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isolated perpendicular main and trigger gaps

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LAN_403

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Fri Jul 31 2015, 10:21PM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

I am attempting to make a rather unique triggered spark gap. The method I have chosen is for learning more about the nature of high voltage interacting fields whose sources are totally isolated from each other by any physical connections (no common ground terminal, etc.) HOWEVER, there may be some ion-type induced "connections" created.
It goes something like this:

I have a high voltage capacitor (in series with some main load--of...whatever!). The capacitor is connected to the load via a high current triggered spark gap (TSG). This TSG consists of the two main high current-voltage electrodes (North-South) connected to the main firing capacitor and (optional in theory) series load. Now the trigger: This will be another pair of (East-West) trigger electrodes level with the North-South main electrodes, across which I can switch a very low-current, high trigger voltage of around 30kVDC to 40KVDC. This will be a "corona" stream. Remember, The two power supplies are completely isolated!

I would like some information on the following, for which I have searched high and low--with no luck:

1) When the corona "trigger" gap (placed relatively far from the main gaps to prevent direct arcing at maximum voltages) fires and enters the main gap's E-field, are there any significantly conductive "+"ion or electron paths that will connect the two isolated sets of electrodes in any way by means of the fields and/or charged particle currents?

2) What are the different trigger requirements to get a conductive arc across the main gap. Mainly, for example, if the main capacitor were 0.5uF, say, compared to 1000uF---these values are random and just for examples. Does the lager capacitance get more "difficult" to fire with increasing capacitance (and/or voltage)? If I know that the trigger current can go straight through the main gap with no load connected to it (...naturally), then how do different capacitive loads effect the requirements required of the trigger to "burst" through the "stiff", "loaded" main gap electrodes? Am I wrong in assuming that a 'stiff' main gap electrode potential (due mainly to high capacitance?) is much harder to fire than a lower capacitance, (or voltage) load?

Antonio

Sat Aug 01 2015, 01:17AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Some opinions, not necessarily backed by testing:
The trigger will work too from generated ultraviolet light, so it's not a great problem to place the trigger electrodes in a way that avoids the main discharge touching them.
More capacitance across the gap turns the discharge easier, because there is more charge available to form the spark channel. After a certain value of capacitance, quite low, there is no more difference, however.

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Sat Aug 01 2015, 06:19AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Thanks Antonio,
I'm sure for the UV trigger you are speaking of a much shorter wavelength than the common 405nm.

I was under the impression that a larger charged capacitor would be harder to trigger-discharge--thanks for that fix.

I will have plenty of capacitance charge, so once triggered, I am assuming the main gap will keep conducting until everything has (extremely rapidly) run down.

I am thinking about one of those ion ray gun circuits, as the trigger electrodes, fired through the main gap.

Signification

Mon Aug 10 2015, 07:52AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

I have found another possibility--HV diodes for isolation, but would like comments on this or other methods. Of course the main problem is the trigger spark getting "connected" to the main discharge--even with separate grounds (isolated). I really need a way to keep the main blast isolated from the trigger through the conducting corona (of the trigger) and the plasma (of the main gap). I am unable to use an optical trigger.

Antonio wrote ...

... it's not a great problem to place the trigger electrodes in a way that avoids the main discharge touching them...

Dr. Slack

Mon Aug 10 2015, 08:44AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

If you have suitable voltages, you could use a 'gabriel' gap. Serach on this forum for some initial links.

You must set gaps to withstand the main voltage, but breakdown at half the voltage. You would need main voltage >>3kV for gap stability. If you want to fire at various voltages, then forget it, it's probably not worth the readjustment for each change.

What happens is a centre electrode gets biassed to the mean of the main electrode potentials, via a high value resistive divider. Both sub-gaps withstand the v/2. To fire, open circuit one of the divider resistors with a HV relay. The centre electrode charges to the electrode it's still connected to, the stressed gap breaks down, which then stresses the other gap and so the total gap breaks down.

It's a way of connecting a trigger gap to the main gap in a defined way. The trigger gap gets triggered by connecting it through a big (10M) resistor to the other eletrode

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