Re: Break-down voltage of gaps and humidity

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

Original poster: dhmccauley-at-spacecatlighting-dot-com 

What is really weird is that in very humid conditions, it seems corona forms
more readily.  There are two instances that come into mind:

1.  When doing hi-pot or corona testing on high voltage cabinets (i.e. big
radar transmitters, hv linear supplies, etc....), there are always more
corona hisses
and spits during those most humid days than on drier days.

2.  When bicycling up in the mountains, it is always on those most hot and
humid of nights that the power lines on big HV transmission lines spit and
hiss more.

Anyone have an idea of why this is?

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 --
 > --
 > -
 >
 >
 >
 >
 >