are many claims about this and also some anomalies in electrical practice that could be explained by this. Some work has been done in the early part of the last century to prove it too. I cant think what it was called but the experiment went something like this. A wire was placed in a vacuum chamber and pulsed at high voltage. The pulse was very abrupt and created via a spark gap and Tesla coil. Detection equipment was able to show something assumed to be energy entering and leaving the wire. The experiment was similar to what Tesla did when he created discharges from his coils and we are not talking about the famous sparks.
This is not the experiment, but a picture of one of Tesla's experiments showing the type of thing that they found http://www.villesresearch.com/images/teslacone.jpg
The difference being that they produced it in a vacuum, so it had nothing to do with ionic particles or plasma. The phenomenon occurred both at the charge and the discharge of the wire and was not visible to the naked eye but was visible to the detection equipment.
Its interesting that I cant find any reference to the experiment now, but that might just be me that is putting the wrong key words into the search.
As I say this is all theory and has not been proved to modern sciences criteria, but if true it would explain some strange phenomenon. Hope this helps
One of my many musings on the aether here http://www.energeticforum.com/renewable ... post173026