Re: Skin Effect... and More(croft

Subject:        Re: Skin Effect... and More(croft
       Date:    Mon, 28 Apr 1997 17:40:06 +1200
       From:    "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Organization:   Wellington Polytechnic, NZ
         To:    tesla-at-pupman-dot-com

Hi Bert,
>        From: Bert Hickman <bert.hickman-at-aquila-dot-com>
> Organization: Stoneridge Engineering
>          To: Tesla List <tesla-at-pupman-dot-com>
>  References: 
>             1
> Malcolm, Alfred, and all,
> There's even more wierdness associated with Skin Effect! It turns out
> that some current actually does penetrate the conductor's interior. With
> increasing depth, the magnitude of this current decreases, AND the phase
> is continually retarded. What this really means is that it's possible
> that after a certain depth of penetration, current may actually be
> flowing in a direction OPPOSITE to that on the surface(!). In such a
> case, the effective AC resistance of the conductor would be decreased by
> removing the inside part of the conductor - a copper tube will show less
> AC resistance than a solid copper rod! This effect _actually occurs_ in
> high current busbars coming off the generators at 60 Hz in big power
> plants 

That is very interesting. I settled on a rule of 3 skin depths for 
secondary wire diameter as it seemed that using much larger copper
was not only running into diminishing returns resistance-wise but also
reducing inductance unreasonably. For example, I calculated that a 
total diameter of 8 skin depths was just about the practical limit 
for reducing resistance but using that wire gauge, inductance is 
slashed to around 1/4 of its value. Now it seems from what you are 
saying that one would actually be going backwards by using wire that 

Fascinating post. Any chance a copy of the book could be procured for