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Date: Tue, 9 Mar 2010 20:14:45 +0100
Message-ID: <38A51B74B884D74083D7950AD0DD85E82A1B46@File-Server-HST.hst.e-technik.tu-darmstadt.de>
Thread-Topic: LF: Possible VLF HV problems, or not?
Thread-Index: Acq/sW75YsY4YLePQiC1xi+ZqbMtWwACJN5i
References: <9afca2641003090337t4062bb3avc9b952612014c0ba@mail.gmail.com> <4B9678C3.7070907@iup.uni-heidelberg.de> <4B9689B9.8030805@abelian.org>
From: =?iso-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@hst.tu-darmstadt.de>
To: <rsgb_lf_group@blacksheep.org>
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Subject: AW: LF: Possible VLF HV problems, or not?
Sender: owner-rsgb_lf_group@blacksheep.org
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Reply-To: rsgb_lf_group@blacksheep.org


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I'll just ignore the problems that will occur, so easy is the game. There=
 will be partial discharges at 10kV rms and not only at the end. Who tells=
 that they are just to find at the end? Sure, there the field is maximum=
 inhomogenious but the difference to the center of the wire (50m hight) is=
 not to much.
=20
In the power grid, say in the 20kV (up to 123kV) field you do not really=
 have problems with PD at the normal wires but there we are talking about=
 a wire radius of abt 2cm. My antenna has a wire of 1mm diameter! That is=
 a complete different case since E falls and rises with 1/r.
But anyway, slight PDs are no problem. And the power grids does also produ=
ce PDs all the time. Just drive with your car under a 400kV line and liste=
n to the AM MF band and you know what i mean ;-)=20
=20
Just let's see what we get in the next test...=20
=20
73, Stefan/DK7FC
=20
=20
=20

________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Alexander S. Yurkov
Gesendet: Mi 10.03.2010 01:12
An: rsgb_lf_group@blacksheep.org
Betreff: Re: LF: Possible VLF HV problems, or not?



On Tue, 9 Mar 2010, [ISO-8859-1] Stefan Sch?fer wrote:
>
> I have had some thoughts about HV problems when operating a vertical
> antenna wire at some 10kV.

Dear Stefan,
there was no such a problem (seems to me) in Markus experiment with 10kV.
May by with 20kV... But anyway corona protected rings (rather small i
think) to be usefull on the ends of wire. Remember, high E is only arround
ends of wire, not at the center of wire. Besides such a problems arises in
50 Hz systems at some about 100kV, not at 10 kV. 10 kV is rather small
voltage:-)

>
> Normally, e.g. in a 50Hz system there will flow a current into the air
> (capacitive with a restistive component) due to the ionisation of the
> air when partial discharges occur.
> This is due to exceeding the maximum E field strange on the wire (a
> function of its radius and geometry and insulation and the gap between
> wire and insulation and the epsilon r of the insulation and and and ...
> ;-) ).
> In the special case of a VLF antenna there might be some special
> conditions that can limit the influence of the partial discharges. For
> example, the Z  (sqrt (L/C) of such an antenna is very high, so the
> resonance is quickly lost if C is changing slightly. The presence of
> partial discharges will apparently increase the C since the surface is
> virtually increasing. There will be additional resistive losses but
> since a change the C will bring the circuit out of resonance (what would
> reduce the voltage at the wire), there might be a limitation of the
> momentary value of the voltage. This will be anything else than a stable
> process but there might be the effect, that the voltage will be limited
> like with a varistor or a spark gap in series with a resistor. So,
> theoretically, there will be many harmonics and my signal might be
> better visible at its harmonics than on the ground wave ;-) So, have
> some of you, perhaps on LF, have experiences with theese effects??
>
> 73, Stefan/DK7FC
>


Regards,
Alexander





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