From: boris petkovic
Date: Fri, 18 Oct 2002 11:35:09 -0700 (PDT)
Subject: Re: [TSSP] Top Voltage
Hi Paul,
--- Paul wrote:
> purely on the
> basis of a fixed surface field (north & tssp). Are
> we seeing
> a long range effect that holds off breakout despite
> the surface
> field reaching 30kV/cm.
---
I'm not sure what phyisical processes can stop corona
development in its' inital phase near surface of small
electrodes when surface field reaches over 30
kV/cm,but might be associated with "acceleration" of
surrounding particles and some space needed to form
discharging corona structures in a small distance in
greatly variated gradients.Maybe some kind of equation
for stabilty like for soap bubbles?Well,here are other
things in a game such as various mobilities of charge
carriers,dynamic changing of microlocated surface
fields due to displacement polarisation effects etc.
Just guessing.
I don't trust 30 kV/cm for OLTC rod/sphere setup.
Yes,there is always increased error in software max
field evaluation if the object is like that one,but I
feel error isn't as gross as x2!
(In other words you're not an idiot)
Equations of Ps.' types where geometry is defined
,voltage given and picture of E field unknown can be
sometimes problematic.
--->
field gradient just above the electrodes,
> effectively increasing
> the ROC a little, and allowing some further voltage
> rise before
> discharge. Is that what we're seeing with this
> difference
> between north and AIEE?
---
Haven't read any of that two.Hence, wouldn't know.
---
>
> Extrapolating to the case of the small sphere on
> OLTC, this
> could easily account for considerably higher
> breakout voltage
> measured.
---
Concentrate just on max E field issue.
---
>
> Is this the space charge effect that others have
> mentioned? If
> so we seem to be acquiring some sort of numerical
> handle on it.
---
Do you refer to space charge debris from previous
shots or consider just one shot (without coil
operating hystory)?If second,than you must be thinking
of excited charge in quasyneutral gas without or with
just a small conduction current from electrode in
space.If small conductive current flows continuiosly
from rod/sphere in gap (that's not what Terry
recorded) and in same time there is induction current
in the electrode due to space charge displacement
current ,than, it would be very tricky to distinguish
what is what.
But in principle ,these two currents cannot cancel in
our case and msm of current tru rod can give some
insights.First ,one measures that current in case of
low energy (low voltage) ,than increases precisely
that energy and measure current again.If nothing
happens "above" 2 currents should be exactly
proportional with the increase of the voltage.
Clearly speaking,we are looking for some variation in
capacity of rod/sphere system.
Note that if some charge being periodicaly pushed in
gap and returned ,capacitor connected to the bottom of
resontor needn't show that.
However,I don't expect that to happen if Terry reports
he sees nothing in dark around electrode during the
shots.But again ,eyes are inperfect registration
devices..
---
Perhaps we can make an
> initial
> guess of how much space charge is formed per unit
> volume for
> a given background E-field uniform in that volume?
--
If we are looking for the threshold of just one shot
without previous coil influences in a long gap like
the one of present OLTC's ,than total amount of charge
=0 since drift times are too long for the
mode.However,there could be LOCAL charge produced.The
question is :does always that charge increases E-field
near electrode or some other pecularities considering
TC wave are possible,in order to not increase but to
decrease the field?
Hard speculations.But we are desperate without
experimental evidence.
---
> Of course, it would be nice to have some evidence
> that space charge
> is holding off breakout. It would have to show up
> as an increase
> in the apparent C of the terminal.
---
(see above)
---
And maybe it
> would also leave
> behind a negative static charge on the terminal, as
> we've seen.
---
Well TCs are known to do such things.There was beleif
that it is becouse of their inperfect sine wave ,but
that is not a complete truth.AC sine wave coronas also
have some rectification effects and give away charge
in gap.
---
>
> So if any of this is realistic..
---
Many things are not realistic,but the effects are more
easily explained taking them for granted,as they were
present.All this reminds me of electron charge
definition problems in physics:"Bare" or "naked"
electron charge and observed electron charge which is
smaller ( vacuum polarisation and presence of virtual
particles charges shielding it ).
---
>
> Does this approach consolidate everyone's thoughts
> on the subject?
> --
The "subject" drives me crazy.More and more
questions,a very few answers.
Cheers,
boris
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