Re: strap primaries

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 3/1/02 10:14:40 AM Eastern Standard Time, tesla-at-pupman-dot-com
writes:


>
> Hey guys, A question about primaries.
>
> I once read that copper strap has better RF conductive properties than 
> copper tube, but we use tube in Tesla primaries to suppress corona 
> loss. My question is why? If you have, say, a peak primary voltage of 
> 40 kV and a 10 turn primary, don't you technically only have 4kV/turn? 
> Isn't 4 kV too low a voltage for corona discharge to really be a 
> problem? I would rather use strap as it is much easier to bend then 
> tube.
>
> Cheers,
>
> Greg Peters
> Department of Earth Sciences,
> University of Queensland, Australia
> Phone: 0402 841 677
> http://www.geocities-dot-com/gregjpeters



Hi Greg,
         You are right about the voltage per turn being fairly low. However,
the charge distribution along the primary depends on its geometry. Just as a
toroid with one or more sharp points/edges on the surface tends to cause
breakout at those locations, the sharp edges of strapping encourages corona at
those points. If you have to tune in to less turns, the effect becomes more
pronounced. If the voltage is lower, these "edge effect" coronal losses are
lower, but the gap losses are higher. One must therefore balance the
availability of materials, ease of fabrication, etc., against a possibly higher
power loss. 
         Perhaps a linear programming guru could find an analytical way to
choose the best balance?
         Hope this helps,
Matt D.
G3-1085