I Dielectric breakdown voltage of air vs. Electric field in thunderstorm

[ilovepudding]

The dielectric strength of air (ie the maximum electric field that the material can withstand under ideal conditions without undergoing electrical breakdown and becoming electrically conductive) is 3 000 kV ( https://en.wikipedia.org/wiki/Dielectric_strength#Break_down_field_strength ).

In many articles I have read, some facilities that need lightning protection like NASA's Kennedy Space Center, electric field mills are used to measure the electric field's magnitude. When it reaches a certain threshold, there is a risk of lightning occurrence and so, all operations are suspended.

This threshold is usually situated between 1kV and 3kV ( https://www.vaisala.com/sites/defau...ric_field_mill_and_lightning_observations.pdf p : 4 ), and I find this really curious since air can't conduct electricity unless the electric field is 3000kV in normal conditions, which is not even close to the threshold chosen.

Is there any explanation for this apparent contradiction?
Thanks.

 

[berkeman]

Electric field strength has units of V/m (or kV/m or MV/m), not Volts.

The 3MV/m number from Wikipedia is for dry air, so I'm guessing that you would set the threshold much lower under real conditions (high humidity, rain, etc.).

 

[tech99]

It also depends on the sharpness of the points on the structure. Sharp points create a stronger field. Lightning is unpredictable, and will sometimes strike low down on a tall structure, for instance. Conditions are likely to vary from minute to minute, so a lower threshold will give more warning.

 

[berkeman]

@ilovepudding -- this thead is locked temporarily until you respond to my PM

 

[berkeman]

@ilovepudding -- this thead is locked temporarily until you respond to my PM

There has been no reply to my PM, but the issue was handled another way. Thread is re-opened.