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



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



Has anyone tried purposefully reducing the coupling to see the results? I'm not sure why you need the increase the coupling so much more than for classic TCs. Some experiments along these lines might produce interesting results.

Dr. Resonance



<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