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Re: [TCML] Tesla's topload
Shannon
Here is the modern equivalent of Tesla's "segmented electrode"
system for making very (VERY) large electrode systems.
http://www.phenixtech.com/files/admin/facilities52010.pdf
Phenix Technologies are a leading USA manufacturer of high voltage,
high power test equipment, for the power and R&D industries.
Regards
On Fri, Apr 8, 2011 at 7:36 PM, Weinhold Shannon L
<Shannon.L.Weinhold@xxxxxxxxxxxxxxx> wrote:
> Ok, so after a careful analysis of Tesla's patent #1,119,732, I think
> I've determined the true reason for Tesla's use of the half spherical
> metal plates.
> He hints around the usability of separate elements with a small radius
> of curvature that are spaced close together:
> "I employ a terminal of relatively small capacity, which I charge to as
> high a pressure as practicable. To accomplish this I have found it
> imperative to so construct the elevated conductor so that its outer
> surface, on which the electrical charge chiefly accumulates, has itself
> a large radius of curvature, or is composed of separate elements which,
> irrespective of their own radius of curvature, are arranged in close
> proximity to each other, and so, that the that the outside ideal surface
> enveloping them is of a large radius."
> And thus the small diameter ring toroid and other designs are given the
> ok.
> But he doesn't give the specific reason for using the half spheres.
> He does later though, while describing the diagram.
> He describes the 3rd coil, and then a connecting metal cylinder that
> connects the 3rd coil to the elevated terminal, and specifies that the
> diameter of that cylinder should be "of a radius much larger than that
> of the half spherical elements"
> So what I am gathering here is that the half spherical plates, even
> though they are a part of a larger outer surface, will still tend to
> have their own electrical field shape that, relative to their small
> radius of curvature, is sharper than that of the metal connecting
> cylinder, and thus a streamer is more likely to break out from them than
> it is from the cylindrical connector.
> It ties in with his desire to avoid the "inconceivable violence" that he
> mentions will take place should the points of maximum pressure be
> shifted below the elevated terminal.
>
> Although I am curious...if we are to use a toroid constructed of the
> smaller diameter rings...is the capacitance the same as a equally sized
> solid surface toroid? If so, it this only true at high voltage? He was
> really pushing the use of the smallest possible capacity and charging it
> to the maximum potential.
> Does a multi ring toroid have less capacitance but still have the same
> potential before breakout occurs?
> I'm not an expert on capacitance, but I'm assuming that the surface area
> of the electrodes, the dielectric constant of the insulating material,
> and the thickness of the dielectric determine the overall capacitance.
> Do the rules change when we're dealing with high voltage?
> I'm trying to visualize it all in my head...I'm sure you genius peeps
> out there can fill in the gaps.
> Have a great weekend all!
>
>
> Shannon Weinhold
>
> "An inexpensive instrument, not bigger than a watch, will enable its
> bearer to hear anything, on sea or land, music or song, the speech of a
> political leader, the address of an eminent man of science, or the
> sermon of an eloquent clergyman, delivered in some other place, however
> distant. In the same manner any picture, character, drawing, or print
> can be transferred from one to another place."
>
> ~Nikola Tesla - "The Future of the Wireless Art" 1908
>
> (how did he know?)
>
>
> -----Original Message-----
> From: Derek, Extreme Electronics [mailto:tesla@xxxxxxxxxxxxxxxxxxxxxxxx]
>
> Sent: Thursday, April 07, 2011 8:58 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Tesla's topload
>
> Carl,
> If we assume that corona as composed of small streamers and "The
> appearance of streamers will increase the capacitance". Then surely the
> corona will increase the capacitance. I also think that as a finite
> element toroid appears to have roughly the same capacitance as a
> similarly sized traditional one the field must account for the extra
> charge handling capacity. As I said earlier I suspect this is a small
> effect and possibly very small on a regular toroid. But on a finite
> element toroid or one designed with bumps maybe the effect is larger..
>
> I totally agree regards the breakdown voltage of a smaller radius, and I
> don't think irregular toroids will be the next great improvement in
> tesla coiling, but I'd like to prove that there was some change in
> capacitance and of what scale it was..
>
> RE: Streamer loading IIRC Steve Connor and Terry Friz did some tests a
> while ago regarding the capacitance and loading of streamers, have a
> search in the TCML archives or on 4hv for the details, Terrys rule of
> thumb for streamer loading was 220k + (1pF/foot).
>
> Cheers
> Derek
>
> On 07/04/2011 15:50, Carl Noggle wrote:
>> Hey---
>>
>> The capacitance of any object is the effect of the electric field
>> between the object and the rest of the universe. If we visualize the
>> EF of a toroid, the nature of the surface will be seen to have little
>> influence on the whole EF. A rough surface will cause the toroid to
>> light up with corona at a lower voltage, since the EF writ small at
>> any part of the toroid is what determines the breakdown voltage at
>> that point or area.
>>
>> Since the breakdoown field for air is about 25 or 30 kV/cm (depending
>> on altitude), a smooth sphere will have a breakdown voltage of 30kV
>> times the radius. A toroid will have a breakdown voltage of about
>> twice that of the sphere if the "tire" radius is the same as the
>> sphere. That is, a clean, smooth toroid with a 5cm "tire" radius will
>
>> have a breakdown voltage of 30 x 2 x 5, or 300 kV. Any small
>> imperfection will reduce the breakdown voltage, usually drastically,
>> as the local EF at the point is much higher than the EF at the smooth
>> surface of the toroid. Therefore a corona will form at that point at
>> a lower voltage. However, this effect will not change the toroid
>> capacitance.
>>
>> The appearance of streamers will increase the capacitance. The plasma
>
>> channels of these streamers probably have relative high resistivity,
>> so this adds energy dissipation in the sparks (which is why they tend
>> to rise). The advantage of this is that it lowers the Q of the
>> secondary tuned circuit, so that the tuning of the coil becomes less
>> critical. This is why TCs usually seem to work pretty well over a 10%
>
>> or 20% primary tuning range.
>>
>> Has anybody actually measured this change in Q, or does anybody know
>> the resisitivity of the spark channels? These things would be very
>> interesting to know. The sparks in the main switch gap have very low
>> resistivity, and like lightning their resistivity may be lower than
>> copper or silver, so the primary Q should be quite high.
>>
>> ---Carl
>>
>>
>>
>>
>>
>>
>>> Phil,Dave, All,
>>>
>>> My gut feeling is that the effect is quite small, especially with
>
>>> smooth top loads (spheres/toroids). Because of this, any breakout
>>> loading will overwhelm the additional field created capacitance.
>>>
>>> As it happens, the coil that I am building at the moment is a
>>> classic SSTC with a non-smooth toroid design. As it utilises base
>>> current feedback, I'm hoping that running the coil with no visible
>>> breakout, I will see a resonant frequency change as the bus voltage
>>> is increased, indicating a change in the capacitance of the top-load.
>>> This should prove or disprove the theory.
>>>
>>> Also as Tesla coils are an AC system, it would also suggest that
>>> the capacitance of the top load would vary over the period of the
>>> driving frequency, with zero crossing having minimum capacitance and
>>> peak voltage points having more. This should be seen in the shape of
>
>>> the field waveform measured in open air near the coil. A comparison
>>> to a similar sized but more conventional topload would help to
>>> eliminate any driver/coil related waveform shape irregularities.
>>>
>>> Cheers
>>> Derek
>>>
>>>
>>>
>>> On 06/04/2011 23:14, Phil Tuck wrote:
>>>> Derek, et al
>>>> If it did then people would have noticed an anomaly in the tuning
>>>> figures by now I think. We know that best performance generally
>>>> occurs when the primary is set to resonant lower than the secondary
>>>> because of the streamer loading and this normally is by an amount of
>
>>>> around 1.5pF per foot. However, if what you say were right, then
>>>> would we not have noticed additional factors at play on the bigger
>>>> coils that could not be accounted for purely by streamer loading
>>>> alone?
>>>>
>>>> Regards
>>>> Phil Tuck
>>>>
>>>> www.hvtesla.com
>>>>
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
>>>> Behalf Of Derek, Extreme Electronics
>>>> Sent: 06 April 2011 05:49
>>>> To: Tesla Coil Mailing List
>>>> Subject: Re: [TCML] Tesla's topload
>>>>
>>>> This does raise an interesting question, does the capacitance of the
>
>>>> topload increase as the voltage on the topload increases because the
>
>>>> field around the topload adds to the effective external dimensions
>>>> of the topload, so increasing capacitance ?
>>>>
>>>> Derek
>>>>
>>>>
>>>> On 06/04/2011 01:48, bartb wrote:
>>>>> I dunno, it would be interesting to model: say of sphere's with
>>>>> diameters equal to a corresponding toroid minor diameter, but with
>>>>> the spheres spaced apart so that 1/2 of the diameter of each sphere
>
>>>>> intersects the other creating large bumps of sorts. Unfortunately
>>>>> not something Javatc can do as the topload sphere's would have to
>>>>> be offset from center (not something it can do now). Possibly Paul
>>>>> or Antonio's software could do a quick and dirty comparison.
>>>>>
>>>>> Take care,
>>>>> Bart
>>>>>
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>
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--
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA
Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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