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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
large.
Fascinating post. Any chance a copy of the book could be procured for
me?
Regards,
Malcolm