Re: PFC Question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Ed, variac users,

On 6 Nov 2005, at 11:15, Tesla list wrote:

> Original poster: Ed Phillips <evp@xxxxxxxxxxx>
>
> "Hi Dmitry,
>
> I hope you're correct, however, the performance curves from powerstat
> may suggest otherwise.  I'm having a hard time understanding how there
> can't be any series inductance when, say, the setting as at the midway
> point.  Maybe you or someone else can explain this.
>
> Gerry R. "
>
>     Easy.  The transformer has very close to unity coupling factor so
> the leakage inductance is close to zero.   Do a Google search on those
> terms for a better explanation.
>
> Ed

In an ideal world yes, one would like a variac to have perfect
coupling between all turns. Due to its required geometry however it
can't. The turns are spaced out in a single layer around a toroidal
core. Closest to unity coupling is only obtained by having all
windings occupying the same space, a physical impossibility but one
you can get close to with a single bobbin'd transformer wound on an E-
I core or a potcore with interleaved windings. In the same breath
it's worth saying that even interleaving has its problems - the
better the coupling obtained between primary and secondary turns the
worse becomes the coupling of each winding to itself.

Malcolm