Re: A LUA file for BELA (a help to build electrostatic model of TC)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Finn Hammer <f-h@xxxx>

<Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>wrote:


<snip

<You don't really need to do heavy electrostatic analysis or 
differential equations to <get it right the first time!!

<snip

DC,

Your approach to Tesla Coil Design is fine for conventional disruptive coils.
I have been here 8 years now, and have gained enough experience to 
acnowledge that.
However, the electrostatic analysis i am playing with, is aimed at 
the new breed of coils.

The DRSSTC`s.

Those of us that have built this type of coil can witness to the 
fact, that flashovers from secondary to primary still is a limiting 
factor with these coils.

In an attempt to solve this problem, I have tried to add increasing 
amounts of dielectric in the space btwn. the 2 coils, only to observe 
that the problem got worse.

People who work with tightly coupled transformers for high voltage 
know it already, but I have only recently found out:
I cannot insulate my way out of a corona problem. The more dielectric 
I stuff into the gap, the more severe the corona gets in the remaining air.

The air has to be excluded all together to avoid corona in such strong fields.

I like to put the primary coil inside the secondary, but the problem 
also exsists in coils that have visible primary`s.

Pls. review this design example to understand my point of view.

I have a 200mm secondary with a voltage profile of  600kV/metre.
I want the primary coil to be inside the secondary, and I want full 
access to that coil for tapping purposes.
I already know that there is a corona problem that ruins the 
secondary coil from inside, without actually puncturing the coilform.

In the following pictures, the colour legend is set to display a 
field strength of, and beyond 3MV/m in the magenta area.
Corona will form in the red magenta area.
Of course it will happen at the top turn.
http://home5.inet.tele.dk/f-hammer/DRSSTC1.jpeg
First thing would be to introduce a grounded and slotted (slotted how 
and where remains to be determined) shield.
http://home5.inet.tele.dk/f-hammer/DRSSTC2.jpeg
Obviously, this was too simple a shield, I`l add a rounded top detail.
http://home5.inet.tele.dk/f-hammer/DRSSTC3.jpeg
That doesn`t really cut it either so I`l have to close the shield off 
at the top. Notice how it starts to resemble a cheap and readily 
available cooking utensile.
http://home5.inet.tele.dk/f-hammer/DRSSTC4.jpeg
So far so good. Now the primary is safe and sound inside it`s 
grounded shield, no need to worry about the primary getting hit by 
flashovers. But the corona problem still exists btwn. shield and 
secondary, due to the insulating substance being air. (which in it`s 
highly electrically stressed state has quit being an insulator and 
become conductive).
This is where the potting compound comes into the picture. With a 
voltage standoff ability of 50MV/m it is safe and sound in there, I`l 
just pour it in. (Yeah I know, no air bubbles, no voids, vacuum)
http://home5.inet.tele.dk/f-hammer/DRSSTC5.jpeg
But whoa! hold your horses! A new area of potentially ionized air has 
appeared outside the dielectric. Guess I have to pour some more 
potting in there:
http://home5.inet.tele.dk/f-hammer/DRSSTC6.jpeg
Ok, now it is time to stop simulating and go to the shop.

With this example I want to show a couple of things.
At first encounter, the interface of air to dielectric is counter intuitive.
At 400USD/Gallon of potting compound, it pays to be at least 
rudimentarily prepaired, before pouring.
Doing an electrostatic analysis of this problem paves the road to a 
successfull design.


There is another thing. I am a tool maker and a podiatrist. Many 
times I wish I was an EE, but I`m not. I would so much like to join 
the discussion based on knowledge.
So I study. Seek out tasks that need both manual skill and 
theoretical knowledge to complete with success.
For a period, it has been my ambition to build a tightly coupled 
resonator pair with an internal primary, so far this analysis seems 
to have brought me closest ot the fulfilment of that goal.

Cheers, Finn Hammer