MMC corona

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi All,

While working on an experimental MMC, I hooked the Bertran directly across
two strings and charged the string ends to 24kV.  With my Olympus 3000
digital camera I was able to take a pretty good picture of the corona
between the strings:

http://hot-streamer-dot-com/TeslaCoils/Misc/MMCglow.jpg

This discharge starts at around 17kV and just gets worse as the voltage is
raised until it arcs over at about 25kV.  The terminals are 1.5 inches
apart center to center.

With a 15kV NST, the voltage between a dead and live string (this MMC is
specifically made to have selectable strings) would be only 11kV peak AC.
So It is probably ok but I thought I would share this info.  

Since it is really hard to solder up an MMC with ball solder joints to
resist corona, there is probably a voltage level (~30kV) where streamers
will start to propagate or arcing will make an MMC impractical.  Thus if
one were to try and make an MMC for say a 50kV transformer, it would need
to be submersed in oil or something to stop this corona and the inevitable
destruction it would do at very high voltages regardless of the number of
caps per string.

I should also mention that this was done at DC and the charging of the
lexan and me was significant.  I could get steady 1/8 inch arcs about once
a second from my finger to a grounded object.  Some serious fields are
present!  Also the negative side started corona much earlier than the
positive as expected.

A person had a problem with terminal to terminal arcing and this experiment
does not show any unusual problem.  However, perhaps my 1.5 inch spacing is
greater than in his case?

Cheers,

	Terry