Date: Wed, 10 Mar 2010 00:12:37 +0000 (GMT)
From: "Alexander S. Yurkov" <fitec@omskcity.com>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <4B9678C3.7070907@iup.uni-heidelberg.de>
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Subject: Re: LF: Possible VLF HV problems, or not?
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On Tue, 9 Mar 2010, [ISO-8859-1] Stefan Sch=E4fer wrote:
>=20
> I have had some thoughts about HV problems when operating a vertical=20
> 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:-)

>=20
> Normally, e.g. in a 50Hz system there will flow a current into the air=
=20
> (capacitive with a restistive component) due to the ionisation of the=20
> air when partial discharges occur.
> This is due to exceeding the maximum E field strange on the wire (a=20
> function of its radius and geometry and insulation and the gap between=
=20
> wire and insulation and the epsilon r of the insulation and and and ...=
=20
> ;-) ).
> In the special case of a VLF antenna there might be some special=20
> conditions that can limit the influence of the partial discharges. For=
=20
> example, the Z  (sqrt (L/C) of such an antenna is very high, so the=20
> resonance is quickly lost if C is changing slightly. The presence of=20
> partial discharges will apparently increase the C since the surface is=
=20
> virtually increasing. There will be additional resistive losses but=20
> since a change the C will bring the circuit out of resonance (what would=
=20
> reduce the voltage at the wire), there might be a limitation of the=20
> momentary value of the voltage. This will be anything else than a stable=
=20
> process but there might be the effect, that the voltage will be limited=
=20
> like with a varistor or a spark gap in series with a resistor. So,=20
> theoretically, there will be many harmonics and my signal might be=20
> better visible at its harmonics than on the ground wave ;-) So, have=20
> some of you, perhaps on LF, have experiences with theese effects??
>=20
> 73, Stefan/DK7FC
>=20


Regards,
Alexander