Re: [TCML] Magnetic saturation

[David Speck <Dave@xxxxxxxxxxxxxxxx>]

JF,

I have used a saturable reactor (SR) with good results to limit the 
current draw of my potential transformer in a SGTC.  A very small DC 
control voltage applied to the control windings of the reactor can 
produce large changes in the current allowed to pass through the primary 
winding of the saturable reactor.

In my experience, saturable reactors are way too slow to be used in 
place of the spark gap in a disruptive coil.  I've noted that when I 
turn off the control signal to my SR, the coil actually takes something 
like half a second to stop discharging.  I have no filter cap on the DC 
control circuit to the SR, so there must be some intrinsic property of 
the SR that keeps it  from turning off instantly.

The operating parameters of a SR and a spark gap are totally different.  
A spark gap goes from a near perfect insulator to being a pretty very 
good very high current (hundreds or thousands of amps), low loss 
conductor in a fraction of a millisecond or thereabouts.  A SR would 
have to be huge to handle the sorts of currents involved in a TC tank 
circuit, and even then, the inductance of the SR core would be a huge 
drain on the power of the circuit.  The only significant inductor you 
want in the tank circuit is the TC primary coil.  SRs are just not the 
right tool for the job.

Not sure how a gyrator would help in a TC circuit.

Solid state thyristors (SCRs, or TRIACs) in general are too slow to be 
effective on a TC tank circuit, a pity, 'cause there are a lot of them 
available.  They are also very poor at handling reverse currents that a 
spark gap doesn't care about.  When the gap in a TC tank circuit fires, 
the high voltage in the cap might start out at (+) voltage, but it 
rapidly drops through zero to nearly the same voltage in the opposite 
(-) polarity.  This damped ringing waveform oscillating about the zero 
voltage point is what makes a TC work. Some have successfully small 
built TCs using specialized hydrogen vacuum tube thyratrons, but most 
thyratron tubes are poorly suited to this duty, as they have poor 
reverse voltage operating characteristics.

HTH,

Dave

On 9/1/2012 3:01 PM, vatercox@xxxxxxx wrote:
> Dear List,
> I'd like to hear some opinions on "magnetic saturation" only it does seem similar in some ways to dielectric breakdown  even if only  in that it is voltage related phenomena.
>
> Has anyone used a saturating reactor in place of a spark gap? Is it possible?
>
> What actually happens when the inductor saturates? Doos the voltage across the inductor continue to rise albeit at a slower rate like a zener diode  or does it even fall, analogous to negative resistance of an avalanching spark gap or a neon lamp?
>
> and while we are talking about it what about ther case of a gyrator- a circuit using a capacitor and an active element that mimics th behavior of an inductor.  how about using a a thyristor as the active element to simulate saturation?
>
> JF Cox

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