From: Bert Hickman
Date: Tue, 29 Oct 2002 10:39:39 -0600
Subject: Re: [TSSP] Top Voltage
Ralph and all,
The initial formation of corona at the surface of an electrode in a
highly nonuniform field occurs at a surface E-field of ~25-30 kv/cm.
This is a very low current discharge (microamperes). Initial corona
breakout preferentially occurs when the electrode has a negative
polarity. Formation of streamers ("cold" filamentary discharges that
extend a significant distance from the electrode) will not occur until
the electrode is driven to a significantly higher potential. These are
very brief (10-50 nS), higher current discharges (peaks reaching ampere
level). The hot discharges that Tesla Coilers are interested in are
leaders, and these hotter conductive plasma channels behave more like an
arc and typically carry peak currents of amperes to perhaps tens of
amperes. Leaders are "fed" by all the combined streamer currents
converging at the the tip of the leader. Leader and streamer propagation
require a rising d|v|/dt.
Unlike initial corona breakout, "long" sparks (for DC, Low Frequency AC,
and unipolar impulses) seem to propagate more efficiently (at a lower
electrode voltage) when the active electrode is positively polarized and
streamers and leaders are "cathode-directed". However, it's not
presently known if the presence of space charges (from previous partial
discharges) significantly alters the positive polarity preference in
"long", low frequency RF air discharges. There's simply not very much
about long RF discharges in the literature, and interpreting the few
existing measurements taken via the OLTC is subject to somewhat
conflicting interpretations - there are simply too many variables at
present. This is going to be a tougher nut to crack...
Best regards,
-- Bert --
--
Bert Hickman
Stoneridge Engineering
"Electromagically" (TM) Shrunken Coins!
http://www.teslamania.com
Parpp807@aol.com wrote:
> In a message dated 10/27/02 11:44:39 PM Central Standard Time,
> bert.hickman@aquila.net writes:
>
>
>>However, complex interactions between
>> increasingly higher terminal voltage oscillations and space charges left
>> over from previous polarity excursions makes analysis extremely
>> challenging...
>
>
> Bert and Boris,
>
> Probably a very naive Q:
>
> What are the conditions prevailing at the original BO when there is no
> residual
> space charge? Can we predict whether the first streamers will be anode
> directed
> or cathode directed as the polarity changes?
>
> Hope I phrased that with sufficient clarity.
>
> Regards,
> Ralph Zekelman
>
>
>
>
>
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.