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Re: 20 joules at 100 bps vs 4 joules at 500 bps



Original poster: Greg Leyh <lod@xxxxxxxxxxx>



Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>

[snip]
> >and it seems that sphere protects the secondary worse than toroid:
> >http://www.lod.org/Projects/electrum/testing/pages/electrumeric.html
>
> You're correct --  a toroidal electrode would have provided far
> better field control than the spherical electrode used on
> Electrum.  The spherical electrode geometry was part of the overall
> aesthetic requirement however, and had to be accommodated.  As a
> result, the operating instructions for the machine specify to
> immediately remove power for 5 seconds if a tower strike is observed.
>
>So far, there has been no permanent surface tracking observed in
>Electrum's outer casing.

according to this photo:
http://www.lod.org/Projects/electrum/testing/images/electrum40kW3.jpg
does the secondary outer surfaces in touch with the sphere? but my
toroid would be mounted higher on the secondary top, then, as Antonio
said there wouldn`t be any problems:

"Reduction due to surface tracking  would apply if an insulating surface
were in contact with areas of the terminal where the electric field is
high, but this doesn't happen in  this case."


The physical connection between the electrode and secondary is recessed, for exactly this reason. Also, the diameter of the sphere shields the relatively sharp corner of the secondary, to an extent. I looked for corona off the top corner of the secondary coilform while I was in the sphere and couldn't find any, visually.


> Based on experience, 5kV/inch seems to be a reasonable surface
> gradient to maintain on the outside of a secondary form.

200kv/m it is in straight way, and if it would be like that:
http://www.lod.org/Status/90L10KPhotos.htm
maybe this value would be more? for example Conner`s 30" secondary
flashes at about 600kv.

Yes, 200kV/m and higher gradients are attainable, in clean, dry laboratory conditions. Often times we must operate in less than ideal conditions however, such as these:
http://www.lod.org/Projects/120L50K/austin01.jpg
http://www.lod.org/Projects/120L50K/Graz40kW.jpg
Such environments submit the coilform to high moisture content, smoke, particulates and atomized diesel. Note that utility companies are even stingier than 5kV/inch with their surface gradients -- a 12kV utility insulator is often over 7 inches long.


-GL