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*To*: tesla-at-pupman-dot-com*Subject*: Re: spark gap voltages (Secondary capacitance)*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Fri, 24 May 2002 17:43:21 -0600*Resent-Date*: Fri, 24 May 2002 17:43:33 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <DfXeD.A.G1B.jAt78-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net> One could use a rod gap, which is a deliberately nonuniform field, and one for which tables have been published. http://home.earthlink-dot-net/~jimlux/hv/rodgap.htm Of course, the rod itself will greatly reduce the voltage the TC reaches.. Tesla list wrote: > > Original poster: "Dave Larkin by way of Terry Fritz <twftesla-at-qwest-dot-net>" <teslaman15-at-hotmail-dot-com> > > > > A small DC supply is used to charge the primary cap, until the spark gap > > > breaks down. The output spark length under these conditions _is_ > >(almost) a > > > direct relation of voltage. So if a ground terminal with a large ROC > >(to > > > try and make the field a bit more uniform) is used and the single shot > >spark > > > length measured, one can determine the approximate output voltage, using > >the > > > fact that air breaks down at ~1MV/meter for large gaps. > > > >The correct figure is 30 kV/cm for parallel planes, or terminals where > >the radius of curvature (R) is much larger than the distance between the > > I am well aware that the textbook breakdown for air is 3MV/meter. > 1MV/meter is a crude approximation to account for the fact that the field is > seriously non-uniform. The equation you posted below seems a much better > way of doing things! Is there another equation which accounts for inequal > electrode radii? > > The really accurate method for the test I describe is not to rely on a > calculated voltage, but to hook an EHT power supply up to the (formerly) > grounded electrode, and actually measure the voltage taken to break down the > gap. However the requirement for a multi hundred kilovolt test supply means > that for most people it'd probably be easier to simply build the fiber optic > probes! > > -Dave- > > >terminals (D). When D>>R the voltage tends to be determinated by R only, > >as V=60000/R (R in cm, assuming 2 identical balls). An approximate > >expression for the voltage between 2 balls with radius R and distance D > >is: > >V=30000*R*D/(0.9*(R+D/2)), R and D in cm. > >A spark with 20 cm of length between two balls with 2 cm of radius > >corresponds to about 111 kV. > >Of course, this is for single sparks. > > > >Antonio Carlos M. de Queiroz > > > > > >

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