[Prev][Next][Index][Thread]
Re: Toroid Size?
At 11:25 PM 1/7/97 -0700, you wrote:
>> Subject: Toroid Size?
>
>Subscriber: bert.hickman-at-aquila-dot-com Tue Jan 7 22:31:57 1997
>Date: Tue, 07 Jan 1997 10:03:46 -0800
>From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Toroid Size?
>
>Tesla List wrote:
>>
>> Subscriber: rwstephens-at-headwaters-dot-com Mon Jan 6 22:25:48 1997
>> Date: Mon, 6 Jan 1997 20:07:27 -0500
>> From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
>> To: tesla-at-pupman-dot-com
>> Subject: Toroid Size?
>>
>> All, and Chuck Curran,
>>
><SNIP>
>
>> Before I took a chance and spent (possibly wasted) big bucks on a custom made
>> piece of 14 inch diameter stainless air duct I took my considerably
larger topload
>> from my largest LTC system which is 15.5 inch cross section by 67 inch O.D.
>> and placed it atop MTC the other evening for experimental testing. I was
luckily
>> just able to retune MTC's primary at the very end of the last turn
available to
>> accomodate the full 15 kHz lower Fo that this bigger topload made my 50 mH
>> secondary now operate at. Operating happily before at 78 kHz it was
>> about to try to do something for the first time at 75 kHz.
>>
>> Low power testing with a bleeder point on the toroid confirmed tune.
>> At about 7-8 kVA, the very first time I applied power without a
>> test/bleeder point on the toroid, I was pleased to note that my
>> system could indeed _punch out_ from a 15.5 inch diameter smooth
>> terminal. The ~11 foot arc that hit the earth was noticeably hotter and more
>> brilliantly white than those I am accustomed to from this coil. After
>> about only one full second, perhaps less (it all happened so fast) of
appetite
>> wetting fun, the secondary started to break down all over itself with
interturn as
>> well as full length coil surface arcs. There was much interturn arcing
in the top
>> 40% of the secondary. I immediately shut the system down each time
>> this unwanted secondary arcing occured and would investigate the
>> damage to the secondary. I tried reducing K by raising the secondary
>> as much as 3/4 inch higher relative to the flat spiral primary than I
>> used to run safely. The old coupling was recently and successfully
>> increased to K=0.22.
>>
>> I must have lowered K to around 0.1(?) but my helper was in a hurry to
>> leave and an actual K measurement was not therefore possible. At any rate,
>> this reduction in K did not help at all. I also attempted running
>> with the toroid at several different heights above the secondary top
>> winding, and also introduced an extra 3 inch by 18 inch smooth
>> commercial toroid immediately adjacent to the top winding, placed
>> a foot or so below the big donut for extra field control. all to no
helpful effect.
>>
>> I'm going to guess that the assumed significantly higher breakout
>> voltage that the bigger topload created, plain and simply
>> OVERVOLTAGED MY SECONDARY COIL.
>>
>
>Sorry to hear about your flashover problems, Robert! From the sounds of
>it, I'd agree with your assessment that you're overvoltaging the
>secondary. The giveaway is the inability to rectify the problem by
>reducing k. With the higher breakout voltage from the bigger top-load,
>decreasing k doesn't markedly reduce the peak secondary voltage, just
>increases the number of RF cycles to get there once the gap fires. It
>could also be that the thicker, and lossier, PVC insulation is
>contributing to lower voltage withstand capability versus a similarly
>wound secondary wound with double-insulated magnet wire (like Chuck's).
>Also, a smooth conformal overcoat should significantly help "smooth out"
>the E-field, further reducing corona and inter-turn arcing.
>
>> I sure wish I had my HV probe built now so I could investigate this finding
>> meaningfully through actual voltage measurement, however, I expect
>> to be able to do so within several months.
>>
>> I was interested to note the evident violence of the damage caused
>> by the interturn coil sparks. In the past I have observed a brown
>> spot on the white PVC insulation of the #18 GA. secondary wire
>> wherever interturn arcs occurred. I had stabilized my design where
>> interturn arcing NEVER occured. This time (dinking with perfection)
there were
>> several clean craters, with no browning of the surrounding PVC, where a
hole had
>> been literally blown out of the sidewall insulation on the wire, and
clean tinned
>> copper wire was exposed!
>>
>> I think this is pretty clear evidence of massive pulse currents
>> created by the bigger topload C. I don't know what the self C of
>> this secondary is, but it plus the large topload worked out to close
>> to 100 pF! Greg Leigh's large system employed a toroid of very nearly
>> identical dimentions for which he has posted a determined breakaway
>> voltage of approximately 500 kV. That voltage stored in 100 pF
>> represents an impressive 12.5 Joules. Discharged in a half sinewave
period at
>> 75 kHz (6.65 mSec, but undercalculating the real power by calculating as
a square
>> wave) nets 1.88 megawatts of peak pulse power. Can you imagine what a
>> pinpoint of PVC insulation might do when assaulted by that much pulse
>> energy?!
>>
>
>Yeah... just think if one hit you! O =:^O
>
>> So what does one do if they find they have built a beautiful topload
>> toroid that causes such coil breakdown? The only solution I think
>> is to wind a bigger secondary to stuff underneath!!!!!!
>
>Obviously! You also need more power, more power... its
>"gotta'-get-a-pole-pig" time!! :^)
>
Huge Snip!
I found out today the local power company will give you almost anything if
you ask the right person, I was on my way home and found some guys working
on a pole and asked for insulators and ground wire, they said sure, here. I
now have a nice ground system for my coil. About the Pigs, that is also not
going to be a problem talking to the right person. A croaker will go a long
way in the bosses pocket. Another hint.
********************************************
* T E S L A C O I L S *
********************************************
Kevin Nardelle knardell-at-accesscom-dot-net
My main web page soon to be all TESLA
related with lotsa pictures and links.
http://www.accesscom-dot-net/nardell
Non related sites I have
The Louisiana Swamps Online (Under construction)
http://www.icorp-dot-net/users/kev
***********************************************
Get me on CuSeeMe for live video and chat!
Shop talk, Show and tell, Ect...
The Continuum Reflector-High speed and Color
204.107.221.9 Conf. ID 2601
***********************************************