safety gap

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>


> Original poster: Steve Ward <steve.ward@xxxxxxxxx>

> Hi Dmitry,

>>> unfortunately according to B & R at fast rise times the electric
>>> strength of the air gaps may be  several times higher than at LF, so
>>> it seems it`s impossible to make a gap, that helps in such case :-(

> That is interesting!  Do they offer any figures on the increase in
> electric strength vs. rise time?  Maybe the effect is small at TC
> frequencies?  And do they know why this happens?

why do you say "at TC frequencies"? the frequency is of no matter here
- we speak about the _rise times_, coz we`re talkin about primary
strike - it`s just a capacitive discharge.

today i`ve found this:

http://www.pupman.com/listarchives/1996/october/msg00470.html

"Since Paschen's law is basically a statement of continuity ( The number of
electrons leaving the anode must equal the number injected into the gap at the
cathode.) there is a time delay between the application of voltage and gap
breakdown.   The breakdown voltage increases with the rate of rise of the
applied voltage.  The ratio of the static to the dynamic breakdown voltage is
called the Surge Ratio."

sounds logical for you as an aswer "why this happens"?

you may want also look into this document:

"Evaluation of commercial surge suppressors"

http://www.eeel.nist.gov/817/817g/spd-anthology/files/Evaluate%201963%20SPDs.pdf

"The gaps are characterized by their volt time performance; some are quite
successful in producing a "flat" curve, i.e., the breakdown voltage at short
times (0.1 us) is not a large multiple of the breakdown voltage at
DC.
[...]

Ratio of 0.1 us breakdown to min. breakdown:

160%
250%
Not defined
600%
140%
over 400%
[...]"

i`ll be interested in your comments.

-----
I have never heard of a coiler blowing up a pole pig!  A pole pig can
easily blow up a coiler, however.  You could also be hit by a bus though.
27-08-96 (c) Richard Hull, TCBOR