[TCML] Test of Saturable Reactor in my 200bps SRSG Medium Teslacoil

["Teslalabor" <teslalabor@xxxxxxxxxxx>]

Hello List,

I want to start a discussion about the possibility of using a saturable 
reactor for current limiting - especially in a system based on a synchronous 
rotary spark gap. The idea of using a saturable reactor for current limiting 
is not new I know, but I think very less information about this is 
available.

My particular goal is, to do the current-limiting of my big coil (runs up to 
30kW input power) with 2 heavy saturable reactors.
After getting suitable reactors and also the help of a very friendly 
listmember getting the beasts running, I now start some tests with one of my 
reactors in combination with my medium sized teslacoil, I have postet about 
this TC several times in the last weeks. In combination with a dummy load, 
this TC is an optimal device for performing some nice tests.

First of all, I made a video which shows the test-setup:

http://www.youtube.com/watch?v=JBNglLIUpRE

In the test, I have replaced the original air - gapped ballast inductor 
(which I have well built) by the saturable reactor. The original inductor is 
set to the inductance value of 31mH, which I got out of Richie's Resonant 
charging design procedure. Now we all know, that the inductance of 31mH of 
such an air gap-inductor REMAINS NEARLY CONSTANT when different voltages are 
applied. It doesn't matter, if 20Volts, 100Volts or 240Volts are applied - 
every time this thing has 31mH.
Now let's have a look at the saturable reactor, which shows a completely 
different behaviour, I did the following test to check its properties:

I applied a DC-controlcurrent of 20 Ampere to the reactor's controlwindings 
and made a measurement of different voltages and the current flowing and 
calculated the inductances. As you can see in the following table, the 
inductance is not constant as it would be in an air gapped inductor. The 
inductance changes with the applied voltage:

Voltage in Volt  Current in Ampere Inductance in mH

20                       3,65                           17,44
40                       6,50                           19,59
60                       9,18                           20,80
80                       11,63                         21,90
100                     13,87                         22,95
120                       15,92                       23,99
140                       17,62                       25,29
160                       19,20                       26,53
180                       20,47                       27,99
200                       21,50                       29,61
220                       22,48                       31,15
240                       23,33                       32,75

This change in inductance is because there is no air gap in the core I think 
(correct me if I am wrong). Okay now have a look at the second video showing 
the test I performed at the reduced voltage of 150V:

http://www.youtube.com/watch?v=XZn4bZOKS4U

I set the DC - control current so, that the saturable reactor has the 
inductance of 31mH @ 150V - the same inductance, the original air gapped 
inductor has. See, how I adjust the voltage to 150V and everything runs 
quiet smooth. NO CHANGES in the timing of the SRSG were made! But there is 
one curious thing which I do not understand: When changing the inductance of 
the saturable reactor, the inductance on the high voltage side of the 
feeding transformers of the TC also changes, because it is reflected by the 
turns-ratio squared. And so, I EXPECTED an extremely change of the timing or 
even firings of the safety gap, when changing the inductance only slightly - 
but as you can see in the video, is seems to be not affected?


Best Regards,
Stefan 

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