very long sparks

• To: tesla-at-pupman-dot-com
• Subject: very long sparks
• From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Wed, 05 Jan 2000 11:37:47 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

The longest artificial sparks that I am aware of were NOT produced by a
tesla coil, but were produced by (very) large impulse generators. Les
Renardiers group in France built a generator in the 8-9 MV range which
produced long sparks (I'd expect >50 meters, but I don't have the reference
handy), and in Bazelyan and Raizer ("Spark Discharge") there is an
impressive photo of a 100+ meter (thats meters, folks, not feet) spark in
an outdoor test lab. Put it this way, the spark is much longer than the
height of a standard looking HV transmission tower..

As a practical matter, once you get above about a megavolt, the linear
distance/voltage relationship goes away (mostly because you are in a
non-uniform/needle gap situation).  Not much voltage increase gets you a
very large distance increase. This is of great concern to those designing
EHV substations because the clearance distances get phenomenal.  At these
voltages, the amount of energy behind the spark (mostly from Ctop in your
Tesla coil) determines how far it can propagate.

Greg Leyh's Electrum made fairly long sparks (20 meters?) and Bill Wysock's
big coils that kVA Effects ran last year(?) also could make sparks in this
range, but this is using pretty much state of the art components
(particularly caps, wire, and forms). I doubt that you'd get much farther
unless you basically built some sort of high-rep rate impulse generator.

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