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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
[quote] If I set a safety spark gap to fire at x volts, how much variability of firing voltage should I expect for different air moistures, temperatures etc.?
[/quote]
Increasing humidity will increase the breakdown voltage necessary to arc.
Temperature really isn't a good parameter for variability. Its more correct to say variability in terms of density of air which is affected both by pressure and temperature.
Google Paschen's Curve. This will give you some background into what you seek.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Dr. Kilovolt wrote ...
But the humidity isn't implemented in the Paschen's law...
E. Kuffel has done extensive studies on the effect of humidity and breakdown voltage. A search on IEEE archives should bring up some of his research and studies.
Humidity is a bit more complex and the effect is has on breakdown voltage varies substantially as the electrode geometry changes. (i.e. different sized spheres, etc...)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Hi Kilovolt
The "Paschen breakdown voltage" - by which I mean the voltage at which the insulation of air breaks down leading to a Townsend avalanche allowing ions to flow across the gap - is probably good enough for general purposes, but does not take into account the pre-discharge state, especially variations of leader growth due to impulse rise time and the geometry of the gap,
To the best of my knowledge, the length of the coronal phase of dielectric breakdown in a gas varies with the impulse voltage wavefront, which happens because of the space charge caused by electric field distortion - the space charge itself being produced by the initial corona. The effect of this space charge is to create a statistical time delay in the breakdown of the gap. In a word, it is impossible to calculate the precise time at which a gap will break down, but only to talk of it in terms of probability, and greatest likelyhood.
Even the source impedance of your high voltage supply can influence the breakdown behaviour of your gap, so while we get the impression of a spark as a single snap and a flash of light, what we are seeing is not a single event at all, but a complex sequence of intertwined events each one of which is subject to what I'll call mini-variables.
As for safety gaps, I'm all for an easy life, and would just take one out of the box and solder it in.
Registered Member #1889
Joined: Mon Dec 29 2008, 07:36AM
Location:
Posts: 55
Harry wrote ...
Hi Kilovolt
The "Paschen breakdown voltage" - by which I mean the voltage at which the insulation of air breaks down leading to a Townsend avalanche allowing ions to flow across the gap - is probably good enough for general purposes, but does not take into account the pre-discharge state, especially variations of leader growth due to impulse rise time and the geometry of the gap,
To the best of my knowledge, the length of the coronal phase of dielectric breakdown in a gas varies with the impulse voltage wavefront, which happens because of the space charge caused by electric field distortion - the space charge itself being produced by the initial corona. The effect of this space charge is to create a statistical time delay in the breakdown of the gap. In a word, it is impossible to calculate the precise time at which a gap will break down, but only to talk of it in terms of probability, and greatest likelyhood.
Even the source impedance of your high voltage supply can influence the breakdown behaviour of your gap, so while we get the impression of a spark as a single snap and a flash of light, what we are seeing is not a single event at all, but a complex sequence of intertwined events each one of which is subject to what I'll call mini-variables.
As for safety gaps, I'm all for an easy life, and would just take one out of the box and solder it in.
And as for "extremely straight forward".....get owned
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Air breakdown voltage variability
