Re: safety gaps on capacitors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "The Big Giant Kevin by way of Terry Fritz <twftesla-at-qwest-dot-net>" <neo4s-at-hotmail-dot-com>

Simple safety gaps (not impedance current limited) placed across your tank 
capacitor can cause the capacitor to fail due to a mechanism known as 
Blumlein Inversion Generator.  The capacitor is usually a long pair of foil 
strips with a dielectric between.  The fact that it is rolled up is not 
important.  This structure is a form of parallel wire transmission line. If 
you fully charge the line to some voltage X, then if you place a low 
impedance short circuit across one end of this line (the safety gap firing) 
you will create a pulse of reverse
polarity which will travel down the transmission line, adding to the 
original charge and appearing as 2X voltage at the other end.  You have just 
subjected your capacitors innards to the highest possible discharge current 
it can possibly produce with all the associated hydrodynamic stresses, and 
you have doubled whatever overvoltage condition you normally subject the 
capacitor to in Tesla use.  This is a proven formula for capacitor failure!
Safe use of a capacitor safety gap requires carefully matched series 
impedance to neutralize the Blumlein effect.

Rob


Just when you think its save to go back in the garage... I found a link to a 
site that talks about this effect.
http://www.kentech.co.uk/transmission_lines/Transmission_lines.html

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