Re: [TCML] Spark gaps (again)

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

Yeah,but the dynamic "resistance" of the gap isn't only the function of current.
Beside other things,it's the function of time.That was my point.

DD. 
--- bert.hickman@xxxxxxxxxx wrote:

From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Cc:
Subject: Re: [TCML] Spark gaps (again)
Date: Sat, 07 Mar 2009 00:42:45 -0600

Hi Dex,

It's a bit more complex than this, since the dynamic "resistance" of a 
firing spark gap is a function of current flow. With RF arcs, the higher 
the peak current, the lower the average arc "resistance". It's been 
found experimentally that a firing gap actually behaves much like a 
bidirectional Zener diode that has a typical voltage drop in the range 
of 100-200 volts. This is relatively constant for a given gap spacing 
and electrode system.

Stacking a series of identical gap increases gap conduction losses 
proportionally, since instantaneous power loss is the primary current 
times the (increasing) sum of gap voltage drops. However, smaller gaps 
lose heat more quickly through axial heat transfer from the plasma 
channel to the electrodes, especially when electrodes are made from 
nonrefractory metals with excellent thermal conductivity such as copper. 
The close proximity of cool electrodes quickly removes heat from the 
gaps, allowing them to recover their dielectric strength more quickly 
after a current zero.

By using gases with low molecular mass (such as hydrogen), many small 
gaps, and massive copper electrodes, the result is a "quenching gap". 
This technique was well known back in the days of spark radio. It can 
achieve first notch quenching, generating a clean ringup, quench, and 
extended secondary ringing decay, but this is at the expense of 
comparatively high gap losses.

Bert


Dex Dexter wrote:
> The thing are the resistances of gap arc columns.
> They are not the same I think becouse the impulse arc has the expansive evolution.
> How much they  differ I don't know :( 
> Any proof for that?
> 
> Dex  
> 
> --- jimlux@xxxxxxxxxxxxx wrote:
> 
> From: jimlux <jimlux@xxxxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Cc:
> Subject: Re: [TCML] Spark gaps (again)
> Date: Thu, 05 Mar 2009 20:30:25 -0800
> 
> Dex Dexter wrote:
>> I guess the 'arc column' voltage drop must be considerably higher in
>> a pulsed transient arc lasting for 10-20 microseconds than in a
>> steady state arc of the same lenght and current.How much higher I
>> don't know.Catode drops should be the same in both cases.Yes/No?
> 
> Cathode drop would be the same.
> The arc column heats up in microseconds (viz camera flash), so I don't 
> know that TC arcs are all that different than a free-burning arc.
> 
> 



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