Re: neon vs. potential transformer

From: 	Rodney Davies[SMTP:rgd872-at-anu.edu.au]
Sent: 	Thursday, July 17, 1997 8:01 PM
To: 	Tesla List
Subject: 	Re: neon vs. potential transformer

Hi John and Peter,

On Tue, 15 Jul 1997, Tesla List wrote:

> From: 	FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
> Sent: 	Tuesday, July 15, 1997 4:14 AM
> To: 	tesla-at-pupman-dot-com
> Subject: 	Re: neon vs. potential transformer
> In a message dated 97-07-15 01:36:44 EDT, you write:
> Yes, normal neon transformers can draw double or more their rated
> wattage, it all depends on the size of the tank capacitor.  Certain 
> capacitance values will result in an equal but opposite reactance 
> to the leakage reactance of the transformer.  The result is that a 
> 60 Hz low frequency resonant condition is created.  Effectively,
> the current limiting feature of the transformer is "neutralized", 
> allowing the transformer to draw more current.  The use of this
> "resonant charging" effect is one of the secrets of neon TC
> performance.
> I forget the formula for calculating the proper capacitor size offhand, 
> but someone will probably post it again.   A .007uF capacitor works
> well with a 12kV, 30ma trans, and a .014uF works well with a 15kV,
> 60 ma trans.

 C = ------------

 Where C is capacitance if Farads
       Pi = 3.14159....
       F is line frequency 50/60Hz
       R is impedance of transformer (Volts/Amps)
> A potential transformer is a type of transformer used by the electric
> ulitility companies for measuring the voltage on their high voltage 
> power lines.  These transformers are very well made, very robust,
> and have low losses.  Two of these transformers used together can
> approach the performance of a pole or distribution transformer.
> Unfortunately, they can be hard to obtain.

If you like Peter, you can use my SWER...
> I use a special "series-rotary" synchronous spark gap on my TCs,
> which might just help their performance a little.  I suspect however
> that a well made, multiple static gap with air or vacuum quench may
> equal or come close to the sync-gap in performance, but I can't be
> sure about that.  There's been a lot of postings on the list cautioning
> coilers not to open up their gaps too wide to prevent transformer 
> destruction.  To obtain maximum spark output however, it is necessary
> to use a maximum gap setting.  I have not destroyed any neon 
> transformers since I've been using safety gaps, but still, the possibility
> of destruction is there.

if you're going to use a rotary, it is highly advisable that it *is* a
synchronous rotary (Peter, for us it's 1500 rpm, or multiples of that..)
Asynchronous gaps + neon transformers (eventually) = dead neons.
I built a series air-quenched gap for my Neice's coil in Brisbane and
works quite well... 
Jason Judd and myself were playing with his coil this evening using a
static 7-point gap (self-quenched) and were getting a good 19-20 inches
from 2 15KV 30mA neons in parallel.
The coil is a 13.5" winding length on a 4" (I think) diam pvc pipe using
0.25mm space wound copper wire. Roughly 550 turns.
We built a rolled capacitor for it tonight which measured around 12.73 -
12.79nF. This is the best performance to date... mind you, it's was about
midnight and -3 degrees C in his garage, so we left early...

> I also like to use more than the usual number of turns in both the
> primary and secondary coils.  I use from 25 to 35 turns in the primary
> and about 1500 turns in the secondary.  But many coilers have 
> obtained very good results using far fewer turns, so I can't say for
> sure how important this is either.  In general, it would seem that more
> turns would raise the surge impedance of the tank, and lower the 
> percentage of power lost in the spark gap.

Exactly the theory Jason and I came up with. Those winding dimensions are
typically unusual, however, the idea of not loosing energy across the
spark gap was what sparked of an interesting thought pattern. I must
commend you John on your output with this type of coil...very impressive!

> It is important to use the correct sized toroid.  A toroid that is too
> small will produce numerous simultaneous spark streamers but they
> will all be short.  A toroid that is too large will not allow the spark to 
> reach it's full length.

True. We're top-loading the secondary with a spherical shaped dome about
14" in diameter.... sometimes it appears that the top capacitance is too
high, then other times it seems the other way around... We're looking at
going to a toroid probably this weekend...