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Re: oil filled resonators

>>From MALCOLM-at-directorate.wnp.ac.nzMon Oct 14 21:28:58 1996
>Date: Tue, 15 Oct 1996 09:50:59 +1200
>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>To: tesla-at-pupman-dot-com
>Subject: Re: oil filled resonators

>Hi Robert, all,
>
>> I'm in the process of building a large vacuum tube driven TC for a
>> commercial client right now.  Last year I fabricated an oil filled
>> resonator for this project consisting of a 16 inch diameter
>> fiberglass form close wound with #8 AWG thermaleze copper wire to
>> a length of 5 feet. This coil is positioned coaxially inside a 200
>> US gal steel cylindrical drum and filled with VoltEsso 35 oil.  A
>> large oil filled shedded ceramic bushing (12 inch outside diameter
>> and 30 inches long, 8 inch oil filled hollow around a 1/2 inch
>> copper waterpipe HV buss inside) sticks vertically out the top side
>> of the horizontal drum at one end making it look like the
>> smokestack on a steam locomotive.  A spun aluminum terminal tops
>> the bushing as the HV output.  Inside at the other end is a 15 turn
>> flat copper ribbon spiral primary.  I have little test time on
>> this device as yet, and only with a modest vacuum tube exciter
>> oscillator.  I am not generally pleased so far with the Q which is
>> lower than from a similar coil in air and without metal walls
>> around.  Note also that the surrounding metal container is lossy
>> mild steel, not silvered copper.  There should be both eddy
>> current as well as I2R losses in the skin depth.  Operating
>> frequency is 100 kHz. 
>
>I'd be inclined to try a non-conductive container if poss. If wall
>conductivity is anywhere between perfect and zero, it will lose a
>lot of energy. Be interesting to work out the wall impedance where
>this reaches a maximum. Also, you'll end up with a lot more 
>distributed C than is desirable. The Q of Abramyan's container-
>enclosed accelerator was rather poor (about 70 from memory) despite 
>silvered walls. The other thing is that the primary is going to
>have an uphill battle due to interference from the more-or-less
>shorted turn surrounding it. Also, have you thought about using much 
>higher k's since the coil is oil-immersed?
>    Could someone please post on what plastics are resistant to attack 
>from commonly used oils?

>Malcolm

Malcolm,

I made the decision to enclose the entire two coil resonator within a 
steel drum to satisfy the client's neeed to have a Tesla coil 
resonator that would be as immune as possible from room placement, in 
or out side of a fully shielded test room.  

Prior to filling with oil I set the position of the primary coil to 
the secondary with a 3 kW vacuum tube oscillator and simply set the K 
factor for maximum resonant voltage rise against the required 100 pF load 
capacitance.  I really have no way of knowing if this K factor is 
better or worse with the oil now introduced until I undertake the 
next series of tests.

A non-metalic drum as you suggest would not have provided the 
shielding required, but I'll bet would make a normal air insulated 
coil system capable of much more fire.  The ultimate problem then becomes 
where you are finally obliged to exit the oil filled containment with 
your high voltage leads into surrounding air.  

Regards,
rwstephens