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Old 10-20-2005, 08:42 AM
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RickI RickI is offline
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Any RF, electrical engineers/technicians, physicists, informed individuals, etc. with insight on these and other influences (including atmospherics) on static electric discharges from kite lines? Also of interest are semiconductor properties of Dyneema/Spectra (HDPE) line/related effects and altered conducting properties induced by saline moisture and charged atmospheric aerosols.

It seemed like a simple question, "what causes electrostatic kite line discharges?" The potential answer(s) seem to be growing more complex rapidly.

Thanks!


More on the technical side of static discharges from kite gear appears at:
http://www.kiteforum.com/phpbb/viewtopic.php?t=2318240


Wow, thanks for all the input. In my experience these electrostatic kiting discharges have been mildly to fairly painful, noisy on occassion and by one telling, even visible as an arch that followed a jumper. I have some concerns that some sources of electrostatic discharge include some that may closely preceed lightning.

Some of the things that have come up so far in trying to explain causes for electrostatic kite line discharges follow.

Voltage gradient -

Manfred summed it up well as:

"1.: in weather near to a lightning, even if there actually is no lightning,
there can occure potentials of more than 10.000V/m (vs sunshine 100-300v/m). If you jump up then, you (your kite and yourself) can easily load up to 150.000V - when you touch ground there may be a small lighning. "

This has been an issue with balloons with conductive tethers, kite lifting antennas and has resulted in a lot of damaged equipment. Regarding injuries?


Dyneema and Spectra are made of HDPE, a poor conductor or semiconductor in dry conditions. Still, if I have it right, these materials can develop significant charges through the Electret Effect.

****ney Lad provided input in this direction with:

"Dry kite line might be an insulator but it can still be used to generate / hold a charge. Pulling an insulator through a charged environment such as dry kite lines in a charged airflow sounds a lot like a van de graff generator to me.

ZAP! don't do it...."

I understand that this is the case with Cable Generators that utilize the Electret effect that are similar to Van De Graff generators.


Chis Glazier indicated:

"First of all understand that spectra or dyneema kitelines are excellent insulators and do not conduct electricity. Otherwise every power line incident involving a kiteboarder would certainly result in a dead kiteboarder. However if kite lines are wet with salt water, they may may not be good insulators. Interestingly, fresh water is quite a good insulator and does not conduct electricty very well. "

The poor conductor part is true but then there may be the Electret effect at work as well. In the past the coating of the exterior of the line with saline water was the only way I could explain electrostatic discharges. I didn't think about the possible contribution of aerosols discussed below.


Aerosols can also contribute to charge development:

"Still another source of atmospheric charge collected by the cable generator are Aerosol Charges. These are particles of dust or water which form dipoles and disproportionately collect one charge or the other. Where ions carry only single or double units of charge, Aerosols carry 100's to 10's of thousands of units of charge. The fact humidity is such an important factor in the output of the cable generator indicates that aerosols are an important source of the energy it collects.."
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Last edited by RickI; 09-10-2008 at 10:21 PM.
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