Re: Break-down voltage of gaps and humidity

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net> 


Tesla list wrote:

>Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>
>
>Regarding humidity and the effect of it on break-down voltage:
>In testing, I (as well as others) may have noticed that corona discharge
>increases from a high voltage point in the
>presence of increasing humidity.
>However, in Kuffel's High Voltage Engineering text, he states that the
>break-down voltage between two gaps will
>actually increase with increasing humidity.
>This seems to contradict what I have experienced.  Can anyone comment on
>this?
>Thanks
>Dan

Hi Dan,

Humidity has a greater impact on long spark/streamer development than for 
short gaps. Increasing the water vapor content has the effect of increasing 
the terminal voltage that's necessary to make the transition from a corona 
discharge to a propagating streamer.

  A number of coilers have noticed that if their systems are designed so 
that the toroid barely "breaks out", these systems may have great 
difficulty breaking out on a humid day, and that the resulting streamers 
will tend to be shorter than on colder/dryer days. Water vapor is an 
electronegative gas - it readily absorbs free electrons, reducing the 
number of free electron necessary to form the avalanches that are essential 
for streamer inception and growth. Water vapor also absorbs ultraviolet 
light, reducing the creation of secondary electrons from photoionization if 
we are successful in generating a streamer.

BTW, an excellent book recently became available for those folks who are 
seriously interested in better understanding long spark formation and 
propagation:
"The Lighting Flash" by Vernon Cooray, IEE, ISBN 0852967802, 2003, 574pp.

Best regards,

-- Bert --
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