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



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.