[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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



Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 12:17 PM 8/4/2005, you wrote:
Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Jim,

Is there something here that is uniquely different?? Are we talking about the field strength at the point of origin for the lightning or the average field strength??

Gerry R.

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 02:35 PM 8/3/2005, you wrote:
Original poster: "Denicolai, Marco" <Marco.Denicolai@xxxxxxxxxxx>

Hello Jim, all,

Based on my readings there are 3 different situations for breakdown:

- small gaps (some cm), Efield required 30 kV/cm, breakdown with avalanche (Townsend).
- 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.


These phenomena are very well documented, although usually with different names and in not such a clear manner. So, for a 2 m breakdown you need a 30 kV/m on the toroid surface, then at least some 5 kV/m within 1 m from it and the rest of the travel will succeed if 1 kV/m can be ensured.

Indeed... for instance, lightning typically starts in a field of a few kV/m.

Bazelyan and Raizer have a fair amount of description of breakdown conditions in non-uniform fields at high voltages, although not such a nice table as you have created.

That's observed field at the ground before a lightning strike (typical numbers are in the few kV/meter, but sometimes as high as 20kV/m). Calculations of the overall field (i.e. the voltage difference between cloud and ground divided by the height of the cloud) can actually give lower numbers. (B&R say hundreds of V/m)


Obviously, it's tough to measure this sort of thing accurately (especially when there are spatial variations), so there's a fair amount of uncertainty.

What's important is that it's nowhere near 3MV/meter, although, the field "somewhere" must be greater than 3MV/meter or the lightning wouldn't start in the first place.