Coaxial magnetically-quenched spark gap?
J. Aaron Holmes, Wed Aug 02 2006, 08:48PMThis may have been discussed before, but all I can find talks about using actual magnets, and it appears as though nobody has actually tried it.
In any event: I recently picked up a used copy of "Transmission and Distribution Electrical Engineering", a heavy read even for a EE (I'm guessing), but almost impenetrable for me!!
One rather interesting chapter deals with arc quenching in circuit breakers, and one method described involves coaxial electrodes, where one electrode is a central bar, and the other is (effectively from what I can tell) the inner turn of a field coil assembly surrounding the bar. Thus, when an arc occurs, the arc current passes through the field coil and generates a magnetic field which causes the arc to spiral rapidly around the central bar electrode. The spiraling action stretches the arc until it "snaps".It would be interesting to try this as a spark gap, I think, though it would seemingly involve adding inductance to the primary circuit (unless somehow you could use the primary winding itself as the field coil, placing your spark gap right in the middle underneath your secondary...hmmm...). A small fan would seem to have a much easier time of blowing out the spark, too, if it was magnetically stretched out at the same time.
Might be interesting to try on a small coil or just with cap discharge: Use two short lengths of copper tubing nested inside each other as your gap electrodes, then wrap the lead connecting to the outer tube around that tube a few times. Would that work?
Regards,
Aaron, N7OE
Re: Coaxial magnetically-quenched spark gap?
dan, Wed Aug 02 2006, 09:15PM
You don't really want to quench too quickly or too late. You want to quench only at a primary notch, after all the energy has be transferred to the secondary side. (and thus voltage is nil across the gap.) If you quench too soon or too late you wouldn't be getting maximum energy transfer. It seems with this method quench times would either not change or would be rather unreliable. The main problem with gap quenching is that if super hot ions are left behind after a primary notch the gap can reignite when the secondary tries to push energy back into the primary. Thus a SRSG, ARSP or a high power fan if its a static gap are used to prevent that.
dan, Wed Aug 02 2006, 09:15PM
You don't really want to quench too quickly or too late. You want to quench only at a primary notch, after all the energy has be transferred to the secondary side. (and thus voltage is nil across the gap.) If you quench too soon or too late you wouldn't be getting maximum energy transfer. It seems with this method quench times would either not change or would be rather unreliable. The main problem with gap quenching is that if super hot ions are left behind after a primary notch the gap can reignite when the secondary tries to push energy back into the primary. Thus a SRSG, ARSP or a high power fan if its a static gap are used to prevent that.
Re: Coaxial magnetically-quenched spark gap?
J. Aaron Holmes, Wed Aug 02 2006, 09:38PM
You can always put a variac on your blower to make sure your air-blast gap doesn't blow stuff out too quickly. That's always worked well for me, at least.
As for the magnetic aspect, you might regard it similarly. I mean, perhaps you tap in or out on your field coil for the best quench. That, or you put the field coil assembly somewhere above or below the coaxial electrodes, and vary its proximity to adjust quench, kind of like raising or lowering your secondary to vary coupling. Seems like it would work.
J. Aaron Holmes, Wed Aug 02 2006, 09:38PM
You can always put a variac on your blower to make sure your air-blast gap doesn't blow stuff out too quickly. That's always worked well for me, at least.
As for the magnetic aspect, you might regard it similarly. I mean, perhaps you tap in or out on your field coil for the best quench. That, or you put the field coil assembly somewhere above or below the coaxial electrodes, and vary its proximity to adjust quench, kind of like raising or lowering your secondary to vary coupling. Seems like it would work.
Re: Coaxial magnetically-quenched spark gap?
Terry Fritz, Thu Aug 03 2006, 07:02AM
Hi,
The big problem with Magnetic Quench in the past is that folks tried to use the primary current for the electromagnet. But just when you want to quench, the primary current goes to "zero"... When all the energy is in the secondary side, the primary ain't got no current...
But fixed or externally powered magnets should do far better.
Cheers,
Terry
Terry Fritz, Thu Aug 03 2006, 07:02AM
Hi,
The big problem with Magnetic Quench in the past is that folks tried to use the primary current for the electromagnet. But just when you want to quench, the primary current goes to "zero"... When all the energy is in the secondary side, the primary ain't got no current...
But fixed or externally powered magnets should do far better.
Cheers,
Terry
Re: Coaxial magnetically-quenched spark gap?
Dr. Shark, Thu Aug 03 2006, 10:00AM
Not so sure... I a TC, you want to dissipate as little energy as possible in the spark gap, so the idea is to keep the arc as short as possible. Streching the arc in any way would probably decrease the primary Q by a great amount. I am not an expert on SGTCs though.
I have come across a similar concept in a high current switch for a railgun or so. Aparently the traveling spark causes less wear on the electrodes, and it extinguishes very rapidly once the B-field has blown the arc away from the electrodes.
Dr. Shark, Thu Aug 03 2006, 10:00AM
Not so sure... I a TC, you want to dissipate as little energy as possible in the spark gap, so the idea is to keep the arc as short as possible. Streching the arc in any way would probably decrease the primary Q by a great amount. I am not an expert on SGTCs though.
I have come across a similar concept in a high current switch for a railgun or so. Aparently the traveling spark causes less wear on the electrodes, and it extinguishes very rapidly once the B-field has blown the arc away from the electrodes.
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