From: Paul
Date: Tue, 07 May 2002 08:37:36 +0100
Subject: Re: [TSSP] Secondary voltage stress factor
This is a multi-part message in MIME format.
--------------8070DD279992D7CE9A3EE753
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Forwarded from Malcolm:
--
Paul Nicholson,
--
--------------8070DD279992D7CE9A3EE753
Content-Type: message/rfc822
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Return-Path:
Received: from finch-punt-12.mail.demon.net (finch-punt-12.mail.demon.net [194.217.242.36])
by abelian.demon.co.uk (8.11.2/8.11.2) with SMTP id g4667rs08506
for ; Mon, 6 May 2002 07:07:54 +0100
Received: from punt-1.mail.demon.net by mailstore for paul@abelian.demon.co.uk
id 1020650035:10:02048:0; Mon, 06 May 2002 01:53:55 GMT
Received: from its-mail1.massey.ac.nz ([130.123.128.11])
by punt-1.mail.demon.net id ab1001450; 6 May 2002 1:53 GMT
Received: from its-mm1.massey.ac.nz (its-mm1.massey.ac.nz [130.123.128.45])
by its-mail1.massey.ac.nz (8.9.3/8.9.3) with ESMTP id NAA22076
for ; Mon, 6 May 2002 13:53:12 +1200 (NZST)
Received: from its-campus1.massey.ac.nz (not verified[130.123.32.254]) by its-mm1.massey.ac.nz with MailMarshal (4,2,5,0)
id ; Mon, 06 May 2002 13:53:11 +1200
Received: from it015563 (it015563.massey.ac.nz [130.123.161.49])
by its-campus1.massey.ac.nz (8.9.3/8.9.3) with ESMTP id NAA26141
for ; Mon, 6 May 2002 13:53:07 +1200 (NZST)
From: "Malcolm Watts"
To: Paul
Date: Mon, 6 May 2002 13:53:06 +1200
MIME-Version: 1.0
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Subject: Re: [TSSP] Secondary voltage stress factor
Reply-to: M.J.Watts@massey.ac.nz
Message-ID: <3CD68AC2.6631.12D56DB@localhost>
Priority: normal
In-reply-to: <3CD5AB19.4F27158C@abelian.demon.co.uk>
X-mailer: Pegasus Mail for Win32 (v3.12c)
X-Mozilla-Status2: 00000000
Hello all,
On 5 May 2002, at 22:58, Paul wrote:
> Boris wrote:
>
> > In this way dielectric objects (insulators here) act like
> > sort of lens and the effect of coverging E-field lines is most
> > expressed in surface of the dielectric while voltage
> > between big plate electrodes remained same as before.
>
> > I hope I made my point clearer now.
>
> Yes, I do see what you mean. With a perfect smooth coating
> this probably wouldn't be an issue, but as you say, local
> non-uniformities in the dielectric coating, eg a bubble, or
> something stuck to the surface, would give non-uniformity to
> the E-field in that region, thereby creating points where
> the local field exceeds the average.
>
> So we should think in terms of two sources of non-uniformity,
>
> a) that due to the voltage profile, giving rise to the stress
> factor under discussion;
> b an additional non-uniformity due to surface irregularity,
> giving rise to an additional factor increase in the peak
> field strength.
>
> Perhaps we should have a stress factor and a surface quality
> factor, the product of the two multiplying the average gradient
> to give a working value for the peak gradient.
>
> We really do need some hard data on this. If we new at what
> primary voltage particular coils developed racing arcs, then
> we could calculate the voltage gradient due to (a), and if
> this falls short of 26kV/cm, we could lump the remaining
> coefficient into a 'surface' factor. Of course, we'd need
> to look at quite a few coils to see if there was any
> consistency to such a surface quality factor.
>
> Q to all: Do racing arcs tend to occur before topload breakout,
> as the power is turned up, or do they appear at the same time?
> I think I may have asked this before, perhaps someone could
> remind me?
Perhaps we should exclude detuned coils from the considerations as
all sorts of anomalous behaviour can arise is such a case. I've seen
racing arcs both with and without breakout depending on the
particular setup. For example, putting a topload with too large a ROC
on top for the output voltage produced and cranking up primary energy
can easily induce unwanted discharges.
> The traditional cure seems to be to reduce coupling, so K must
> be a factor, but it doesn't look very promising from the
> data in pn040502. I'll redo some of those tomorrow, normalising
> the primary energy instead of the primary voltage. I think
> I'll also plot a set of those gradient animations, ie showing
> the |dV/dx| rather than V.
Reducing the size of topload can reduce if not eliminate the problem
but as always, in changing the Ctop, something about the primary is
also changed to maintain tune.
> And concerning strikes that hit the secondary, do these occur
> only when the top is breaking out?
Is that from primary to secondary?
Regards,
malcolm
--------------8070DD279992D7CE9A3EE753--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.