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Re: Wood

Terry, Alex, All,

As Terry points out below, wood is used in many H-V
applications, even to this day.  The best wood for this
purpose is called Sitka Spruce, and only comes from
Alaska (where it grows naturally.)  Unfortunately, this
type of wood is *very* expensive; much more then almost
any other kind of wood product.  But its closed-cell/
smooth grain physical properties, and the fact that once it
is properly kiln dired and sealed with a good varnish, it
is virtually inpenetratable to ambient moisture.  Also,
believe it or not, this type of wood has a realitively low
dielectric loss tangent and high dielectric strength.

If you go to my web site, www.ttr-dot-com, and bring up 
Model 13, please see the white paper I wrote on its construction.  
The choice of using this wood product for both the master oscillator 
and the extra coil, are discussed at length.  Plus, there are some
nice photos, showing the method of construction, as well
as diagrams, referred to at the end of the article.

Best regards,

Bill Wysock.

> Date:          Wed, 12 May 1999 18:38:18 -0600
> To:            tesla-at-pupman-dot-com
> Subject:       Re: Wood
> From:          Tesla List <tesla-at-pupman-dot-com>

> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> 
> Hi Alex,
> 
> Most people are surprised to learn that wood is commonly used in large
> distribution transformers and other high voltage devices filled with oil
> even in these "space age" times.  Despite today's fancy plastics, wood will
> last indefinitely in such applications and has been well proven for over
> 100 years now.  
> 
> Wood may have a problem absorbing moisture which makes it "too" resistive
> and it can flashover.  Soaking it with oil vastly reduces this and I would
> think it would actually work better than many plastics since its surface is
> rather rough.  I have heard that it's very slight conductivity also reduces
> static charges building up on the surfaces and thus renders it even better
> at resisting flashover.  Since it is slightly conductive, it is not good
> for holding static charges but TCs usually have so much power going through
> them that this is not noticed.
> 
> The real problems I can see are not knowing how much water content there is
> and thus not being able to be sure it is ok.  The oiled surface my also
> pick up dirt that may hurt it's standoff.  Also, I wonder if plywood would
> fall apart after soaking in oil and the glues my do something unforeseen to
> the voltage standoff.  Oak is a very good choice but I would stay away from
> pine due to the high sap content.  Hard maple is very strong and can be
> worked to high precision but it would saturate with oil slowly.  Of course,
> the kiln dryed types are what you want.  Here in Colorado, it is very dry
> and I use wood a lot for high voltage stuff.  In a humid area, I would
> worry much more.  Oil soaking solves this problem if one can stand having
> everything being all oily.
> 
> Wood soaked with oil will burn, so you have to design and use it with that
> in mind.  An advantage is that if you use the right kind of oil, the fumes
> will not be very toxic unlike most plastics.
> 
> Of course, wood is cheap, very easy to get, and there are all kinds of
> wonderful tools available for working with it...
> 
> 	Terry
>  
> 
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