Dielectric strength of air

[PJ]

How is the dielectric strength of air affected in reality. Consider dust, humidity, temperature, and air pressure, how much lower or higher does the 3 kV/mm value go?

[SH3RL0CK]

IMO, there are too many variables to provide an accurate answer within this forum. In addition to the dust, humidity, temperature, air pressure variables you have identified, there are many others. Electrode size, shape, orientation, finish and material have effects. Frequency of the electrical system of concern has an effect. The distance between electrodes has a very great effect when converting the voltage breakdown and distance into a kV/mm number. For most materials (I believe including air), the smaller the distance between the electrode, the higher the kV/mm number becomes. Want a higher kV/mm value? Simply reduce the thickness of the material being tested until you get this value.

 

How much can all this vary? Depends on what constraints on the above is realistic for your application. Is a 1 kilometer air gap realistic to you? It is if you are discussing lightning. Is a 1 um air gap realistic? It may be if you are discussing electronics.

 

These issues are understood and the math for them is known. However, this gets very complicated, well beyond my capabilites to explain in a forum here, unfortunately.

[PJ]

Thanks Sh3lock - I figured I'll need to give more information but in essence, the question arises from a potential discharge between a plastic board and a metal grid, The distance is about 30 mm. When creating a static charge, I can measure 15kV with this device http://www.detectortechnologies.com/store/detail.aspx?ID=20. Considering the 3kV/mm I shouldn't see or hear arcing over that distance ... I could probably come up witha little higher voltage but for 30 mm that would require almost 100kV ... So I feel like I am missing something.