Yahoo Answers: Answers and Comments for HOW DOES VOLTAGE VARY WITH ALTITUDE AND TEMPERATURE? [Aircraft]
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From angus c
enUS
Mon, 19 Dec 2005 15:13:03 +0000
3
Yahoo Answers: Answers and Comments for HOW DOES VOLTAGE VARY WITH ALTITUDE AND TEMPERATURE? [Aircraft]
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From Anonymous: you didnt specify whether you meant high or lo...
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https://answers.yahoo.com/question/index?qid=1005121902870
Tue, 20 Dec 2005 01:30:13 +0000
you didnt specify whether you meant high or low voltage. additionally you didnt specify ac or dc. but....
In 1889, F. Pashchen published a paper which set out what has become known as Paschen's Law. The law essentially states that the breakdown characteristics of a gap are a function (generally not linear) of the product of the gas pressure and the gap length, usually written as V= f( pd ), where p is the pressure and d is the gap distance. In actuality, the pressure should be replaced by the gas density.
For air, and gaps on the order of a millimeter, the breakdown is roughly a linear function of the gap length: V = 30pd + 1.35 kV, where d is in centimeters, and p is in atmospheres.
Much research has been done since then to provide a theoretical basis for the law and to develop a greater understanding of the mechanisms of breakdown. It should be realized that there are many, many factors which have an effect on the breakdown of a gap, such as radiation, dust, surface irregularities. Excessive theoretical analysis might help understanding why a gap breaks down, but won't necessarily provide a more accurate value for the breakdown voltage in any given situation.
Paschen's Law reflects the Townsend breakdown mechanism in gases, that is, a cascading of secondary electrons emitted by collisions in the gap. The significant parameter is pd, the product of the gap distance and the pressure. Typically, the Townsend mechanism (and by extension Paschen's law) apply at pd products less than 1000 torr cm, or gaps around a centimeter at one atmosphere. Furthermore, some modifications are necessary for highly electronegative gases because they recombine the secondary electrons very quickly.
In general, an equation for breakdown is derived, and suitable parameters chosen by fitting to empirical data.
Here are three equations:
Breakdown voltage:
Vbreakdown = B * p * d / (C + ln( p * d))
Breakdown field strength:
Ebreakdown = p * ( B / ( C + ln ( p * d)))
where:
C =ln( A / ln ( 1 + 1 / gamma))
where:
gamma is the (poorly known) secondary ionization coefficient.
For air:
A = 15 cm1Torr 1
B = 365 Vcm1 Torr1
and gamma = 102
so
C = 1.18
Minimum sparking potential for various gases
Gas Vs min
(V) pd at Vs min
(torr cm)
Air 327 0.567
Ar 137 0.9
H2 273 1.15
He 156 4.0
CO2 420 0.51
N2 251 0.67
N2O 418 0.5
O2 450 0.7
SO2 457 0.33
H2S 414 0.6
Note that the sparking voltage is affected by the electrode material, with cathodes of Barium and Magnesium having higher voltages than Aluminum, for example.
Temperature dependence
Paschen's law ( V = f(pd)) should really be stated as V = f( Nd) where N is the density of gas molecules, which is, of course, affected by the temperature as well as the pressure of the gas ( n/V = p/RT). An empirical formula for air (considering it as an ideal gas) is:
x = 293 * p * d / (760 * T)
Vbreakdown = 24.22 * x + 6.08 * SQRT(x)
p = pressure in Torr (mm Hg),
d = distance in cm,
T = Temperature in Kelvins
Vbreakdown in kV
Humidity dependence
In air, increasing humidity increases the breakdown voltage. The effect is most noticeable in uniform field, and less important in nonuniform gaps (such as sphere gaps where the gap is a large fraction of the sphere diameter, or in rod or needle gaps). An emprical expression for this is:
(not here yet)
Gamma  Townsend's secondary ionization coefficient
Gamma is the net (!) number of secondary electrons produced per incident positive ion, photon, excited or metastable particle. It is a function of gas pressure and E/p. Electronegative gases (SF6, Freon, oxygen, CO2) reattach the electrons very quickly, so they have low gammas.
For nitrogen, gamma ranges between 103 and 102 for E/p of 100700 V cm1 torr1. Insulating gases like SF6 or Freon have gammas of 104 or even less.

From halbert: ninety 8.6 is merely the final for most folk. ...
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https://answers.yahoo.com/question/index?qid=1005121902870
Tue, 13 Dec 2016 10:12:32 +0000
ninety 8.6 is merely the final for most folk. couple of tiers larger or decrease is okay in case you many times have that temperature. i'd nevertheless attempt measuring your temperature from yet another spot on your body. Your mouth isn't the most precise. if you're incredibly anxious a common practitioner ought to verify you with a rectal thermometer. reliable success

From RUNINTLKT: Yep, What he just said
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https://answers.yahoo.com/question/index?qid=1005121902870
Fri, 23 Dec 2005 06:18:12 +0000
Yep, What he just said