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

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 04:14 PM 8/3/2005, you wrote:
> Original poster: Steve Conner <steve@xxxxxxxxxxxx>
>
>
>
> > - medium gaps (< 1 m), Efield required 5 kV/m, breakdown with 
> > stable streamers and final jump.
> > - large gaps (> 1 m), Efield required only 1 kV/m, breakdown with 
> > leader-streamer phases and final jump.
>
> Does this explain why big coils are more efficient than little ones? 
> Once you get beyond 1 metre of streamers, it looks like you need 5x 
> less electric field to keep it growing.
>
> Steve Conner


Exactly that... once you've got a streamer that is long enough, 
relative to the terminal, it looks like a wire hanging in space, and 
further growth is more determined by the energy available to keep the 
channel hot, and to build up enough charge at the end of the wire to 
get the field above breakdown for the next jump.

A small TC just can't store enough energy in the top load to keep the 
channel hot as it gets fairly long.

In the electric power business it sort of ties in with voltage too... 
At low voltages (hundreds of kV), the field is fairly easy to control 
by making the radius of curvature of conductors large enough, so the 
spark never gets started. The safe clearance distance is roughly 
linear with voltage.  But when you get in the MV range, conductors 
are impractically large (30cm radius is BIG), so you have a 
non-uniform field, and the gap that the spark will jump gets longer 
much faster than linear.  Apparently, this wasn't real well 
understood in the early days of 700kV line development, and 
unexpected flashovers and faults were the result.