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Registered Member #1450
Joined: Sun Apr 20 2008, 09:59PM
Location:
Posts: 10
Hello mateys, not been here for ages and it's even better then last time! keep it up.
I was wondering, apart from SCRs and their like, what mechanisms are avaliable for switching high-impulse HV circuits? I was thinking in terms of a pneumatic cylinder and a custom made contactor to close very fast and resist opening under the force created by a rapidly rising current. I do like the idea of a pneumatic actuator, especially since I can operate the thing in question with a rubber pipe as opposed to a wire... we like isolation. Some ideas would be great.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Gas discharge switches are often used in pulsed power applications e.g. spark gaps, pre-ionized spark gaps, triggered spark gaps, pseudo-spark switches, thyratrons, triggertrons, krytrons, sprytrons, and so on.
There is the ignitron, basically a mercury vapour recitifier with an igniter electrode that triggers a discharge between a graphite electrode and a puddle of mercury.
Then there are one-shot dielectric puncture solid state devices, which can be made to switch phenomenal currents and voltages in very costly experiments.
If something a bit slower and smaller is acceptable, vacuum relays can come in handy. These are basically an electromagentic relay with the change-over contacts in a sealed glass chamber like a valve [US: tube]. Small ones capable of switching 5 or 10kV quite often appear second-hand on ebay.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Tinfoil_Cat wrote ...
Interesting, thanks - I'm intregued by the triggered spark gaps, just trying to figure out how the devil they work.
Presumably in terms of current rise time and maximum available peak power mechanical switches don't really cut it?
The simplest type of triggered gap has three electrodes - the two electrodes of the basic gap, but with a third one between them. The air gap between the main terminal electrodes is sufficient to hold off breakdown, until a trigger voltage is applied to the centre electrode. This sparks over to one of the main terminals, effectively shortening the main gap, which then sparks over. There are all sorts of variations of this - having the electrode a bit off to one side, and so on - but that's the basic principle. Specialised triggered gaps containing high pressure hydrogen, or deuterium, are sometimes called trigatrons.
As for your second question, the choice of a switch in any circuit is always made on the basis of the application. Decide what it is the switch must do, how much current it must handle, how much voltage it must hold off, how fast it must do its job for your purpose, and how many times it must do it before probable failure, and then look at the easiest and cheapest way of attaining those ends.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
I think a pneumatically operated switch would be excellent, if you ensure that the contacts never actually touch then they can't weld together, and you effectively have a triggerable spark gap, rather than applying an initiating arc you would be shortening the gap.
Look at web pages and discussions here , especially high energy discharge systems such as rail guns and coin-shrinkers.
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High speed switching
