Re: calculating safe primary turn-to-turn distance

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

> 
> Original poster: "Malcolm Watts" <M.J.Watts-at-massey.ac.nz> 
> 
> > Original poster: "Stan" <sdarling-at-columbus.rr-dot-com> 
> > I have been curious since I started doing Tesla coils about this:  how
> > does one calculate the minimum air distance of turn to turn spacing in
a
> > primary for a given voltage?  I'm not an EE so my common sense tells me

> 
> You're right - and certainly not stupid. An easy approach is 
> to divide the peak primary voltage you will ever run the coil 
> with by the number of turns to get a volt/turn gradient. You 
> can base spacing on that but there is a catch - turn-turn 
> flashover will most likely occur at the insulating supports as 
> tracking over the insulators is a favoured path for a spark to 
> follow. So spacing should really take this into account rather 
> than the airgap between the turns.
> 


A good rule of thumb is that creeping breakdown occurs at 1/3 the voltage
as free air breakdown.. that is, allow an inch of creepage/surface for
every 20 kV.