Relative Dielectric Strengths of Gases: (0.1 in ga')
Air: 0.95,
N2: 1.0,
CO2: 0.90,
H2: 0.57,
A: 0.28,
Ne: 0.13,
He: 0.14,
SF6: 2.3 - 2.5,
C1F4: 1.1,
C2F6: 1.9,
C3F8: 2.3,
C4F8: 2.8,
CF2CL2: 2.4,
C2F5CL: 2.6,
C2F4CL2: 3.3
Sphere-gap Spark-over Crest Voltages:
(from AIEE Standard No. 4)
At 25° C and 760 mm Barometric Pressure; one sphere grounded.
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Sphere Diameter = 6.25 cm:
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Sphere Gap Spacing, in cm: 0.5 cm
60 Hz, Negative Impulse KV Crest: 17.0 KV
Positive Impulse KV Crest: 17.0 KV,
Sphere Gap Spacing, in cm: 1.0 cm
60 Hz, Negative Impulse KV Crest: 31.3 KV
Positive Impulse KV Crest: 31.3 KV,
Sphere Gap Spacing, in cm: 1.5 cm
60 Hz, Negative Impulse KV Crest: 44.5 KV
Positive Impulse KV Crest: 44.8 KV,
Sphere Gap Spacing, in cm: 2.0 cm
60 Hz, Negative Impulse KV Crest: 57.0 KV
Positive Impulse KV Crest: 57.4 KV,
Sphere Gap Spacing, in cm: 2.5 cm
60 Hz, Negative Impulse KV Crest: 68.8 KV
Positive Impulse KV Crest: 69.3 KV.
I am sure this is not what you are looking for, but it may be of some assistance.
Scott35
btw, I seem to remember a figure of 100 KV / Meter in moist air ( >85% Humidity, < 29.00 mbar ), for the dielectric breakdown point of a "Typical" mole of air. This was in reference to Lightning.
LarryC's reference to 10 KV / Inch for Dry, "Clean" Air sounds familiar also.
Scott 35
