Re: Official air breakdown voltage?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 08:54 AM 11/27/2005, you wrote:
> Original poster: "JT Bowles" <jasotb@xxxxxxxxxxx>
>
> I say you are correct. Mostly. Voltage requirements for dielectric 
> beakdown, in this case atmosphere, are linear, at slow-pulse DC

Not precisely true (and on this list, being careful with your wording 
is important, to avoid confusion.)

Breakdown voltage for a uniform field gap (or one that closely 
approximates it, as in large spheres separated by a distance much 
less than their radius) is roughly linear as a function of the 
product of distance and density  (aka Paschen's law).




> From what I have been reading lately, AC voltage requirements for 
> the same dielectric are often much higher. Thus, we can conclude ac 
> requires a much higher voltage to generate, say 1' arcs, than dc does.

Where have you been reading this?  I wouldn't conclude this, and 
neither would most other researchers in the field of HV breakdown, so 
that "we" might be a bit overstated.

First.. are you talking gas dielectrics or any?  Are you talking 
gases at atmospheric pressure?  Which gases? (recombination time 
varies with the gas).

There are some "rise time" effects.. If you shoot a real fast pulse 
in, it might not breakdown because the pulse is over before the spark 
has time to develop.   The same kind of thing is true for RF 
breakdown.. if the field reverses before the ionized atom/electron 
has time to collide with another to start an avalanche, then the 
spark might not progress very far.

If you are interested in really learning about spark breakdown.. I'd 
recommend you find a copy of "Spark Discharge" by Bazelyan and 
Raizer.  It will set you back perhaps $100 or so, brand new, so a 
library might be a better strategy.

Another good book might be Cobine, Gaseous Conductors, which talks 
about spark breakdown, although more oriented towards arcs with some 
stuff about glow discharges. this one was published by Dover in 
paperback for about $10, so it is cheaper on the used market.

The great lightning book by Martin Uman: "Lightning" also published 
by Dover (and, unlike Cobine, it's still in print) has a fair amount 
of stuff on discharge processes.

For HV stuff in general, a good "free" start is the High Power 
Microwave Transmitter report by William North, which is on hot-streamer.com.
http://hot-streamer.com/TeslaCoils/OtherPapers/NorthReport/

Interlibrary loans can be real useful.

A bit of self education will go a long way to eliminating "foot in 
mount" disease..

Jim