RE: Streamer Voltage

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

Original poster: "John H. Couture by way of Terry Fritz <teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


In the Tesla Coil Construction Guide there is a graph that shows Secondary
Voltage vs Spark Length for classical Tesla coils. This graph has proven for
several years to be reasonably accurate when the spark is a controlled
spark. For example for an 18 inch controlled spark the voltage would be
about 500 Kvolts.

It should be noticed that using input wattage to find the spark length does
not work. It is a well known fact that every TC has a maximum input wattage
where increasing the wattage does not increase the spark length. In other
words when increasing the input wattage to the TC a point is reached where
the increment of input wattage equals the increment of loss and the spark
length does not increase.

It is obvious that the TC Secondary Voltage is a function of the design and
other TC variables. Because of these limitations any TC secondary voltage
equation would have to be for only a certain TC design and size. The graph
in the TCC Guide was originally made for a computer program that also
recommended a design and size of classical Tesla coil when a certain
secondary voltage was desired.

John Couture

--------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, May 07, 2003 8:09 PM
To: tesla-at-pupman-dot-com
Subject: Re: Streamer Voltage


Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi David,

At 12:08 AM 5/7/2003 -0500, you wrote:
 >Hi All,
 >
 >This has been bugging me for a while. Is the streamer voltage measured by
 >the combination of topload geometry plus streamer length, or just by
 >streamer length?

Streamer length is more a function of power as shown in John Freau's
streamer length formula:

L = 1.8 x SQRT(input power)

Since streamers grow on stands of already established hot ionized
air,  Relatively low voltages can reach out a considerable distance.

 >With my 4" coils, the 6" sphere had a breakdown voltage of 571KV by
 >Sd=((MV/7.5)*2)*100.  Sd=sphere dia in cm.  MV= voltage in megavolts.

The radius of a 6 inch diameter sphere is 3 inches or 0.0762 meter.  For
3MV/m, that gives a voltage of ~229kV to break out.

 >It's 18" streamer would come to 502.92KV at 1.1KV/mm.  If the two add
 >together it would make the total voltage 1MV+.  If it were just streamer
 >length the 502KV would not even produce corona on the sphere.


A pretty good guess for maximum top voltage is:

Vt = 0.7 x SQRT( Cp / Cs) * Vfire


 >Or could it be that, the voltage peaks enough to produce corona, and then
 >drops, as the streamer is formed.

Yes. It is very likely that a high initial voltage gets loaded down by the
increasing size of the streamer.

Cheers,

          Terry
 >
 >David E Weiss