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Re: Blumlien HV generators

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Robert,

See comments below:

Original poster: robert heidlebaugh <rheidlebaugh@xxxxxxxxxxxxxx>

Gerry  Removing the shield dose nor solve the problem it abaits the problem
by removing the capacitance.

I agree that removing the shield doesnt solve the problem (assuming it is what I think it is)

They are slower than the speed of light by 12% or more.

The velocity constant in say RG8U is about .7 or 1.5ns per foot. Removing the shield will introduce air as part of the dialectric and improve the prop velocity closer to the speed of light.


When you send a pulse down a coax cable the same thing happens.

Yes for a completely unterminated coax the voltage pulse traveling down the coax will double at the open end. If the coax is open at one end and shorted (SG firing) at the other end. There will be no damping (assuming lossless coax) and the pulse will be propagating up and down the coax indefinitely between reflection coefficients of +1 (at open end) and -1 (at shorted end) with the polarity inverting every time the pulse travels to one end and returns. There will a resonance at a frequency corresponding to four travel times (down and back twice). If some energy source (at the right frequency) addes energy to the coax, the voltage will grow perhaps uncontrollably.

The problem comes into play when you consider
the cable's impedance is 50 ohms. If you try to match that you put a 50 0hm
short across your 10 Kv 30 ma transformer and nothing works other than you
smoke test your NST.

If you put 50 ohms to ground at the NST end, yes nothing will work, and NO you wont smoke the NST - it's current limited. If you put a capacitor in series with the 50 ohms and the C is chosen so its impedance is insignificant at the frequencies resonating with the coax length and is high impedance at the 60 Hz charging frequency, then the charging waveform will not be affected and yet the coax will be terminated at the frequencies of interest.


By using the coax core with no shield the capacitance
is gone so the impedance is as high as is your transformer.

No. The capacitance is reduced but not gone. The capacitance remainding on the unshielded coax is to earth and is still distributed. The inductance of the line has been increased somewhat and is also distributed. The wave equation still applies and you still have a traveling wave. The impedance of the line gets higher (maybe close to the impedance of free space). The impedance of the transformer will depend on the transformer. For a 5KV PIG, the impedance is 41 Kohms and there are of course HF parasitics. What I believe has been accomplished is a change in resonance of the cable to where maybe the exitation frequency is out of band.

If one wanted to experiment, one could take a setup with shielded coax that did exhibit the problem and then remove the shield to see the problem go away and then increase the length of unshielded coax so the prop times are the same as with the shielded coax and see the problem reoccur. The problem might also reappear if the cable is rerouted to increase the capacitive loading on the cable or the exitation frequency is somehow changed. An unshielded cable does not have a very well controlled environment, but probably works for a given setup. The real question is what is the safety margin.

Gerry R.


> From: "Tesla list" <tesla@xxxxxxxxxx>
> Date: Mon, 07 Nov 2005 16:59:05 -0700
> To: tesla@xxxxxxxxxx
> Subject: Re: Blumlien HV generators
> Resent-From: tesla@xxxxxxxxxx
> Resent-Date: Mon,  7 Nov 2005 16:59:46 -0700 (MST)
>
> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Dr R,
>
> Is the effect one of two I mention below?? or is it a third
> mechanism??  If it is a transmission line effect, can you explain why
> removing the shield fixes it and why proper termination
> doesn't???  If a resonant charging effect, can you descibe the L that
> the coax capacitance is resonanting with, the resonant frequency, and
> how this works???   If a third mechanism, I would like to challange
> you for the benefit of all the readers here to give a quick synopsis
> of this effect :o)).
>
> Knowledge is everything and sharing it is golden.
> Gerry R.
>
>
>
> Also is it
>> Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
>>
>> These effects are well documented in Sargent & Dolan's book -- Power
>> Electronics.  Also covered are both strip line and circular HV
>> generators. Very novel designs.  It's out of print but I believe
>> that Bert Pool (Stoneridge Engineering) has some copies for sale.
>>
>>> Anyway, going to the intent of the original post,  I'm trying to
>>> understand the mechanism of voltage growth when using a shielded
>>> coax (not because I want to use shielded coaxes, but because I want
>>> to understand). Is the phenominum transmission line effects being
>>> underdamped while energy is feeding the line,  is it a resonant
>>> charging effect (series LC) due to the capacitance of the coax, or
>>> is it some other mechanism???  Also in the TC context, is the
>>> blumlein effect the same as the transmission line effect I
>>> described above or something else???
>
>
>
>