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Re: [TCML] Magnetic saturation



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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