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Re: Breakdown voltage at submillimeter distances?
Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>
Below is some info from:
I do not know how accurate this info is.
Contact arcing. Conditions for voltage breakdown of a contact gap depend on
various geometric and environment factors. For a static gap, initiation of
an arc discharge can be related to the type of gas (air, nitrogen, hydrogen,
argon, helium), gas pressure, and gap length. Secondary variables that
influence this relationship are contact shape, material and surface texture,
gaseous contaminants such as water content, and the degree to which the gas
in the gap is being subjected to ionization. Discharge is initiated when
ions that may normally exist in the voltage charged gap are accelerated
sufficiently to generate more ions and have a number of "mean free path
lengths" in which to accomplish this. The minimum voltage for this kind of
breakdown is approximately 320 volts at any pressure for air, and at normal
atmospheric pressure is the gap length is approximately 0.0003 in. (0.0076
mm) For both shorter an longer gaps, the breakdown voltage is greater unless
the gap becomes exceedingly small (in the Angstrom range). For materially
shorter gaps, the voltage breakdown follows the rules for vacuum discharge
or direct molecular ionization.
Arcs will form in a voltage stress of approximately one half million volts
per centimeter when the gap is small compared to the mean free path length
of the gas molecules (or ions) in the gap. Therefore, when the gap is
sufficiently small, much lower voltages are capable of initiating breakdown.
Typical values are 100 volts for a gap length of 10,000 angstroms(0.001mm),
10 volts for 1,000 angstroms, or 1 volt for 100 amgstroms. At these
extremely small gaps, the contact damage caused by the breakdown is
accentuated by the discharge of the air capacitor formed by the very closely
spaced contacts(and the nearby parts of the circuit). This discharge takes
place as the closing contacts are about to meet. This arc is normally
invisible and not to be confused with visible arcing (frequently seen on the
contact closure), which is actually caused by contact reopening during
Robert (R. A.) Jones
A1 Accounting, Inc., Fl
407 649 6400
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
Sent: Monday, April 10, 2006 8:05 AM
Subject: Re: Breakdown voltage at submillimeter distances?
> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
> At 09:40 PM 4/9/2006, Tesla list wrote:
> >Original poster: "Mike" <mike.marcum@xxxxxxxxxxxx>
> >I thought air ionization/breakdown only happened above 315v?
> Those are actually different phenomena...
> Ionization will occur whenever the field is >30 kV/cm (approx),
> regardless of the gap and/ or voltage.
> Sparks/breakdown depends on both the field and the gap length.
> If you have a very short gap (or a very low density gas), you might
> not get sparks, but you might get a glow discharge or just plain old
> field emission. In either case, current flows across the gap, it
> just doesn't form a spark or arc.
> >----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
> >To: <tesla@xxxxxxxxxx>
> >Sent: Sunday, April 09, 2006 5:42 PM
> >Subject: Breakdown voltage at submillimeter distances?
> >>Original poster: Robert Clark <bobbygc2001@xxxxxxxxx>
> >> Actually I'm interested in the results at a few
> >>microns. I found this after a web search:
> >>"Under constant atmospheric conditions, it is found
> >>that the breakdown voltage of a uniform field gap may
> >>be expressed in the form:
> >> V = A*d + B*SQRT(d) where d is the gap spacing
> >>[i.e., in centimenters - Bob]
> >> For air under normal conditions:
> >> A = 24.4kV/cm
> >> B = 6.29kV/cm^1/2"
> >> Anyone know if this formula would apply or know a
> >>more accurate formula at the micron scale?
> >> Bob Clark